Spiro-Fused Perylene Diimide Arrays

Non-alternant Benzodifluoranthene Tetraimides from 7,8,9,10-Fluoranthene Diimides: Synthesis, Structure, and Optical-Limiting Properties

A novel tetraimide-functionalized non-alternant π-conjugated system, namely, benzodifluoranthene tetraimides (BDFTI), has been designed and synthesized through highly efficient UV-photocyclization of a vinyl-bridged fluoranthene diimide dimer (i. e., FDI-V). The synthesis of FDI-V starts from a straightforward three-step route to produce novel 7,8,9,10-fluoranthene diimide (FDIs) building-blocks, followed by nearly complete bromination and then Stille-coupling reaction to give the desired dimer. The analysis by X-ray crystallography confirms a near-coplanar geometry for FDIs, while BDFTI shows a U-shaped and distorted backbone configuration proven by theoretical optimizations. The tetraimide BDFTI exhibits several advantages over the FDI cores, including an extended absorption band and a red-shift in photoluminescence spectra. This enhancement can be attributed to the presence of additional electron-deficient imide units, which promotes increased intramolecular charge transfer and improved electron affinity. All the imides show a local aromatic characteristic owing to the incorporation of pentagon rings in the π-frameworks. The fully fused BDFTI exhibits nonlinear optical properties as analyzed by the open-aperture Z-scan technique, demonstrating superior optical-limiting performance compared to vinyl-bridged FDI-V. The versatile UV-photocyclization chemistries provide a pathway for developing complex and unique multiimide-functionalized π-conjugated systems, paving the way for creating high-performance optical-limiting materials.

Spiro-Buckybowls: Synthesis and Selective Transformations Toward Chiral and Nonlinear Optical Polycycles

Integration of spirocycles with buckybowls is a promising strategy to construct three-dimensional (3D) curved π-systems and to endow distinctive physicochemical features arising from buckybowls. Herein, a series of carbon-bridged spiro-type heterosumanenes (spiro-HSEs) were synthesized by combining 9,9'-spirobifluorene and dichalcogenasumanenes (DCSs). It is found that spiro-conjugation plays an important role in the geometric and electronic structures of spiro-HSEs. The bowl depth of DCSs moiety becomes larger in the spiro-HSEs. Owing to the Jahn-Teller (J-T) effect, two DCSs segments of spiro-HSEs have different bowl depths accompanied with the unequal distribution of charge in radical cation state. Taking advantage of the typical reactions of DCSs, selective transformations of spiro-HSEs have been adopted in accordance to the nature of chalcogen atoms (S, Se, Te) to bestow the value-added functionalities. The emissive property is enhanced by converting the thiophene rings of S-doped spiro-HSE into thiophene S,S-dioxides. A chiroptical polycycle could be produced by ring-opening of the edge benzene of Se-doped spiro-HSE. The covalent adduct of Te-doped spiro-HSE with Br2 forms non-centrosymmetric halogen-bonded networks, resulting in the high performance second-order nonlinear optics (NLO).

The Synthesis and Properties of Spirophenanthrene

Motivated by the success of 9,9'-spirobifluorene (SBF) in optoelectronic materials, we synthesized a novel spiro compound, spirophenanthrene (SP). Incorporating a phenanthrene unit as the core, we aimed to leverage the π-conjugation of SPs to surpass the limitations of SBF. Experimental and theoretical studies revealed significant advantages over SBF, including red-shifted wavelengths, tunable LUMO energy levels, and enhanced thermal stability. These advantages suggest the potential of SPs as versatile building blocks for diverse optoelectronic devices.

Doubly Spiro-Conjugated Chiral Carbocycles Exhibiting SOMO-HOMO Inversion in Persistent Radical Cations

Persistent chiral organic open-shell systems have captured growing interest due to their potential applications in organic spintronic and optoelectronic devices. Nevertheless, the integration of configurationally stable chirality into an organic open-shell system continues to pose challenges in molecular design. The π-extended skeleton incorporated in spiro-conjugated carbocycles can provide robust chiroptical properties and a significant stabilization of the excited and ionic radical states. However, this approach has been relatively less explored in the design of persistent organic open-shell systems. We report here the (S,S)-, (R,R)-, and meso-isomers of doubly spiro-conjugated carbocycles featuring flat and rigid carbon-bridged para-phenylenevinylene (CPV) of different conjugation lengths connected by two spiro-carbon centers, which we denote D-spiro-CPV for its quasi-dimeric structure. Our synthetic method based on a double lithiation cyclization approach enables facile production of D-spiro-CPV. D-spiro-CPVs exhibit circularly polarized luminescence (CPL) with high fluorescence quantum yields (ΦFL) resulting in a high CPL brightness of 21 M-1 cm-1 and also exhibit high thermal and photostability. The monoradical cation of D-spiro-CPV absorbing near-infrared light is notably persistent, exhibiting a half-life of 570 h under ambient conditions due to doubly spiro-conjugative stabilization. Theoretical and electrochemical studies indicate the radical cation of D-spiro-CPVs presents a non-Aufbau electron filling, exhibiting inversion of the energy level of the singly occupied molecular orbital (SOMO) and the highest (doubly) occupied molecular orbitals with the SOMO level even below the HOMO-1 level (double SHI effect). Our discoveries provide valuable insights into non-Aufbau molecules and the development of configurationally stable, optically active persistent radicals.

