Pre-Endcapping of Hyperbranched Polymers toward Intrinsically Stretchable Semiconductors with Good Ductility and Carrier Mobility

The advancement of semiconducting polymers stands as a pivotal milestone in the quest to realize wearable electronics. Nonetheless, endowing semiconductor polymers with stretchability without compromising their carrier mobility remains a formidable challenge. This study proposes a "pre-endcapping" strategy for synthesizing hyperbranched semiconducting polymers (HBSPs), aiming to achieve the balance between carrier mobility and stretchability for organic electronics. The findings unveil that the aggregates formed by the endcapped hyperbranched network structure not only ensure efficient charge transport but also demonstrate superior tensile resistance. In comparison to linear conjugated polymers, HBSPs exhibit substantially larger crack onset strains and notably diminished tensile moduli. It is evident that the HBSPs surpass their linear counterparts in terms of both their semiconducting and mechanical properties. Among HBSPs, HBSP-72h-2.5 stands out as the preeminent candidate within the field of inherently stretchable semiconducting polymers, maintaining 93% of its initial mobility even when subjected to 100% strain (1.41 ± 0.206 cm2 V-1 s-1). Furthermore, thin film devices of HBSP-72h-2.5 remain stable after undergoing repeated stretching and releasing cycles. Notably, the mobilities are independent of the stretching directions, showing isotropic charge transport behavior. The preliminary study makes this "pre-endcapping" strategy a potential candidate for the future design of organic materials for flexible electronic devices.

Novel Beta-Functionalized Porphyrins Approaching 11% Efficiency for Organic Solar Cells

Porphyrins and their derivatives possess high molar extinction coefficients and strong electron-donating abilities and have been widely used in organic solar cells (OSCs). Though porphyrins can be easily functionalized at the four meso-positions and the eight β-positions, nearly all porphyrin photovoltaic materials are reported to be functionalized at the meso-positions, and the porphyrin photovoltaic materials functionalized at the β-positions are to be explored. Herein, the regioselective β-positions of a porphyrin are first brominated without using rare metal iridium catalysts, and then, after two more reactions, two antipodal β-substituted porphyrin donors EHDPP-Por and BODPP-Por are synthesized, in which four DPP (diketopyrrolopyrrole) units are connected symmetrically with acetylene at four of the β-positions, for OSCs. The all-small-molecule organic solar cells based on EHDPP-Por:Y6 and BODPP-Por:Y6 active layers achieved power conversion efficiencies of 10.19 and 10.99%, respectively, which are higher than most of the binary OSCs based on the porphyrins functionalized at the meso-positions, demonstrating that β-functionalized porphyrins are very promising for OSCs.

Photophysics of Benzoxazole and Dicyano Functionalised Diketopyrrolopyrrole Derivatives: Insights into Ultrafast Processes and the Triplet State

Diketopyrrolopyrrole (DPP) functionalised with an electron donating unit acts as a donor-acceptor molecules that have shown potential for application in dyes and photovoltaics. These molecules offer broad absorption/emission properties and structure-dependent dynamics. In this study, we used femtosecond pump-probe spectroscopy to investigate the photo-initiated dynamics of thiophene linked DPP derivatives. The thio-DPPs are further functionalised by different electrons withdrawing terminal groups, namely benzoxazole and thiophene dicyanide. The benzoxazole derivative is strongly emissive and directly relaxes directly to the ground state chloroform solution. Thiophene dicyanide derivative exhibits distinct spectral evolution in the first 10 ps, associated with structural and vibronic process. Later, it crosses over to the triplet state with a yield of 20 %. In the solid-state (thin film), we observed a signal that resembles singlet fission. However, upon careful analysis of temperature-dependent steady state absorbance spectra, we conclude that these features are due to laser-induced thermal artifacts. We describe a simplified excited state evolution in the thin film that does not include any additional excited states. These findings have significant implications for the analysis of triplet formation, which plays a major role in the photophysics of many organic materials.

An A-D-A'-D-A-Type Narrow Bandgap Electron Acceptor Based on Selenophene-Flanked Diketopyrrolopyrrole for Sensitive Near-Infrared Photodetection

Near-infrared organic photodetectors possess great application potential in night vision, optical communication, and image sensing, but their development is limited by the lack of narrow bandgap organic semiconductors. A-D-A'-D-A-type molecules, featuring multiple intramolecular charge transfer effects, offer a robust framework for achieving near-infrared light absorption. Herein, we report a novel A-D-A'-D-A-type narrow bandgap electron acceptor named DPPSe-4Cl, which incorporates a selenophene-flanked diketopyrrolopyrrole (Se-DPP) unit as its central A' component. This molecule demonstrates exceptional near-infrared absorption properties with an absorption onset reaching 1120 nm and a low optical bandgap of 1.11 eV, owing to the strong electron-withdrawing ability and quinoidal resonance effect induced by the Se-DPP unit. By implementing a doping compensation strategy assisted by Y6 to reduce the trap density in the photoactive layer, the optimized organic photodetector based on DPPSe-4Cl exhibited efficient spectral response and remarkable sensitivity in the range of 300-1100 nm. Particularly, a specific detectivity surpassing 1012 Jones in the wavelength range of 410-1030 nm is achieved. This work offers a promising approach for developing highly sensitive visible to near-infrared broadband photodetection technology using organic semiconductors.

Promoting the Near-Infrared-II Fluorescence of Diketopyrrolopyrrole-Based Dye for In Vivo Imaging via Donor Engineering

Small-molecule dyes for fluorescence imaging in the second near-infrared region (NIR-II, 900-1880 nm) hold great promise in clinical applications. Constructing donor-acceptor-donor (D-A-D) architectures has been recognized to be a feasible strategy to achieve NIR-II fluorescence. However, the development of NIR-II dyes via such a scheme is hampered by the lack of high-performance electron acceptors and donors. Diketopyrrolopyrrole (DPP), as a classic organic optoelectronic material, enjoys strong light absorption, high fluorescence quantum yield (QY), and facile derivatization. Nevertheless, its application in the NIR-II imaging field has been hindered by its limited electron-withdrawing ability and the aggregation-caused quenching (ACQ) effect resulting from the planar structure of DPP. Herein, with DPP as an electron acceptor and through donor engineering, we have successfully designed and synthesized a DPP-based dye named T-27, in which the strong D-A interaction confers excellent NIR absorption and high-brightness NIR-II fluorescence tail emission. By strategically introducing long alkyl chains on the donor unit to increase intermolecular spacing and reduce the influence of solvent molecules, T-27 exhibits an improved anti-ACQ effect in aqueous solutions. After being encapsulated into DSPE-PEG2000, T-27 nanoparticles (NPs) show a relative NIR-II fluorescence QY of 3.4% in water, representing the highest value among the DPP-based NIR-II dyes reported to date. The outstanding photophysical properties of T-27 NPs enable multimode NIR-IIa bioimaging under 808 nm excitation. As such, the T-27 NPs can distinguish mouse femoral vein and artery and achieve cerebral vascular microscopic imaging with a penetrating depth of 800 μm, demonstrating the capability for high-resolution deep-tissue imaging. This work holds significant potential in the field of bioimaging and provides a new strategy for developing bright NIR-II dyes.

Well-Balanced Ambipolar Charge Transport of Diketopyrrolepyrrole-Based Copolymers: Organic Field-Effect Transistors and High-Voltage Logic Applications

A poly (3,6-bis(thiophen-2-yl)-2,5-bis(2-decyltetradecyl)-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione-co-(2,3-bis(phenyl)acrylonitrile)) (PDPADPP) copolymer, composed of diketopyrrolopyrrole (DPP) and a cyano (nitrile) group with a vinylene spacer linking two benzene rings, is synthesized via a palladium-catalyzed Suzuki coupling reaction. The electrical performance of PDPADPP in organic field-effect transistors (OFETs) and circuits is investigated. The OFETs based on PDPADPP exhibit typical ambipolar transport characteristics, with the as-cast OFETs demonstrating low field-effect hole and electron mobility values of 0.016 and 0.004 cm2  V-1  s-1 , respectively. However, after thermal annealing at 240 °C, the OFETs exhibit improved transport characteristics with highly balanced ambipolar transport, showing average hole and electron mobility values of 0.065 and 0.116 cm2  V-1  s-1 , respectively. To verify the application of the PDPADPP OFETs in high-voltage logic circuits, compact modeling using the industry-standard small-signal Berkeley short-channel IGFET model (BSIM) is performed, and the logic application characteristics are evaluated. The circuit simulation results demonstrate excellent logic application performance of the PDPADPP-based ambipolar transistor and illustrate that the device annealed at 240 °C exhibits ideal circuit characteristics.

Tuning the photophysical and chiroptical properties of [4]helicene-diketopyrrolopyrroles

Synthesis and functionalization of diketopyrrolo[3,4-c]pyrrole (DPP) derivatives containing chiral groups able to induce a strong chiral perturbation of the DPP core are still a challenging task. We report in this work the straightforward preparation of four bis([4]helicene)-DPP and bis([4]thiahelicene)-DPP dyes upon the condensation of 2-CN-[4](thia)helicene precursors, followed by their N-alkylation by nucleophilic substitution (compounds 9-11) or by a Mitsunobu-type strategy (compound 12). Compound 12, which contains sec-phenylethyl groups attached to the nitrogen atoms, has been obtained as (R,R) and (S,S) enantiomers. The four DPP-helicenes are luminescent in solution, while the N-benzyl (10) and N-sec-phenethyl (12) are emissive in the solid state as well. The chiroptical properties of compound 12 in solution and in the solid state indicate a strong chiral perturbation provided by the α-stereogenic centres, in spite of the stereodynamic nature of the [4]helicene flanking units.

Boosting the Thermoelectric Performance of the Doped DPP-EDOT Conjugated Polymer by Incorporating an Ionic Additive

The thermoelectric (TE) performance of organic materials is limited by the coupling of Seebeck coefficient and electrical conductivity. Herein a new strategy is reported to boost the Seebeck coefficient of conjugated polymer without significantly reducing the electrical conductivity by incorporation of an ionic additive DPPNMe₃ Br. The doped polymer PDPP-EDOT thin film exhibits high electrical conductivity up to 1377 ± 109 S cm^-1 but low Seebeck coefficient below 30 µV K^-1 and a maximum power factor of 59 ± 10 µW m^-1 K^-2 . Interestingly, incorporation of small amount (at a molar ratio of 1:30) of DPPNMe₃ Br into PDPP-EDOT results in the significant enhancement of Seebeck coefficient along with the slight decrease of electrical conductivity after doping. Consequently, the power factor (PF) is boosted to 571 ± 38 µW m^-1 K^-2 and ZT reaches 0.28 ± 0.02 at 130 °C, which is among the highest for the reported organic TE materials. Based on the theoretical calculation, it is assumed that the enhancement of TE performance for the doped PDPP-EDOT by DPPNMe₃ Br is mainly attributed to the increase of energetic disorder for PDPP-EDOT.

Non-symmetric Half-Fused B←N Coordinated Diketopyrrolopyrrole Building Block for n-type Semiconducting Polymers

The development of conjugated polymers with high semiconducting performance and high reliability is of great significance for flexible electronics. Herein, we develop a new type of electron-accepting building block; ie., non-symmetric half-fused B←N coordinated diketopyrrolopyrrole (DPP) (HBNDPP), for amorphous conjugated polymers towards flexible electronics. The rigid B←N fusion part of HBNDPP endows the resulting polymers with decent electron transport, while the non-symmetric structure of HBNDPP causes the polymer to exhibit multiple conformation isomers with flat torsional potential energies. Thus, it gets packed in an amorphous manner in solid state, ensuring good resistance to bending strain. Combined with hardness and softness, the flexible OFET devices exhibit n-type charge properties with decent mobility, good bending resistance, and good ambient stability. The preliminary study makes this building block a potential candidate for future design of conjugated materials for flexible electronic devices.

Fluorinated Dihydropentalene-1,4-Dione: A Strong Electron-Accepting Unit with Organic Semiconductor Characteristics

The development of electron-accepting units is of significant importance because the construction of donor (D)-acceptor (A) configurations is an effective strategy for tuning the electronic properties of π-conjugated systems. Although doubly fused pentagons represented by diketopyrrolopyrrole (DPP) have been used as an effective electron-accepting unit, the relatively high-lying frontier molecular orbital levels (FMOs) leave room for further improvement. We report herein the synthesis of a fluorinated dihydropentalene-1,4-dione (FPD) derivative as a strong electron-accepting unit and the development of D-A-D π-extended molecules. X-ray analyses revealed that the presence of fluorine atoms contributed to the formation of high planar structures and slipped-stacked packing. Electrochemical measurements indicated that the FPD derivatives showed relatively lower FMO energy levels than the corresponding DPP-containing derivatives. The D-A-D molecule based on terthiophene and FPD showed semiconducting responses. This study demonstrates that the FPD unit can function as a new acceptor unit for organic semiconductors.

A Hybrid Acceptor-Modulation Strategy: Fluorinated Triple-Acceptor Architecture for Significant Enhancement of Electron Transport in High-Performance Unipolar n-Type Organic Transistors

The development of unipolar n-type semiconducting polymers with electron mobility (µ_e ) over 5 cm²  V^-1  s^-1 remains a massive challenge in organic semiconductors. Diketopyrrolopyrrole (DPP) has proven to be a successful unit for high-performance p-type and ambipolar polymers. However, DPP's moderate electron-accepting capability leads to the shallow frontier molecular orbital (FMO) levels of the resultant polymers and hence limit the µ_e in unipolar n-type organic transistors. Herein, this issue has been addressed by using a hybrid acceptor-modulation strategy based on DPP-containing "fluorinated triple-acceptor architecture", namely DPP-difluorobenzothiadiazole-DPP (DFB). Compared with DFB's non-fluorinated counterpart, DFB features deeper FMO levels and a shape-persistent framework. Therefore, a series of DFB-based polymers demonstrate planar backbones and lowered FMO levels by ≈0.10 to 0.25 eV versus that of the control polymer. Intriguingly, all DFB-polymers exhibit excellent unipolar n-type transistor performances. Notably, a full-locked backbone conformation and high crystallinity with crystalline coherence length of 524 Å are observed for pDFB-TF, accounting for its high µ_e of 5.04 cm²  V^-1  s^-1 , which is the highest µ_e value for DPP-based unipolar n-type polymers reported to date. This work demonstrates that the strategy of "fluorinated triple-acceptor architecture" opens a new path towards high-performance unipolar n-type semiconducting polymers.

Disentangling Excimer Emission from Chiral Induction in Nanoscale Helical Silica Scaffolds Bearing Achiral Chromophores

The synthesis and characterization of diketopyrrolopyrroles and perylenemonoimidodiesters linked to a substituted benzoic acid in the ortho, meta, and para positions, are reported. Grafting of these dyes on the surface of chiral silica nanohelices is used to probe how the morphology of the platform at the mesoscopic level affects the induction of chiroptical properties onto achiral molecular chromophores. The grafted structures are weakly (diketopyrrolopyrroles) or strongly (perylenemonoimidodiesters) emissive, exhibiting both locally-excited state emission and a broad, structureless emission assigned to excimers. The dissymmetry factors obtained using circular dichroism highlight optimized supramolecular organization between the chromophores for enhancing the chiroptical properties of the system. In the ortho- derivatives, poor organization due to steric hindrance is reflected in a low density of chromophores on walls of the silica-nanostructures (<0.1 vs. >0.3 and up to 0.6 molecules/nm² for the ortho and meta or para derivatives, respectively) and lower g_abs values than in the other derivatives (g_abs <2×10^-5 vs 6×10^-5 for the ortho and para derivatives, respectively). The para derivatives presented a better organization and increased values of g_abs . All grafted chromophores evidence varying degrees of excimer emission which was not found to directly correlate to their grafting density.