Recent progress and prospects of dimer and multimer acceptors for efficient and stable polymer solar cells

High power conversion efficiency (PCE) and long-term stability are essential prerequisites for the commercialization of polymer solar cells (PSCs). Small-molecule acceptors (SMAs) are core materials that have led to recent, rapid increases in the PCEs of the PSCs. However, a critical limitation of the resulting PSCs is their poor long-term stability. Blend morphology degradation from rapid diffusion of SMAs with low glass transition temperatures (Tgs) is considered the main cause of the poor long-term stability of the PSCs. The recent emergence of oligomerized SMAs (OSMAs), composed of two or more repeating SMA units (i.e., dimerized and trimerized SMAs), has shown great promise in overcoming these challenges. This innovation in material design has enabled OSMA-based PSCs to reach impressive PCEs near 19% and exceptional long-term stability. In this review, we summarize the evolution of OSMAs, including their research background and recent progress in molecular design. In particular, we discuss the mechanisms for high PCE and stability of OSMA-based PSCs and suggest useful design guidelines for high-performance OSMAs. Furthermore, we reflect on the existing hurdles and future directions for OSMA materials towards achieving commercially viable PSCs with high PCEs and operational stabilities.

Efficient Intersystem Crossing in Extended Helical Perylene Diimide Dimers with Chalcogen-Annulation

The properties and formation mechanisms of the triplet state have been widely investigated since they are crucial intermediates in photo functional devices. Specifically, helical PDI dimers, horizontal expanded π-conjugated derivatives of PDI, have shown outstanding performance as electron acceptors in enhancing the performance of photovoltaics. Therefore, the exploration of triplet generation in helical PDI dimers plays a crucial role in understanding the mechanisms and excavating their further application. We make use of Se-annulation to induce intersystem crossing (ISC) in helical PDI dimers and further explore the triplet evolution process systematically as the number of Se atoms increases by transient absorption spectroscopy and the hole-electron analysis method. It shows that the twisted molecular conformation has paved the way for potential ISC in a parent molecule PDI2. The incorporation of Se atoms can result in evident promotion in the efficiency of ISC (ϕTPDI2-2Se = 96.9%) compared to the parent molecule PDI2 (ϕTPDI2 = 26.5%), indicating that chalcogen-annulation is also an efficient strategy in a π-extended system. Our results provide useful insights for understanding the triplet evolution process, which can help broaden the application of the π-extended PDI system into high-performance photovoltaics.

Detection of basic amino acids under highly alkaline conditions using a perylene amine-derived probe

pH plays a crucial part in numerous chemical and physiological processes. In this work, a new perylene diimide derivative that acts as a pH-sensitive dye with Bay Area Carboxylic Acid functionality. The derivative utilizes the outstanding thermal, chemical and photochemical stability found in PDI materials and has remarkable UV-visible absorption and fluorescence emission qualities. Based on these properties, a fluorescent probe (PCA) was synthesised using a perylene tetracarbodiimide (PDI) backbone for the recognition of alkaline pH. In alkaline environments where the pH values are between 10 and 14, the fluorescence intensity significantly decreases, and a blue shift occurs, which is a standard feature of alkaline pH probes. The probe demonstrates exceptional sensing ability within the pH range of 10.00-14.00, with notable stability and reversibility. Encapsulation of the probe in a thin polymer film material enhances the pH sensing capability of the system. New sensor has been developed to detect basic amino acids by utilizing the probes' pH response characteristics. this sensor has also been applied to detect the concentration of arginine.

Polymer Photocatalysts Containing Segregated π-Conjugation Units with Electron-Trap Activity for Efficient Natural-light-driven Bacterial Inactivation

Development of highly efficient and metal-free photocatalysts for bacterial inactivation under natural light is a major challenge in photocatalytic antibiosis. Herein, we developed an acidizing solvent-thermal approach for inserting a non-conjugated ethylenediamine segment into the conjugated planes of 3,4,9,10-perylene tetracarboxylic anhydride to generate a photocatalyst containing segregated π-conjugation units (EDA-PTCDA). Under natural light, EDA-PTCDA achieved 99.9 % inactivation of Escherichia coli and Staphylococcus aureus (60 and 45 min), which is the highest efficiency among all the natural light antibacterial reports. The difference in the surface potential and excited charge density corroborated the possibility of a built-in electron-trap effect of the non-conjugated segments of EDA-PTCDA, thus forming a highly active EDA-PTDA/bacteria interface. In addition, EDA-PTCDA exhibited negligible toxicity and damage to normal tissue cells. This catalyst provides a new opportunity for photocatalytic antibiosis under natural light conditions.

Fusing perylene diimide with helicenes

Incorporating perylene diimide (PDI) units into helicene structures has become a useful strategy for giving access to non-planar electron acceptors as well as a method of creating molecules with unique and intriguing chiroptical properties. This minireview describes this fusion of PDIs with helicenes.

Efficient soluble PTCBI-type non-fullerene acceptor materials for organic solar cells

Single perylene diimide (PDI) used as a non-fullerene acceptor (NFA) in organic solar cells (OSCs) is enticing because of its low cost and excellent stability. To improve the photovoltaic performance, it is vital to narrow the bandgap and regulate the stacking behavior. To address this challenge, we synthesize soluble perylenetetracarboxylic bisbenzimidazole (PTCBI) molecules with a bulky side chain at the bay region, by replacing the widely used "swallow tail" type alkyl chains at the imide position of PDI molecules with a planar benzimidazole structure. Compared with PDI molecules, PTCBI molecules exhibit red-shifted UV-vis absorption spectra with larger extinction coefficient, and one magnitude higher electron mobility. Finally, OSCs based on one soluble PTCBI-type NFA, namely MAS-7, exhibit a champion power conversion efficiency (PCE) of 4.34%, which is significantly higher than that of the corresponding PDI-based OSCs and is the highest PCE of PTCBI-based OSCs reported. These results highlight the potential of soluble PTCBI derivatives as NFAs in OSCs.

Spirobifluorene Mediating the Spin-Spin Coupling of Nitronyl Nitroxide Diradicals

To investigate the mechanism of this spiro conjugation magnetic behavior, we designed and synthesized three diradicals─22'SBF-NN, 44'SBF-NN, and 27SBF-NN. They are bridged by spirobifluorene and nitronyl nitroxide (NN) diradicals as the spin centers. Notably, by SQUID and electron paramagnetic resonance (EPR) zero-field splitting data analyses, the 22'SBF-NN and 27SBF-NN diradicals exhibit intramolecular, distinctly antiferromagnetic (AF) coupling, with 2J_(22'SBF-NN)/k_B = -5.86 K and 2J_(27SBF-NN)/k_B = -24.6 K, respectively. The AF of 22'SBF-NN is opposite to that predicted by the spin density alternation rule based on Hund's rule. Diradical intramolecular conjugation coupling bridged by spiro-carbon conjugation is discussed, in which the 22'SBF-NN is smaller than that of 27SBF-NN, corresponding to the room-temperature EPR characterization. This spiro conjugation is weaker than the traditional planar conjugation and generally leads to a weaker spin-spin coupling in the helical biradical molecule. The EPR spectrum of the 44'SBF-NN diradical shows a deformed nine-line curve, indicating intramolecular exchange coupling. The density functional theory calculation gives a very weak coupling constant of 2J_calc/k_B = 0.06 K, with ferromagnetic (FM) interaction as the proof, which is consistent with the spin-polarized prediction. Further analysis of magnetic susceptibility χ_m and VT-EPR data shows that there is indeed an extremely weak FM interaction in the 44' position diradical. We find the bridge, which is a 44' substituted SBF structure, blocks the conjugation and contains a larger twist in steric hindrance, which also hampers sufficient spin density delocalization, resulting in a much weaker spin coupling interaction. Combined with the analysis of molecular orbital calculation results, the anomalous intramolecular AF coupling mechanism of 22'SBF-NN is further explained.

Perylene Diimide-based Non-fullerene Acceptors With A-D-A'-D-A Architecture For Organic Solar Cells

The vinylene-bridged helical PDI dimer (PDI2) has been an alternative PDI building block for non-fullerene acceptor (NFAs). However, the development of PDI2 derivatives still lag behind, and most of PDI2 derivatives based organic solar cells (OSCs) only achieved a moderate power conversion efficiencies (PCE) of less than 8%. In this contribution, an acceptor-donor-acceptor-donor-acceptor (A-D-A'-D-A) architecture was introduced to facilitate the improvement of photovoltaic properties. Two acceptors named diIDTIC-PDI2 and diFIDTIC-PDI2 were designed and synthesized, in which a PDI2 moiety flanked with two indacenodithiophene (IDT) units was employed as the D-A'-D core and 2-(3-oxo-2,3-dihydro-1H-inden-1-ylidene)malononitrile (IC) or fluorinated IC (IC2F) acted as terminal groups, respectively. The photovoltaic performances of these two acceptors were explored using PM1 as the electron donor. Compared to diIDTIC-PDI2, the fluorinated diFIDTIC-PDI2 based OSCs obtained enhanced photovoltaic performance with the best PCE of 9.77%, a V_OC of 0.957 V, J_SC of 13.58 mA cm^-2 and FF of 75.1%. These results illustrate that engineering terminal groups is a robust strategy of enhancing the efficiency of PDI based acceptors with A-D-A'-D-A architecture.