Carbazole and Diketopyrrolopyrrole-Based D-A π-Conjugated Oligomers Accessed via Direct C-H Arylation for Opto-Electronic Property and Performance Study

Five carbazole and diketopyrrolopyrrole-based donor-acceptor (D-A) new π-conjugated oligomers (π-COs) with gradually elongated lengths are facilely synthesized via a single pot of direct C-H arylation with merits of atom- and step-economy. The structure-property-performance correlations of these π-COs and their parent polymer are studied in detail by opto-electronic characterizations and bulk heterojunction (BHJ) organic photovoltaic (OPV) devices. It is found that the π-COs having longer lengths enable better performance in OPVs owing to the enhanced intermolecular interaction with the elongation of the conjugations. The above results not only highlight the powerful synthetic strategy here provided, but also reveal that π-COs with unique properties might find promising application in OPVs.

Hyperbranched Diketopyrrolopyrrole-based Polymers Constructed via Linear Side-Chains towards Organic Field-Effect Transistors

Conjugated polymers with high charge mobilities have drawn increasing attention in organic field-effect transistors (OFETs) in recent years. However, OFETs of conjugated polymers with high mobility and good device stability remain a challenge. In this article, we report a hyperbranched polymer approach to improve the charge mobility and device stability. Three hyperbranched diketopyrrolopyrrole-based polymers were designed and synthesized via linear alkyl side-chain linkers. The results show that 2D topological hyperbranched polymers form stable thin film microstructures, and thus improve the device stability, since the conjugated moiety is interconnected by linear alkyl chain. Besides, the incorporation of linear alkyl chain instead of branching alkyl one reduce steric hindrance, and improve the microstructure ordering as well as the charge mobility. Bar-coated OFETs result demonstrates that the devices mobilities and operational stabilities (bias stability and bending resistance) are both improved. All these indicate that hyperbranched polymer is a potential candidate for future application.

Complete Set of Diketopyrrolopyrrole Centrosymmetrical Cofacial Stacked Pairs

Stacked centrosymmetrical dimers and simultaneously H-bonded and stacked hexamers of thiophene-substituted diketopyrrolopyrrole (ThDPP) were studied using DFT as models for crystals with slipped-stacked molecules in 1D columns. Eight stacked dimer arrangements were found, six of which are driven by the minimisation of electron repulsion and realised by placing the partially negatively charged atoms of the diketopyrrolopyrrole rings below the centre of an adjancent thiophene ring. Four of these stacks are related to N,N'-diacylated derivative. An analogous set of eight stacks was discovered computationally for phenyl-substituted DPP (PhDPP), four of which are known among H-bonded DPP pigments, and one more among N,N'-dialkylated PhDPP derivatives. The results shed more light on the mechanisms that drive the formation of stacks between nonaromatic (DPP) and aromatic (Th, Ph) rings. The excitation energies of the lowest four singlet states computed by TD DFT enabled excitonic coupling and energy separation between Frenkel-resonsnce-type and charge-transfer states to be established, depending on the equilibrium stack geometry.

Novel Thienyl DPP derivatives Functionalized with Terminal Electron-Acceptor Groups: Synthesis, Optical Properties and OFET Performance

Three novel diketopyrrolopyrrole (DPP) based small molecules have been synthesized and characterized in terms of their chemical-physical, electrochemical and electrical properties. All the molecules consist of a central DPP electron acceptor core symmetrically functionalized with donor bi-thienyl moieties and flanked in the terminal positions by three different auxiliary electron-acceptor groups. This kind of molecular structure, characterized by an alternation of electron acceptor and donor groups, was purposely designed to provide a significant absorption at the longer wavelengths of the visible spectrum: when analysed as thin films, in fact, the dyes absorb well over 800 nm and exhibit a narrow optical bandgap down to 1.28 eV. A detailed DFT analysis provides useful information on the electronic structure of the dyes and on the features of the main optical transitions. Organic field-effect transistors (OFETs) have been fabricated by depositing the DPP dyes as active layers from solution: the different end-functionalization of the dyes had an effect on the charge-transport properties with two of the dyes acting as n-type semiconductors (electron mobility up to 4.4 ⋅ 10^-2  cm² /V ⋅ s) and the third one as a p-type semiconductor (hole mobility up to 2.3 ⋅ 10^-3  cm² /V ⋅ s). Interestingly, well-balanced ambipolar transistors were achieved by blending the most performant n-type and p-type dyes with hole and electron mobility in the order of 10^-3  cm² /V ⋅ s.

An Enhanced Photothermal Therapeutic Iridium Hybrid Platform Reversing the Tumor Hypoxic Microenvironment

As hypoxia is closely associated with tumor progression, proliferation, invasion, metastasis, and strong resistance to therapy, regulating and overcoming the hypoxia tumor microenvironment are two increasingly important aspects of tumor treatment. Herein, we report a phototherapeutic platform that uses the organic photosensitizer diketopyrrolopyrrole (DPP) derivative and inorganic iridium salts (IrCl₃) with photothermal activity and the capacity to decompose H₂O₂ efficiently. The characterization of their photophysical properties proved that DPP-Ir nanoparticles are capable of remarkable near-infrared (NIR) absorption, and compared to DPP nanoparticles, the photothermal conversion efficiency (PCE) increases from 42.1% in DPP nanoparticles to 67.0% in DPP-Ir nanoparticles. The hybrid nanoparticles utilize the catalytic decomposition of endogenous H₂O₂ to produce oxygen for the downregulation of the hypoxia-inducible factor 1 subunit alpha (HIF-1α) protein, which could reverse the tumor hypoxic microenvironment. Benefiting from the excellent optical properties and good biocompatibility, the hybrid platform exhibits efficient photothermal therapeutic effects as well as good biological safety. In conclusion, such a hybrid platform could improve photothermal therapy against cancer.

Effects of the Polarity and Bulkiness of End-Functionalized Side Chains on the Charge Transport of Dicyanovinyl-End-Capped Diketopyrrolopyrrole-Based n-Type Small Molecules

When designing organic semiconductors, side-chain engineering is as important as modifying the conjugated backbone, which has a significant impact on molecular ordering, morphology, and thus electronic device performance. We have developed three dicyanovinyl-end-capped donor-acceptor diketopyrrolopyrrole-based n-type small molecules (C2C9CN, SiC4CN, and EH4PCN) bearing an identical length of alkyl spacer yet different end-functionalized side chains (i.e., alkyl-, siloxane-, and phosphonate-end pendants). The effects of the end-functionalized side chains on the intrinsic molecular properties, microstructure, and charge transport of the small-molecule series were investigated. In comparison with the alkyl-end side chains, incorporating siloxane-end side chains into the backbone facilitates 2D edge-on oriented high intergrain connectivity/crystallinity and compatibility with the substrate surface, whereas the phosphonate-end analogues have an adverse effect on the film-forming quality due to high polarity. Thereby, an organic field-effect transistor fabricated by SiC4CN shows the best electron mobility up to 1.59 × 10-1 cm2 V-1 s-1 along with a high current on/off ratio >105. This study contributes to our understanding of the role of the end-functionalized side chains (e.g., the effects of polarity and bulkiness of the end groups) for the development of high-performance semiconductors.

Single-Molecule Charge-Transport Modulation Induced by Steric Effects of Side Alkyl Chains

The experimental investigation of side-chain effects on intramolecular charge transport in π-conjugated molecules is essential but remains challenging. Herein, the dependence of intra-molecular conductance on the nature of branching alkyl chains is investigated through a combination of the scanning tunneling microscope break junction (STM-BJ) technique and density functional theory. Three thiophene-flanked diketopyrrolopyrrole (DPP) derivatives with different branching alkyl chains (isopentane, 3-methylheptane, and 9-methylnonadecane) are used with phenylthiomethyl groups as the anchoring groups. The results of single-molecule conductance measurements show that as the alkyl chain becomes longer, the torsional angles between the aromatic rings increase due to steric crowding, and therefore, the molecular conductance of DPP decreases due to reduction in conjugation. Both theoretical simulations and ¹ H NMR spectra demonstrate that the planarity of the DPPs is directly reduced after introducing longer branching alkyl chains, which leads to a reduced conductance. This work indicates that the effect of the insulating side chain on the single-molecule conductance cannot be neglected, which should be considered for the design of future organic semiconducting materials.

A Convenient Synthesis of Diketopyrrolopyrrole Dyes

Diketopyrrolo[3,4-c]pyrroles (DPP) are high-performance organic optoelectronic materials. They have applications in solar cells, fluorescent probes, bioimaging, photodynamic/photothermal therapy, and in many other areas. This article reports a convenient two-step synthesis of various DPP dyes from Pigment Red 254, an inexpensive commercial pigment. The synthesis includes a Suzuki-Miyaura cross-coupling reaction of a bis(4-chlorophenyl)DPP derivative with aryl and hetaryl boronic acids under mild reaction conditions. The new dyes show large Stokes shifts and high fluorescence quantum yields, important features for their potential use in technical and biological applications.

A Small-Molecule Diketopyrrolopyrrole-Based Dye for in vivo NIR-IIa Fluorescence Bioimaging

Organic small-molecule fluorophores with near-infrared IIa (NIR-IIa) emission have great potential in pre-clinical detection and inoperative imaging due to the high-spatial resolution and deep penetration. However, developments of the NIR-IIa fluorophores are still facing considerable challenges. In this work, a series of diketopyrrolopyrrole (DPP)-based fluorophores were designed and synthesized. Subsequently, nanomaterial T25@F127 with significant NIR-IIa emission properties was rationally prepared by encapsulating DPP-based fluorophore T25, and was selected for fluorescence angiography and cerebral vascular microscopic imaging with nearly 800 μm penetrating depth and excellent signal-background ratio of 4.07 and 2.26 (at 250 and 400 μm), respectively. Furthermore, the nanomaterial T25@cRGD with tumor targeting ability can image tiny metastatic tumor on intestine with a small size of 0.3 mm×1.0 mm and high-spatial resolution (SBR=3.84). This study demonstrates that the nanomaterials which encapsulated T25 behave as excellent NIR-IIa fluorescence imaging agents and have a great potential for in vivo biological application.

Janus Pyrrolopyrrole Aza-dipyrrin: Hydrogen-Bonded Assemblies and Slow Magnetic Relaxation of the Cobalt(II) Complex in the Solid State

A novel pyrrolopyrrole azadipyrrin (Janus-PPAD) with Janus duality was synthesized by a Schiff base-forming reaction of diketopyrrolopyrrole. The orthogonal interactions of the hydrogen-bonding ketopyrrole and metal-coordinating azadipyrrin moieties in Janus-PPAD enabled the metal ions to be arranged at regular intervals: zinc(II) and cobalt(II) coordination provided metal-coordinated Janus-PPAD dimers, which can subsequently form hydrogen-bonded one-dimensional arrays both in solution and in the solid state. The supramolecular assembly of the zinc(II) complex in solution was investigated by ¹ H NMR spectroscopy based on the isodesmic model, in which a binding constant for the elongation of assemblies is constant. Owing to the tetrahedral coordination, in the solid state, the cobalt(II) complex exhibited a slow magnetic relaxation due to the negative D value of -27.1 cm^-1 with an effective relaxation energy barrier U_eff of 38.0 cm^-1 . The effect of magnetic dilution on the relaxation behavior is discussed. The relaxation mechanism at low temperature was analyzed by considering spin lattice interactions and quantum tunneling effects. The easy-axis magnetic anisotropy was confirmed, and the relevant wave functions were obtained by ab initio CASSCF calculations.

A-π-D-π-A-Based Small Molecules for OTFTs Containing Diketopyrrolopyrrole as Acceptor Units

A-π-D-π-A-based small molecules 6,6′-((thiophene-2,5-diylbis(ethyne-2,1-diyl))bis(thiophene-5,2-diyl))bis(2,5-bis(2-ethylhexyl)-3-(thiophen-2-yl)-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione) (TDPP-T) and 6,6′-(((2,3-dihydrothieno[3,4-b][1,4]dioxine-5,7-diyl)bis(ethyne-2,1-diyl))bis(thiophene-5,2-diyl))bis(2,5-bis(2-ethylhexyl)-3-(thiophen-2-yl)-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione) (TDPP-EDOT) have been designed and synthesized. The diketopyrrolopyrrole acts as an electron acceptor, while the thiophene or 3,4-ethylenedioxythiophene acts as an electron donor. The donor–acceptor groups are connected by an ethynyl bridge to further enhance the conjugation. The optoelectronics, electrochemical, and thermal properties have been investigated. Organic thin film transistor (OTFT) devices prepared from TDPP-T and TDPP-EDOT have shown p-type mobility. In as cast films, TDPP-T and TDPP-EDOT have shown a hole mobility of 5.44 × 10⁻⁶ cm² V⁻¹ s⁻¹ and 4.13 × 10⁻⁶ cm² V⁻¹ s⁻¹, respectively. The increase in the mobility of TDPP-T and TDPP-EDOT OTFT devices was observed after annealing at 150 °C, after which the mobilities were 3.11 × 10⁻⁴ cm² V⁻¹ s⁻¹ and 2.63 × 10⁻⁴ cm² V⁻¹ s⁻¹, respectively.

Development of Diketopyrrolopyrrole-Based Smart Inks by Substituting Ionic Pendants and Engineering Molecular Packing Structures

A series of diketopyrrolopyrrole (DPP) luminogen amphiphiles were newly designed and synthesized by a single-step anionic exchange reaction for controlling the photoluminescence properties in both solution and solid states. Multicolor emission in response to thermal, mechanical, and chemical stimuli was successfully demonstrated by engineering well-defined supramolecular assemblies. Phase transformation from the metastable amorphous solid to the stable orthorhombic crystal of [DP-Im][Br] provided the reversibly patternable light emission. Self-organization into the smectic crystalline phase of [DP-Im][TFSI] allowed us to show the linearly polarized light emission. By simultaneously applying [DP-Im][Br] and [DP-Im][TFSI], we demonstrated the fabrication of smart sensors for packaging of food or vaccines that can detect thermal attacks.

Electrochemical Evaluation of Diketopyrrolopyrrole Derivatives for Nonaqueous Redox Flow Batteries

Redox flow batteries (RFBs) employing nonaqueous electrolytes could potentially operate at much higher cell voltages, and therefore afford higher energy and power densities, than RFBs employing aqueous electrolytes. The development of such high-voltage nonaqueous RFBs requires anolytes that are electrochemically stable, especially in the presence of traces of oxygen and/or moisture. The inherent atmospheric reactivity of anolytes mandates judicious molecular design with high electron affinity and electrochemical stability. In this study, diketopyrrolopyrrole (DPP)-based TDPP-Hex-CN₄ is proposed as a stable redox-active molecule for anolytes in nonaqueous organic RFBs. We demonstrate organic RFBs using TDPP-Hex-CN₄ as anolyte with unisol blue (UB) 1,4-bis(isopropylamino)anthraquinone and 1,4-di-tert-butyl-2,5-bis(2-methoxyethoxy)benzene (DBBB) as catholytes. Cyclic voltammetry measurements with scans repeated over 200 cycles were performed to establish the electrochemical stability of the redox pairs. Symmetric flow-cell studies show that TDPP-Hex-CN₄ exhibits stable capacity up to 700 cycles. Redox flow cells employing TDPP-Hex-CN₄ /UB and TDPP-Hex-CN₄ /DBBB as redox pairs demonstrate that DPP derivatives are propitious materials for anolytes in all organic nonaqueous RFBs.