Molecular Carbon Imides

The creation and development of new forms of nanocarbons have fundamentally transformed the scientific landscape in the past three decades. As new members of the nanocarbon family with accurate size, shape, and edge structure, molecular carbon imides (MCIs) have shown unexpected and unique properties. Particularly, the imide functionalization strategy has endowed these rylene-based molecular carbons with fascinating characteristics involving flexible syntheses, tailor-made structures, diverse properties, excellent processability, and good stability. This Perspective elaborates molecular design evolution to functional landscapes, and illustrative examples are given, including a promising library of multi-size and multi-dimensional MCIs with rigidly conjugated π-architectures, ranging from 1D nanoribbon imides and 2D nanographene imides to cross-dimensional MCIs. Although researchers have achieved substantial progress in using MCIs as functional components for exploration of charge transport, photoelectric conversion, and chiral luminescence performances, they are far from unleashing their full potential. Developing highly efficient and regioselective coupling/ring-closure reactions involving the formation of multiple C-C bonds and the annulation of electron-deficient aromatic units is crucial. Prediction by theory with the help of machine learning and artificial intelligence research along with reliable nanotechnology characterization will give an impetus to the blossom of related fields. Future investigations will also have to advance toward─or even focus on─the emerging potential functions, especially in the fields of chiral electronics and spin electronics, which are expected to open new avenues.

Simplified Synthetic Approach to Tetrabrominated Spiro-Cyclopentadithiophene and the Following Derivation to A-D-A Type Acceptor Molecules for Use in Polymer Solar Cells

4,4'-Spiro-bis[cyclopenta[2,1-b;3,4-b']dithiophene] (SCT) is a versatile building block for constructing three-dimensional (3D) π-conjugated molecules for use in organic electronics. In this paper, we report a more convenient synthetic route to SCT and its derivatives, where a structurally symmetric 3,3'-dibromo-5,5'-bis(trimethylsilyl)-2,2'-bithiophene (2) serves as the precursor for both the synthesis of 4H-cyclopenta[2,1-b:3,4-b']dithiophen-4-one (4) and 4-(5,5'-bis(trimethylsilyl)-2,2'-bithiophen-3-yl)-2,6-bis(trimethylsilyl)-4-hydroxy-cyclopenta[2,1-b;3,4-b']dithiophene (5). The later one is the key intermediate for the final brominated SCT building block. Such a "two birds with one stone" strategy simplifies the synthetic approach to the SCT core. Functionalization on the SCT core with different terminal electron-deficient groups, including 1H-indene-1,3(2H)-dione (ID), 2-(3-oxo-2,3-dihydro-1H-inden-1-ylidene)malononitrile (IC), and 2-(5,6-difluoro-3-oxo-2,3-dihydro-1H-inden-1-ylidene)malononitrile (FIC), was carried out, yielding three spiro-conjugated A-D-A type molecules, SCT-(TID)₄, SCT-(TIC)₄, SCT-(TFIC)₄, respectively. The optical spectroscopy and electrochemical properties of these three compounds were investigated and compared to the corresponding linear oligomers. Results revealed that the IC and TFIC terminated compounds showed low-lying HOMO/LUMO energy levels with reduced optical bandgap, making them more suitable for use in polymer solar cells. A power conversion efficiency of 3.73% was achieved for the SCT-(TFIC)₄ based cell, demonstrating the application perspective of 3D molecules.

Structural symmetry-breaking of perylene diimide acceptor at N-position for enhanced photovoltaic performance

The vinylene-bridged helical perylene diimide dimer (PDI2) and derivatives have received considerable attention for application in nonfullerene organic solar cells (OSCs). Benefit from the large natural dipole moment and the...

Rescuing the solid-state fluorescence of perylene diimide dyes by host–guest isolation

A host molecule with an open and flexible backbone was synthesized and is capable of recognizing various perylene diimide dyes. The host exhibits unique universality in improving the solid-state fluorescence of perylene diimide dyes.

Double π-Extended Helicene Derivatives Containing Pentagonal Rings: Synthesis, Crystal Analyses, and Photophysics

Two novel double π-extended [n]helicene (n = 5, 6) derivatives (7b and 9) including pentagonal rings have been synthesized and characterized. Both of them have three isomers containing two enantiomers (P₆), (M₆), and a diastereoisomer in a meso form (P,M). X-ray single crystal analyses suggest that molecules 7b and 9 exhibit offset packing models of (P₆,P₅)- and (M₆,M₅)-isomers. Optical resolution of the resultant compound 7b was finished, and their chiroptical properties, as well as the DFT calculations, were also examined.