New Synthetic Approaches to N-Aryl and π-Expanded Diketopyrrolopyrroles as New Building Blocks for Organic Optoelectronic Materials

Diketopyrrolopyrrole (DPP) as a building block has been intensively investigated for organic semiconductors and light emitting materials. The synthesis of N-aryl DPPs remains challenging. Herein, we firstly report a new easily handled synthetic method toward N-aryl DPPs through H-DPP with diaryliodonium salt in the presence of CuI, which shows broad reaction scope. Sixteen N-aryl DPPs, including phenyl, furan and thiophene as flanking aromatic groups, were synthesized with yields up to 78 %. These N-aryl DPPs are fluorescent in both solutions and solid states, with quantum yields up to 96 % and 40 %, respectively. Moreover, we show that the reaction between H-DPP and diaryliodonium salt can lead to π-expanded DPPs by using Pd(OAc)₂ as catalyst. Nine π-expanded DPPs were obtained in 27-61 % yields. These π-expanded DPPs exhibit good semiconducting properties with hole mobility of 0.71 cm²  V^-1  s^-1 , demonstrating that they are useful building blocks for high performance organic semiconductors.

Side-Chain Engineering of Diketopyrrolopyrrole-Based Hole-Transport Materials to Realize High-Efficiency Perovskite Solar Cells

The design and synthesis of a stable and efficient hole-transport material (HTM) for perovskite solar cells (PSCs) are one of the most demanding research areas. At present, 2,2',7,7'-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9'-spirobifluorene (spiro-MeOTAD) is a commonly used HTM in the fabrication of high-efficiency PSCs; however, its complicated synthesis, addition of a dopant in order to realize the best efficiency, and high cost are major challenges for the further development of PSCs. Herein, various diketopyrrolopyrrole-based small molecules were synthesized with the same backbone but distinct alkyl side-chain substituents (i.e., 2-ethylhexyl-, n-hexyl-, ((methoxyethoxy)ethoxy)ethyl-, and (2-((2-methoxyethoxy)ethoxy)ethyl)acetamide, designated as D-1, D-2, D-3, and D-4, respectively) as HTMs. The variation in the alkyl chain has shown obvious effects on the optical and electrochemical properties as well as on the molecular packing and film-forming ability. Consequently, the power conversion efficiency (PCE) of the PSC under one sun illumination (100 mW cm^-2) is shown to increase in the order of D-1 (8.32%) < D-2 (11.12%) < D-3 (12.05%) < D-4 (17.64%). Various characterization techniques reveal that the superior performance of D-4 can be ascribed to the well-aligned highest occupied molecular orbital energy level with the counter electrode, the more compact π-π stacking with a higher coherence length, and the excellent hole mobility of 1.09 × 10^-3 cm² V^-1 s^-1, thus providing excellent energetics for effective charge transport with minimal charge-carrier recombination. Furthermore, the addition of the dopant Li-TFSI in D-4 is shown to deliver a remarkable PCE of 20.19%, along with a short-circuit current density (J_SC), open-circuit voltage (V_OC), and fill factor (FF) of 22.94 mA cm^-2, 1.14 V, and 73.87%, respectively, and superior stability compared to that of other HTMs. These results demonstrate the effectiveness of side-chain engineering for tailoring the properties of HTMs, thus offering new design tactics to fabricate for the synthesis of highly efficient and stable HTMs for PSCs.

Synthesis of Novel 3,6-Dithienyl Diketopyrrolopyrrole Dyes by Direct C‒H Arylation

Direct C-H arylation coupling is potentially a more economical and sustainable process than conventional cross-coupling. However, this method has found limited application in the synthesis of organic dyes for dye-sensitized solar cells. Although direct C-H arylation is not an universal solution to any cross-coupling reactions, it efficiently complements conventional sp²−sp² bond formation and can provide shorter and more efficient routes to diketopyrrolopyrrole dyes. Here, we have applied palladium catalyzed direct C-H arylation in the synthesis of five new 3,6-dithienyl diketopyrrolopyrrole dyes. All prepared sensitizers display broad absorption from 350 nm up to 800 nm with high molar extinction coefficients. The dye-sensitized solar cells based on these dyes exhibit a power conversion efficiency in the range of 2.9 to 3.4%.

Design and Synthesis of Air-Stable p-Channel-Conjugated Polymers for High Signal-to-Drift Nitrogen Dioxide and Ammonia Sensing

The development of high-performance-conjugated polymer-based gas sensors involves detailed structural tailoring such that high sensitivities are achieved without compromising the stability of the fabricated devices. In this work, we systematically developed a series of diketopyrrolopyrrole (DPP)-based polymer semiconductors by modifying the polymer backbone to achieve and rationalize enhancements in gas sensitivities and electronic stability in air. NO₂- and NH₃-responsive polymer-based organic field-effect transistors (OFETs) are described with improved air stability compared to all-thiophene conjugated polymers. Five DPP-fluorene-based polymers were synthesized and compared to two control polymers and used as active layers to detect a concentration of NO₂ at least as low as 0.5 ppm. The hypothesis that the less electron-donating fluorene main-chain subunit would lead to increased signal/drift compared to thiophene and carbazole subunits was tested. The sensitivities exhibited a bias voltage-dependent behavior. The proportional on-current change of OFETs using a dithienyl DPP-fluorene polymer reached ∼614% for an exposure to 20 ppm of NO₂ for 5 min, testing at a bias voltage of -33 V, among the higher reported NO₂ sensitivities for conjugated polymers. Electronic and morphological studies reveal that introduction of the fluorene unit in the DPP backbone decreases the ease of backbone oxidation and induces traps in the thin films. The combination of thin-film morphology and oxidation potentials governs the gas-absorbing properties of these materials. The ratio of responses on exposure to NO₂ and NH₃ compared to drifts while taking the device through repeated gate voltage sweeps is the highest for two polymers incorporating electron-donating linkers connecting the DPP and thiophene units in the backbone, in this category of organic semiconductors. The responses to NO₂ were much larger than that to NH₃, indicating increased susceptibility to oxidizing vs reducing gases, and that the capability of oxidizing gases to induce additional charge density has a more dramatic electronic effect than when reducing gases create traps. This work demonstrates the capability of achieving improved stability with the retention of high sensitivity in conjugated polymer-based OFET sensors by modulating redox and morphological properties of polymer semiconductors by structural control.

Chiral Diketopyrrolopyrrole-Helicene Polymer With Efficient Red Circularly Polarized Luminescence

Chiral diketopyrrolopyrrole (DPP)-helicene polymers were synthesized to develop efficient red circularly polarized (CP) light emitters. These original chiral dyes display intense electronic circular dichroism (ECD) and CP luminescence (CPL) in the far-red spectral region owing to the presence of excitonic coupling between achiral DPPs within the chiral environment of the polymeric structure. This work affords an interesting example illustrating the potential of π-conjugated helical polymers for chiral optoelectronic applications.

Self-Assembly of Board-Shaped Diketopyrrolopyrrole and Isoindigo Mesogens into Columnar π-π Stacks

Diketopyrrolopyrrole and isoindigo are commercially important dyes that have recently found broad application as electron acceptor and light-absorbing groups in organic semiconductors. Their self-assembly into specific supramolecular structures to control optoelectronic properties has been hampered by limited options for substitution and their high propensity for crystallization. Reported here is a molecular design that directs self-assembly into previously elusive columnar mesophases of π-π stacking cores. Although attachment of bis(trisoctyloxyphenyl)-1,3,5-triazine groups to both ends of diketopyrrolopyrrole-thiophene and isoindigo cores generated mesomorphic dyes of similar overall shapes and dimensions, distinct differences in their mesomorphism and optoelectronic properties were observed.

n-Type Thin-Film Transistors Based on Diketopyrrolopyrrole Derivatives: Role of Siloxane Side Chains and Electron-Withdrawing Substituents

The physical properties, packing, morphology, and semiconducting performance of a planar π-conjugated system can be effectively modified by introducing side chains and substituent groups, both of which can be complementary to the π framework in changing the intermolecular association, frontier molecular orbital energy, optical band gap, and others. We herein show that installation of end-capped electron-withdrawing groups (EWGs), such as dicyanovinyl (-DCV), 3-ethylrhodanine (-RD), and 2-(3-oxo-indan-1-ylidene)-malononitrile (-INCN), together with siloxane side chains to the backbones of dithienyldiketopyrrolopyrrole (DPPT), such as DPPT-Si-DCV, DPPT-Si-RD, and DPPT-Si-INCN, can greatly improve its solubility, air stability, and film morphology to serve as an n-channel in thin-film transistor fabrication. The EWGs attached to the DPPT core narrowed the optical band gap (E_g^opt) and changed the highest occupied molecular orbital and the lowest unoccupied molecular orbital energies (E_HOMO and E_LUMO), making them suitable for n-channel field-effect transistor (FET) applications. The benefits of introducing siloxane side chains to the DPPT core include enhanced solubility, low crystallization barrier, enantiotropic phase behavior, and much improved FET performance. The DPPT-Si-INCN film displayed low-lying HOMO (-5.82 eV) and LUMO (-4.60 eV) energy levels and an optical band gap as low as 1.22 eV, all of which suggest that this derivative can be quite resistant toward aerial oxidation. Thin films of these derivatives were prepared by the solution-shear method. A comparison of the solution-sheared films indicated that the molecular packing motif of DPPT-Si-INCN film was somehow different from that of DPPT-Si-DCV and DPPT-Si-RD, in which the π-π stacking tended to align orthogonally to the shearing direction. This specific π-π stacking alignment could have an impact on the electron mobility (μ_e) values in transistors based on the solution-sheared films.

Influence of Backbone Regioregularity on High-Mobility Conjugated Polymers Based on Alkylated Dithienylacrylonitrile

We designed and synthesized two donor-acceptor type conjugated polymers, the regioirregular polymer RI-PDPP-CNTVT-6 and its regioregular counterpart RR-PDPP-CNTVT-6, based on diketopyrrolopyrrole (DPP) and alkylated dithienylacrylonitrile (CNTVT) units. Among them, the 2-decyltetradecyl side chain on the DPP acceptor unit and the hexyl side chain on the CNTVT donor unit were used to ensure enough solubility for them. The backbone regioregularity was used to tune electronic structures and carrier transport of the conjugated system. The two conjugated polymers were characterized for their thermal, photophysical, electrochemical, and solution-processable properties, thin-film microstructures, and morphologies. The top-gate bottom-contact configuration organic field-effect transistor (OFET) devices based on these two conjugated polymers showed excellent ambipolar performances. Remarkably, the regioirregular polymer RI-PDPP-CNTVT-6 exhibited higher charge-carrier mobilities than the regioregular counterpart polymer RR-PDPP-CNTVT-6 did, as their highest hole/electron mobilities (μ_hmax/μ_emax) were 1.48/1.27 and 0.48/0.052 cm² V^-1 s^-1, respectively. Moreover, the influence of backbone regioregularity on its thermal stability, electrochemical and photophysical properties, solution processability, and charge-carrier mobility was intensively studied. Our results afforded a promising pathway toward the development of excellent ambipolar OFETs with high performance, good solution processability, and thermal stability.

Fused Bithiophene Imide Oligomer and Diketopyrrolopyrrole Copolymers for n-Type Thin-Film Transistors

Diketopyrrolopyrrole (DPP)-based copolymers have received considerable attention as promising semiconducting materials for high-performance organic thin-film transistors (OTFTs). However, these polymers typically exhibit p-type or ambipolar charge-transporting characteristics in OTFTs due to their high-lying highest occupied molecular orbital (HOMO) energy levels. In this work, a new series of DPP-based n-type polymers have been developed by incorporating fused bithiophene imide oligomers (BTIn) into DPP polymers. The resulting copolymers BTIn-DPP show narrow band gaps as low as 1.27 eV and gradually down-shifted frontier molecular orbital energy levels upon the increment of imide group number. Benefiting from the coplanar backbone conformation, well-delocalized π-system, and favorable polymer chain packing, the optimal polymer in the series shows promising n-type charge transport with an electron mobility up to 0.48 cm² V^-1 s^-1 in OTFTs, which is among the highest values for the DPP-based n-type polymers reported to date. The results demonstrate that incorporating fused bithiophene imide oligomers into polymers can serve as a promising strategy for constructing high-performance n-type polymeric semiconductors.

Electrohydrodynamic-Jet (EHD)-Printed Diketopyrrolopyroole-Based Copolymer for OFETs and Circuit Applications

We report the employment of an electrohydrodynamic-jet (EHD)-printed diketopyrrolopyrrole-based copolymer (P-29-DPPDTSE) as the active layer of fabricated organic field-effect transistors (OFETs) and circuits. The device produced at optimal conditions showed a field-effect mobility value of 0.45 cm²/(Vs). The morphologies of the printed P-29-DPPDTSE samples were determined by performing optical microscopy, X-ray diffraction, and atomic force microscopy experiments. In addition, numerical circuit simulations of the optimal printed P-29-DPPDTSE OFETs were done in order to observe how well they would perform in a high-voltage logic circuit application. The optimal printed P-29-DPPDTSE OFET showed a 0.5 kHz inverter frequency and 1.2 kHz ring oscillator frequency at a 40 V supply condition, indicating the feasibility of its use in a logic circuit application at high voltage.

Rational Design of BODIPY-Diketopyrrolopyrrole Conjugated Polymers for Photothermal Tumor Ablation

Conjugated polymers (CPs) have drawn growing attention in cancer phototherapy and imaging due to their large extinction coefficients, robust photostability, and good biocompatibility. Herein, we propose a new type of photothermal therapy materials on the basis of BODIPY-diketopyrrolopyrrole CPs, where the number of methyl substituents at the β and β' positions on BODIPYs is variable, allowing us to investigate the interplay between the structure of the monomers and the related properties of CPs. Combining the experimental data with theoretical calculations, we concluded that with the decrease of the number of methyl moieties on the β and β' positions of BODIPY, the polymerization degree and the solubility of the obtained CPs improved and the polymeric spatial planarization and degrees of conjugation increased, inducing the bathochromic shift of absorption, which resulted in the absorption spectra getting closer to the near-infrared region and more conducive to the application of the conjugated polymers in vivo. Afterward, the CP nanoparticles were constructed and their photothermal activity in cancer therapy was validated by a series of in vitro and in vivo experiments. In this paper, we provide a new way to manipulate properties of CPs with great potential in photothermal therapy through structural engineering.

Fluoro-Modulated Molecular Geometry in Diketopyrrolopyrrole-Based Low-Bandgap Copolymers for Tuning the Photovoltaic Performance

Fluorination of conjugated polymers is an effective strategy to tune the energy levels for obtaining high power conversion efficiency (PCE) in organic solar cells. In this work, we have developed fluoro-modulated molecular geometries in diketopyrrolopyrrole based low-bandgap copolymers. In these polymers, planar conformation can be locked by intramolecular non-covalent interaction (intramolecular supramolecular interaction) between the sulfur atoms and the introduced F atoms (F···S interaction). By varying the fluorinated moieties, such a planarity can be disturbed and the molecular geometry is tuned. As a result, the polymer' properties can be modulated, including the ultraviolet-visible absorption spectrum to become broaden, charge mobility to be enhanced, open-circuit voltage (V _oc) and short-circuited current (J _sc) to be elevated, and thus photovoltaic performance to be improved. The photovoltaic device based on PCFB, one of the fluorinated terpolymers, exhibited a high PCE near 8.5% with simultaneously enhanced V _oc and J _sc relative to the non-fluorinated one (PCB).