Monocyclic and Dicyclic Dehydro[20]annulenes Integrated with Perylene Diimide

A novel kind of monocyclic and dicyclic dehydro[20]annulenes exhibiting specific sizes and topologies from regioselective unilateral ortho-diethynyl PDI, is developed by Cu-catalyzed Glaser-Hay homo-coupling and cross-coupling. Through the integration of electron-deficient PDI chromophores into the dehydroannulene scaffolding, these macrocycles exhibit intense and characteristic absorption properties and the degenerated LUMO levels. The single-crystal X-ray diffraction analysis unambiguously revealed unique porous supramolecular structures, which display micropore characteristics with surface area of 120.74 m²  g^-1 . A moderate electron mobility of 0.05 cm²  V^-1  s^-1 for chlorine-free dehydro[20]annulene based on micrometer-sized single-crystalline transistors was witnessed. The porous and yet semiconducting features signify the prospects of PDI-integrated dehydroannulenes in organic optoelectronics.

Null Exciton-Coupled Chromophoric Dimer Exhibits Symmetry-Breaking Charge Separation

A comprehensive understanding of the structure-property relationships in multichromophoric architectures has pushed the limits for developing robust photosynthetic mimics and molecular photovoltaics. The elusive phenomenon of null exciton splitting has gathered immense attention in recent years owing to the occurrence in unique chromophoric architectures and consequent emergent properties. Herein, we unveil the hitherto unobserved null exciton coupling assisted highly efficient photoinduced symmetry-breaking charge separation (SB-CS) in a Greek cross (+)-oriented spiro-conjugated perylenediimide dimer (Sp-PDI₂). Quantum chemical calculations have rationalized the infrequent manifestation of null exciton coupling behavior in Sp-PDI₂. Negligible contribution of long-range Coulombic and short-range charge-transfer mediated coupling renders a monomer-like spectroscopic signature for Sp-PDI₂ in toluene. The Greek cross (+)-arranged Sp-PDI₂ possesses a selective hole-transfer coupling, facilitating the ultrafast dissociation of null excitons and evolution of the charge-separated state in polar solvents. Radical cationic and anionic spectroscopic signatures were characterized by employing femtosecond transient absorption spectroscopy. The substantial hole transfer electronic coupling and lower activation energy barrier of Sp-PDI₂ accelerated the charge separation rate. The rate of charge recombination (CR) markedly decelerated due to falling into the inverted region of the Marcus parabola, where the driving force of CR is larger than the total reorganization energy for CR. Hence, the ratio of the rates for SB-CS over CR of Sp-PDI₂ exhibited an unprecedently high value of 2647 in acetonitrile. The current study provides impeccable evidence for the role of selective charge filtering in governing efficient SB-CS and thereby novel insights towards the design of biomimics and advanced functional materials.

Temperature Tuning of Coherent Mixing between States Driving Singlet Fission in a Spiro-Fused Terrylenediimide Dimer

The excited-state dynamics of a spiro-fused terrylene-3,4:11,12-bis(dicarboximide) (TDI) dimer (sTDI2) in toluene and 2-methyltetrahydrofuran (mTHF) were investigated as a function of temperature using femtosecond- and nanosecond-transient absorption spectroscopy, as well as two-dimensional electronic spectroscopy. The spiro conjugation and the corresponding geometry of this compound guarantee a short intermonomer distance along with a partial orbital overlap between the orthogonal TDI π-electron systems, providing electronic coupling between the TDIs. Photoexcitation of sTDI2 in toluene, a low dielectric solvent, at 295 K, results in the ultrafast formation of a state composed of a coherent mixture of singlet 1(S1S0), multiexciton 1(T1T1), and charge-transfer (CT) electronic characters. This mixed species decays to decorrelated triplet states on the nanosecond timescale, completing the process of intramolecular singlet fission (SF) in sTDI2. Upon decreasing the temperature from 295 to 200 K, the contribution of the 1(T1T1) state to the mixed species decreases concurrently with an increase in the CT state character. We attribute this behavior to the variation in the vibrational energy level alignment between the states comprising the mixture due to changes in the temperature and hence the local dielectric environment. In contrast, photoexcitation of sTDI2 in more polar mTHF at 295 K results in the formation of a mixed singlet and CT state before undergoing symmetry-breaking charge separation, owing to the increased stabilization of the CT state in the medium. However, in glassy mTHF at 85 K, photoexcited sTDI2 exhibits discernible multiexciton character, comparable to that observed in toluene at 200 K, which we rationalize by the similarity of the dielectric constants under these two sets of conditions. These observations of mixed states of varying diabatic contributions over the range of experimental conditions show that the temperature and the static dielectric constant can directly control the composition of the electronically mixed excited state of sTDI2 and thus the fate of the SF process.