Three differently coloured polymorphs of 3,6-bis(4-chlorophenyl)-2,5-dipropyl-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione

In this paper, the conformational polymorphism of a chlorinated diketopyrrolopyrrole (DPP) dye having flexible substituents in a non-hydrogen-bonding system is reported. The propyl-substituted DPP derivative (PR3C) has three polymorphic forms, each showing a different colour (red, orange and yellow). All polymorphs could be obtained concomitantly under various crystallization conditions. The results of the crystal structure analysis indicate that PR3C adopts different conformations in each polymorph. The packing effect caused by the difference in the arrangement of neighbouring molecules was found to play an important role in the occurrence of the observed polymorphism. The thermodynamic stability relationship between the three polymorphs was identified by thermal analysis and indicates that the yellow polymorph is the thermally stable form. The results indicate that the yellow form and orange form are enantiotropically related, and the other polymorph is monotropically related to the others.

Preparation and Physical Characterization of Pyrene and Pyrrolo[3,4-c]pyrrole-1,4-dione-Based Copolymers

Two narrow band-gap copolymers consisting of 2,7-bis(5-(trimethylstannyl)thiophen-2-yl)-4,5,9,10-tetrakis(2-ethylhexyloxy)-pyrene (M1) as an electron-rich unit and diketopyrrolopyrrole (DPP) as an electron-deficient unit have been synthesized and characterized for polymer solar cells. The two polymers were prepared by Stille coupling reactions. Two solubilizing alkyl chains (ethylhexyl and octlydodecyl) were attached to the DPP unit in order to evaluate their impact upon the optical and electrochemical characteristics of the two polymers. Poly[4,5,9,10-tetrakis[(2-ethylhexyl)oxy]pyrene-alt-3,6-bis(thiophen-2-yl)-2,5- bis(2-octyldodecyl)pyrrole[3,4-c]pyrrole- 1,4(2H,5H)-dione] (PPEHDT-DPPODo ) and poly[4,5,9,10-tetrakis((2-ethylhexyl)oxy)pyren-alt-3,6-bis(thiophen-2-yl)-2,5-bis(2-ethylhexyl)pyrrole[3,4-c]pyrrole-1,4(2H,5H)-dione] (PPEHDT-DPPEH ) exhibited high thermal stability with decomposition temperatures over 300 °C. Optical properties showed that PPEHDT-DPPODo and PPEHDT-DPPEH have optical band gaps of around 1.40 eV. It is believed that both polymers adopt high planar structures in the thin film, leading to more electronic conjugation along the backbone of the conjugated polymers. Powder X-ray diffraction revealed that PPEHDT-DPPODo and PPEHDT-DPPEH seem to have an amorphous nature. The HOMO energy levels of the two polymers are clearly affected by changing alkyl chains. The HOMO levels of PPEHDT-DPPODo and PPEHDT-DPPEH were found to be at -5.27 and -5.38 eV, respectively. PPEHDT-DPPODo showed a HOMO energy level approximately 0.11 eV shallower than that of PPEHDT-DPPEH , which is probably a consequence of attaching a larger alkyl chain to the DPP moiety reducing its electron accepting ability.

Control of Crystallite Orientation in Diketopyrrolopyrrole-Based Semiconducting Polymers via Tuning of Intermolecular Interactions

Numerous previous studies have focused on the notion that semiconducting polymers with an edge-on dominant orientation are advantageous for horizontal charge transport, whereas polymers with a face-on dominant orientation are advantageous for vertical charge transport, since the crystallite orientation determines the π-π stacking direction, which in turn affects the interchain charge transport direction. Here, we report that the crystallite orientation is dependent on the intermolecular interactions in the semiconducting polymer. In this study, we control the intermolecular interactions in a donor-acceptor (D-A) semiconducting polymer via side chain engineering. To perform side chain engineering, we use two different polymers: one with side chains on only A units (PDPP-B) and the other with side chains on both D and A units (PDPP-C8). We observe that PDPP-C8 is characterized by weaker intermolecular interactions due to the additional side chains on D units. A morphological analysis reveals that PDPP-B and PDPP-C8 films have microstructures that are characterized by edge-on and face-on dominant orientations, respectively. Therefore, we demonstrate that our strategies effectively control intermolecular interactions and, consequently, the crystallite orientation. Finally, we compare the vertical and horizontal mobilities of both polymer films. These results show that the crystallite orientation has significant influence on charge transport behaviors.

Panchromatic Ternary Organic Solar Cells with Porphyrin Dimers and Absorption-Complementary Benzodithiophene-based Small Molecules

Diketopyrrolopyrrole-ethynylene-bridged porphyrin dimers are capped with electron-deficient 3-ethylrhodanine (A₂) via a π-bridge of phenylene ethynylene, affording two new acceptor-donor-acceptor structural porphyrin dimers (DPP-2TTP and DPP-2TP) with strong absorption in ranges of 400-550 nm (Soret bands) and 700-900 nm (Q bands). Their intrinsic absorption deficiency between the Soret and Q bands could be perfectly compensated by a wide-bandgap small molecule DR3TBDTTF (D*) with absorption at 500-700 nm. Impressively, the optimal ternary device based on the blend films of DPP-2TPP, DR3TBDTTF (20 wt %), and PC₇₁BM shows a PCE of 11.15%, whereas the binary devices based on DPP-2TTP/PC₇₁BM and DPP-2TP/PC₇₁BM blend films exhibit PCEs of 9.30 and 8.23%, respectively. The high compatibility of the low bandgap porphyrin dimers with the wide-bandgap small molecule provides a new threesome with PC₇₁BM for highly efficient panchromatic ternary organic solar cells.

Charge Carrier Polarity Modulation in Diketopyrrolopyrrole-Based Low Band Gap Semiconductors by Terminal Functionalization

Organic semiconductors with variable charge carrier polarity are required for optoelectronic applications. Herein, we report the synthesis of three novel diketopyrrolopyrrole (DPP)-based D-A molecules having three different terminal groups (amide, ester, and dicyano) and study their electronic properties. An increase in electron acceptor strength from amide to dicyano leads to a bathochromic shift in absorption. Photoconductivity and field effect transistor (FET) measurements confirmed that a small increase in acceptor strength can result in a large change in the charge transport properties from p-type to n-type. The molecule with an amide group, DPP-amide, exhibited a moderate p-type mobility (1.3 × 10^-2 cm² V^-1 s^-1), whereas good n-type mobilities were observed for molecules with an ester moiety, DPP-ester (1.5 × 10^-2 cm² V^-1 s^-1), and with a dicyano group, DPP-DCV (1 × 10^-2 cm² V^-1 s^-1). The terminal functional group modification approach presented here is a simple and efficient method to alter the charge carrier polarity of organic semiconductors.

Influence of Branched Alkyl Ester-Labeled Side Chains on Specific Chain Arrangement and Charge-Transport Properties of Diketopyrrolopyrrole-Based Conjugated Polymers

A series of diketopyrrolopyrrole (DPP)-based copolymers, with DPP and bithiophene (BT) as the electron-acceptor and donor backbone units, respectively, are synthesized with branched alkyl side chains that are either directly coupled to the N-positions of DPP or separated by an alkyl ester group. The ester moieties in the side chains induce specific cohesive molecular interactions between these side chains, as compared to the alkyl-only side chains with weak van der Waals interactions. Structure analysis of the DPPBT-based copolymers demonstrated that the introduction of a proper alkyl ester spacer to the branched alkyl chains can shorten the π-π stacking distance between the DPPBT backbones down to 3.61 Å and promote the development of two-dimensionally extended domains. DPPBT-based copolymers, including different branched alkyl ester-labeled side chains, are spun-cast on polymer-treated SiO₂ dielectrics from dilute chloroform solutions for organic thin-film transistors. A DPPBT-based copolymer with properly engineered side chains (i.e., 2-decyltetradecyl ester-labeled side chains) shows the highest hole mobility of 2.30 cm² V^-1 s^-1 and an on/off current ratio of above 10⁶.