Giant Rylene Imide-Based Electron Acceptors for Organic Photovoltaics

ConspectusRylene imides are oligo(peri-naphthalene)s bearing one or two six-membered carboxylic imide rings. Their flexible reaction sites and unique photoelectronic properties have afforded active research for applications in photovoltaic devices, light-emitting diodes, and fluorescent sensors. Over the past few decades, synthetic flexibility along with the evolution of molecular design principles for novel aromatic imides has rendered these intriguing dyes considerably valuable, especially for organic photovoltaics (OPVs).During the course of molecular evolution, the most difficult criterion to meet is how to modulate the intra- and intermolecular interactions to alter the aggregation behavior of rylene imides as well as their compatibility with donor materials, with the prerequisite that the appropriate molecular energy level is maintained. In the meantime, our group has focused on the precise synthesis of π-extended rylene imide electron acceptors (RIAs) to rationally alter the molecular chemical and electronic structure, packing arrangement, and photoelectronic properties. These powerful molecular design strategies include the construction of a fully conjugated rigid multichromophoric architecture and successful integration of heteroatoms. Herein, these multichromophoric oligomers are precisely defined as giant rylene imides. Importantly, these strategies provide a vast space for progress in RIAs and present a more comprehensive structure-performance relationship network that can be distinguished from other electron acceptor systems. In particular, the successful acquisition of these fused superhelical architectures provides a meaningful reference for the pluralistic development of OPVs, such as triplet organic solar cells and polarized-light photovoltaic detectors. Meanwhile, the introduction of heteroatoms into the rylene conjugated skeleton provides donor/acceptor interfaces with enhanced electronic interactions and thereby suppresses the polaron-pair binding energy. Nonetheless, much remains to be implemented to broaden the absorption capability of rylene imides as well as to realize full utilization of these meaningful chiral isomers with a wide and strong UV-vis spectroscopic response.In this Account, we provide an overview of our novel approaches toward a supermolecular framework and of the reformed molecular design principle for rylene imide-based electron acceptors since 2012. We begin with a discussion of the rapidly emerging synthesis strategies for giant rylene imides. Then several typical examples with remarkable photovoltaic properties and unique working mechanisms are selected, aimed at providing an in-depth discussion of structure-property-performance relationships. The remaining challenges and newly emerging research information for giant rylene imide-based electron acceptors are further put forward. It is our aspiration that this Account will trigger intensive research interest in these pluralist rylene-based electron acceptors, thereby further accelerating the profound sustainable development of organic solar cells.

Rigidly Fused Spiro-Conjugated π-Systems

Spiro-fused π-systems have gained considerable attention for their application as semiconductors in molecular electronics. Here, a synopsis regarding recent breakthroughs in ladderized spirobifluorenes and indeno-spirobifluorenes, along with further spiro-condensed heteroatomic hydrocarbons with donor-acceptor moieties, is provided. Additionally, an extended range of rigid spirobifluorene polymers and specific doubly linked spiro-systems with partial chiral character is discussed. The diverse applications of the aforementioned structures are thoroughly evaluated.

Chiral cyclic [n]spirobifluorenylenes: carbon nanorings consisting of helically arranged quaterphenyl rods illustrating partial units of woven patterns

Chiral cyclic [n]spirobifluorenylenes consisting of helically arranged quaterphenyl rods, illustrating partial units of woven patterns, were designed and synthesized as a new family of carbon nanorings. The synthesis was accomplished by the Ni(0)-mediated Yamamoto-coupling of chiral spirobifluorene building blocks. The structures of the cyclic 3-, 4-, and 5-mers were determined by X-ray crystallographic analysis. These carbon nanorings exhibited a strong violet colored emission with high quantum yields in solution (95%, 93%, and 94% for 3-, 4-, and 5-mer, respectively). Other spectroscopic properties, including their chiroptical properties, were also investigated. The g-values for circularly polarized luminescence were found to be in the order of 10⁻³. Characteristic spiroconjugation induced by multiple (≧3) bifluorenyl units, for example the even-odd effect of the number of units in the matching of the signs of the orbitals, was also indicated by DFT calculations.

Chiral cyclic [n]spirobifluorenylenes consisting of helically arranged quaterphenyl rods, illustrating partial units of woven patterns, were designed and synthesized as a new family of carbon nanorings.

Fuller-Rylenes: Paving the Way for Promising Acceptors

The hybridization of different acceptors remains a fertile ground awaiting exploration, to fully promote the properties of both components. The concept of this work is to exploit a new form of fuller-rylene hybrids as promising acceptors by integrating planar rylene dye and spherical fullerene for boosting the power conversion efficiency. The synthesis of the fuller-rylenes via a straightforward synthetic strategy by one-pot Pd-catalyzed cyclization can be scaled-up. Specifically, our strategy allows the supplements and enhancement of absorption in the visible region, much wider structural and electronic variations by installing R₁ groups as well as decorating R₂ on the perylene core at will, and good processability without compromising the superior characteristics of fullerene. Thus, bay-decorated fuller-rylene S-Fuller-PMI revealed a ground-breaking efficiency as high as 8.01%, even outperforming [6,6]-phenyl-C₆₁-butyric acid methyl ester (PC₆₁BM) as a parallel comparison (7.09%). Our exploration paves a new way for the design of high-efficiency acceptors, which are promising alternatives to PC₆₁BM in photovoltaic devices.

Development of Perylene-Based Non-Fullerene Acceptors through Bay-Functionalization Strategy

Perylene has had a tremendous impact in the history of material research for the molecular semiconductors. Among numerous derivatives of this polyaromatic hydrocarbon, perylene diimide (PDI) represents a promising class of organic materials envisioned as non-fullerene acceptors (NFAs) for the practical organic photovoltaic (OPV) applications due to their enhanced photo- and thermal stability and remarkably high electron affinity, some of which realize band-like transport properties. The present review guides some of the representative achievements in the development of rationally designed PDI systems, highlighting synthetic methodologies based on bay-functionalization strategies for creating well-designed molecular nanostructures and structure-performance relationship of perylene-based small molecular acceptors (SMAs) for the photovoltaic outcomes.

π-Extension, Selenium Incorporation, and Trimerization: "Three in One" for Efficient Perylene Diimide Oligomer-Based Organic Solar Cells

Perylene diimide (PDI) and the vinylene-bridged helical PDI oligomers are versatile building blocks for constructing nonfullerene acceptors (NFAs). In this contribution, a benzene-cored star-shaped NFA, namely, TPDI2-Se, was designed and synthesized for organic solar cells (OSCs). The NFA with smaller π-conjugated blades, namely, TPDI-Se, was synthesized for comparison. Using the commercially available PTB7-Th as the electron donor, the best power conversion efficiency (PCE) of 3.62% was obtained for TPDI-Se-based OSCs. However, a much higher PCE of 8.59% was achieved for TPDI2-Se-based devices owing to the π-extension in the peripheral panels. Moreover, the photovoltaic performance of TPDI2-Se-based OSCs is also superior to those of the parent NFA TPDI2 (PCE of 7.84%)- and the blade moiety PDI2-Se (PCE of 6.61%)- based ones. Additionally, a remarkable short-circuit current (J_sc) value of 17.21 mA/cm² was obtained for TPDI2-Se-based OSCs, which is among the highest J_sc values reported in PDI-based OSCs. These results argue that the so-called "three in one" molecule design strategy of π-extension, selenium incorporation, and trimerization offers a robust approach to constructing high-performance PDI-based NFAs.

De novo strategy with engineering anti-Kasha/Kasha fluorophores enables reliable ratiometric quantification of biomolecules

Fluorescence-based technologies have revolutionized in vivo monitoring of biomolecules. However, significant technical hurdles in both probe chemistry and complex cellular environments have limited the accuracy of quantifying these biomolecules. Herein, we report a generalizable engineering strategy for dual-emission anti-Kasha-active fluorophores, which combine an integrated fluorescein with chromene (IFC) building block with donor-π-acceptor structural modification. These fluorophores exhibit an invariant near-infrared Kasha emission from the S1 state, while their anti-Kasha emission from the S2 state at around 520 nm can be finely regulated via a spirolactone open/closed switch. We introduce bio-recognition moieties to IFC structures, and demonstrate ratiometric quantification of cysteine and glutathione in living cells and animals, using the ratio (S2/S1) with the S1 emission as a reliable internal reference signal. This de novo strategy of tuning anti-Kasha-active properties expands the in vivo ratiometric quantification toolbox for highly accurate analysis in both basic life science research and clinical applications.

Photovoltaic Performances of Fused Ring Acceptors with Isomerized Ladder-Type Dipyran Cores

We precisely design and synthesize two A-π-D-π-A type dipyran-cored nonfullerene acceptors (NFAs) Ph-DTDP_o-OT and Ph-DTDP_i-OT with oxygen atoms at the outer and inner positions, respectively. 3-Hexyloxythiophene is used as the π-spacer to expand the effective conjugation length of the acceptors. These two NFAs possess similar optical band gaps and energy levels. However, the position of the oxygen atom at the dipyran core can markedly influence the molecular packing and aggregation behavior of the resulted acceptors. Ph-DTDP_o-OT with a strong intermolecular affinity tends to form larger aggregates blending with PBDB-T, leading to a lower photovoltaic performance; Ph-DTDP_i-OT presents good miscibility with PBDB-T and the blend films preferentially adopt a face-on orientation. Ph-DTDP_i-OT-based devices display high and balanced hole and electron mobilities, leading to an optimal power conversion efficiency of 11.38%, which is much higher than those of Ph-DTDP_o-OT-based ones (7.60%). Moreover, Ph-DTDP_i-OT-based devices also exhibit a lower nonradiative recombination voltage loss of 0.268 eV. Our work demonstrates that the π-spacer and chemical structure of the core unit can greatly influence the molecular packing and the morphology of blend films, which are critical to the photovoltaic performance of devices.

Designing a near-infrared circularly polarized luminescent dye by dissymmetric spiro-fusion

A novel spiro-fused terrylene dimer (SDT) was designed and synthesized by a dissymmetric spiro-fusion strategy. The spiro-conjugation effect caused a distinct red-shift and enhancement of the absorption spectrum. Two chiral enantiomers of SDT have been absolutely resolved and identified in combination with theoretical calculations. Circularly polarized luminescence (CPL) measurement revealed its potential as a near-infrared chiral luminescent material.

Perylenediimides as more than just non-fullerene acceptors: versatile components in organic, hybrid and perovskite solar cells

The most recent advances in the incorporation of perylenediimides in photovoltaic devices are highlighted.