A comparative analysis of symmetric diketopyrrolopyrrole-cored small conjugated molecules with aromatic flanks: From geometry to charge transport

Diketopyrrolopyrrole (DPP) derivatives are promising compounds for application in organic electronics. Here, we investigate several symmetrical N-unsubstituted and N-methyl substituted DPPs which differ in the heteroatom in the aromatic flanks. The conformational, electronic, and optical properties are characterized for single molecules in vacuum or a solvent. The intermolecular interactions are evaluated for interacting dimers. Here, a number of stacking geometries is tested, and dimers with mutual orientation of the molecules corresponding to the minimal binding energies are determined. The predicted charge carrier mobilities for stacks having minimal binding energies corroborate experimentally measured values. We conclude that DFT prediction of such stacks is a promising and computationally inexpensive approach to a rough estimation of transport properties. Additionally, the super-cell of the experimentally resolved crystal structure is used to study the dynamics and to compute the charge transport along the hopping pathways. We discuss obtained high mobilities and relate them to the symmetry of DPP core. © 2018 Wiley Periodicals, Inc.

New Diketopyrrolopyrrole-Based Ratiometric Fluorescent Probe for Intracellular Esterase Detection and Discrimination of Live and Dead Cells in Different Fluorescence Channels

A new diketopyrrolopyrrole-based fluorescent probe (DPP-AM) was designed and synthesized for ratiometric detection of esterase and for imaging of live and dead cells in different modes. DPP-AM showed red fluorescence because of the intramolecular charge transfer (ICT) process from the DPP moiety to the pyridinium cation and gave remarkable ratio changes (about 70 folds), with the fluorescence changing from red to yellow, after treating with esterase because of the broken ICT process. Besides, the detection limit of DPP-AM toward esterase in vitro was 9.51 × 10^-5 U/mL. After pretreating with H₂O₂ and ultraviolet light radiation, the health status of TPC1 cells was successfully imaged. More importantly, DPP-AM showed yellow fluorescence in live cells and a red fluorescent signal in dead cells, indicating that DPP-AM has great potential applications for assessing esterase activity as well as for discriminating live and dead cells.

Direct (Hetero)Arylation Polymerization of a Spirobifluorene and a Dithienyl-Diketopyrrolopyrrole Derivative: New Donor Polymers for Organic Solar Cells

The synthesis and preliminary evaluation as donor material for organic photovoltaics of the poly(diketopyrrolopyrrole-spirobifluorene) (PDPPSBF) is reported herein. Prepared via homogeneous and heterogeneous direct (hetero)arylation polymerization (DHAP), through the use of different catalytic systems, conjugated polymers with comparable molecular weights were obtained. The polymers exhibited strong optical absorption out to 700 nm as thin-films and had appropriate electronic energy levels for use as a donor with PC70BM. Bulk heterojunction solar cells were fabricated giving power conversion efficiencies above 4%. These results reveal the potential of such polymers prepared in only three steps from affordable and commercially available starting materials.

Langmuir-Blodgett Thin Films of Diketopyrrolopyrrole-Based Amphiphiles

We report on two π-conjugated donor-acceptor-donor (D-A-D) molecules of amphiphilic nature, aiming to promote intermolecular ordering and carrier mobility in organic electronic devices. Diketopyrrolopyrrole was selected as the acceptor moiety that was disubstituted with nonpolar and polar functional groups, thereby providing the amphiphilic structures. This structural design resulted in materials with a strong intermolecular order in the solid state, which was confirmed by differential scanning calorimetry and polarized optical microscopy. Langmuir-Blodgett (LB) films of ordered mono- and multilayers were transferred onto glass and silicon substrates, with layer quality, coverage, and intermolecular order controlled by layer compression pressure on the LB trough. Organic field-effect transistors and organic photovoltaics devices with active layers consisting of the amphiphilic conjugated D-A-D-type molecules were constructed to demonstrate that the LB technique is an effective layer-by-layer deposition approach to fabricate self-assembled, ordered thin films.

Influences of Conjugation Length on Organic Field-Effect Transistor Performances and Thin Film Structures of Diketopyrrolopyrrole-Oligomers

Here, two diketopyrrolopyrrole (DPP)-based oligomers, DPP-4T and DPP-6T, are studied to reveal the influences of conjugation length on thin-film morphology and organic field-effect transistor (OFET) performances. PDMS-assisted crystallization in a solvent-annealing chamber is applied to prepare crystal arrays of DPP-4T and DPP-6T to optimize the quality of charge channels for OFET characterizations. To deliver insights into microstructure and morphology of thin films, a characterization procedure for determining molecular packing in thin film and crystallinity of the crystal arrays is presented via grazing incidence wide-angle X-ray scattering, electron diffraction, and lattice simulation software package (Cerius2). With the lattice parameters derived from analyses of grazing incidence wide-angle X-ray scattering (GIWAXS) and electron diffraction (ED), the lattice modeling results indicate that the inferior organic field-effect transistor (OFET) performances of DPP-6T are attributed to longer π-stacking distance. Also, less-ordered molecular arrangement and lower continuity of crystalline domains, both of which are revealed from crystallinity results, lead to lower mobility of DPP-6T. In this case, longer conjugated backbones with more conformational degrees of freedom thus cause inherent crystal defects during the crystal growth process, despite the potential to enhance intermolecular π-orbital overlap. Therefore, to achieve better OFET performance, suitable backbone length makes conjugated oligomers give high intermolecular π-orbital overlap and low density of structural disorder, which are the priorities for constructing good charge channel.

Dimeric Porphyrin Small Molecules for Efficient Organic Solar Cells with High Photoelectron Response in the Near-Infrared Region

Small molecules (SMs) with elongated backbones are promising for achieving a higher photovoltaic performance. Herein, a dimeric porphyrin small molecule, ZnP2-DPP, consisting of two porphyrin units linked with an ethynylene as the core and two diketopyrrolopyrrole (DPP) units as the arms is designed and synthesized as an electron donor for solution-processed bulk-heterojunction (BHJ) organic solar cells (OSCs). A significantly enhanced power conversion efficiency of 8.45% with an impressive short-circuit current density (J_sc) up to 19.65 mA cm^-2 is achieved for the BHJ OSCs based on ZnP2-DPP under AM 1.5G irradiation (100 mW cm^-2) compared to that for the OSCs based on the dimeric porphyrin linked with bis-ethynylenes reported previously. Furthermore, the devices show broad photoelectron responses up to 1000 nm with high near-infrared external quantum efficiency up to 66% at 780 nm. This is the first study reporting SM OSCs displaying such a large J_sc of about 20 mA cm^-2 simultaneously with a considerably high and deep photoelectron response of up to 1000 nm.

A Supramolecular Nanocomposite as a Near-Infrared-Transmitting Optical Filter for Security and Forensic Applications

Visibly opaque but near-infrared (NIR)-transparent materials are an essential component for night-vision photography, security imaging, and forensic applications. Herein, the development of a novel supramolecular black dye from a diketopyrrolopyrrole (DPP)-based low-molecular-weight organogelator is described. In the solution state, the monomer of DPP-Amide exhibits a deep green color with a broad absorption in the visible region due to firm intramolecular charge transfer from the donor to the acceptor unit. Interestingly, due to the synergistic effect of H-bonding and π-stacking, DPP-Amide can form a black organogel in toluene with complete spectral coverage from 300 to 800 nm, and transmits beyond 850 nm. In the gel state, complete visible-spectrum coverage is achieved due to the simultaneous formation of both H- and J-type aggregates, which is confirmed via absorption studies. To create a free-standing NIR-transmitting elastomeric black filter, nanoscopic molecular aggregates of DPP-Amide (0.15 wt%) are embedded into a poly(dimethylsiloxane) matrix. This nanocomposite possesses high NIR transparency with good thermal and photostability for practical applications. Finally, the use of the developed material for NIR photography, security, and forensic-related applications is demonstrated.