Propeller-Shaped Aluminum Complexes with an Azaperylene Core in the Ligands

Tris(8-hydroxyquinoline) aluminum(III) (Alq3) and its derivatives, characterized by a propeller-shaped three-dimensionally π-conjugated structure, have been intensively studied in the few past decades on account of their potential utility in optoelectronic applications. Reported herein are the synthesis and properties of π-extended Alq3 complexes that contain an azaperylene core in each ligand. Intramolecular palladium-catalyzed direct C–H arylations or base-promoted arylations were employed to prepare these large Alq3 analogues. A single-crystal X-ray diffraction analysis of one of the obtained Al complexes revealed a unique three-dimensional packing structure within the crystal, i.e., a honeycomb packing along the ab-plane and columnar π-stacks along the c-axis. An Alq3 analogue with azaperylene-dicarboximide ligands exhibited deep blue color in solution with an intense absorption band that extended to 780 nm (λmax = 634 nm; ε = 58,000 M−1 cm−1).

Triperyleno[3,3,3]propellane triimides: achieving a new generation of quasi-D 3h symmetric nanostructures in organic electronics

Rigid three-dimensional (3D) polycyclic aromatic hydrocarbons (PAHs), in particular 3D nanographenes, have garnered interest due to their potential use in semiconductor applications and as models to study through-bond and through-space electronic interactions. Herein we report the development of a novel 3D-symmetric rylene imide building block, triperyleno[3,3,3]propellane triimides (6), that possesses three perylene monoimide subunits fused on a propellane. This building block shows several promising characteristics, including high solubility, large π-surfaces, electron-accepting capabilities, and a variety of reactive sites. Further, the building block is compatible with different reactions to readily yield quasi-D 3h symmetric nanostructures (9, 11, and 13) of varied chemistries. For the 3D nanostructures we observed red-shift absorption maxima and amplification of the absorption coefficients when compared to the individual subunits, indicating intramolecular electronic coupling among the subunits. In addition, the microplates of 9 exhibit comparable mobilities in different directions in the range of 10-3 cm2 V-1 s-1, despite the rather limited intermolecular overlap of the π-conjugated moieties. These findings demonstrate that these quasi-D 3h symmetric rylene imides have potential as 3D nanostructures for a range of materials applications, including in organic electronic devices.

Synthesis, Regioselective Bromination, and Functionalization of Coronene Tetracarboxydiimide

A new method for the effective synthesis of coronene tetracarboxydiimide (CDI) was developed by utilizing inexpensive and nontoxic potassium vinyltrifluoroborate. Controllable brominations of CDI were accomplished to yield CDI mono-, di-, tri-, and tetra-bromides, which could be used as synthon and functionalized by aromatic nucleophilic substitution and the Sonogashira coupling reaction.

Designing indacenodithiophene based non-fullerene acceptors with a donor-acceptor combined bridge for organic solar cells

Non-fullerene small acceptor molecules have gained significant attention for application in organic solar cells owing to their advantages over fullerene based acceptors. Efforts are continuously being made to design novel acceptors with greater efficiencies. Here, optoelectronic properties of four novel acceptor-donor-acceptor (A-D-A) type small molecules (A1, A2, A3 and A4) were studied for their applications in organic solar cells. These molecules contain an indacenodithiophene central core unit joined to different end capped acceptors through a monofluoro substituted benzothiadiazole (FBT) donor acceptor (DA) bridge. The different end capped acceptor groups are; 2-2(2-ethylidene-5,6-difluoro-3-oxo-2,3-dihydroinden-1-ylidene)malononitrile (A1), 2-2(2-ethylidene-3-oxo-2,3-dihydroinden-1-ylidene)malononitrile (A2), 2-(5-ethylidene-6-oxo-5,6-dihydrocyclopenta-b-thiophene-4-ylidene)malononitrile (A3), and 2-2(2-ethylidene-5,6-dicyano-3-oxo-2,3-dihydroinden-1-ylidene)malononitrile (A4). The calculated optoelectronic properties of the designed molecules were compared with a well-known reference compound R, which was recently synthesized and reported as being an excellent A-D-A type acceptor molecule. All designed molecules showed the appropriate frontier molecular orbital diagram for a charge transfer. A4 shows the highest absorption maximum (λ max) of 858.6 nm (in chloroform solvent), which was attributed to the strong electron withdrawing end-capped acceptor group. Among all of the designed molecules, A3 exhibits the highest open circuit voltages (V oc) which was (1.84 V) with PTB7-Th and (1.76 V) with the P3HT donor polymer. Owing to a lower value of λ e with respect to λ h, the designed molecules demonstrated superior electron mobilities when compared with reference R. Among all of the molecules, A4 shows the highest electron mobility owing to the lower value of λ e compared to R.

Progress in the synthesis of perylene bisimide dyes

Rapid progress in the synthesis of perylene bisimide dyes gave an old scaffold new life.