Tuning the Intramolecular Charge Transfer Emission from Deep Blue to Green in Ambipolar Systems Based on Dibenzothiophene S,S-Dioxide by Manipulation of Conjugation and Strength of the Electron Donor Units

Donor-Acceptor Copolymers with 9-(2-Ethylhexyl)carbazole or Dibenzothiophene-5,5-dioxide Donor Units and 5,6-Difluorobenzo[c][1,2,5]thiadiazole Acceptor Units for Photonics

Semiconducting polymers, particularly of the third generation, including donor-acceptor (D-A) copolymers, are extensively studied due to their huge potential for photonic and electronic applications. Here, we report on two new D-A copolymers, CP1 and CP2, composed of different electron-donor (D) units: 9-(2-ethylhexyl)carbazole or dibenzothiophene-5,5-dioxide, respectively, and of 4,7-bis(4'-(2-octyldodecyl)thiophen-2'-yl)-5,6-difluorobenzo[c][1,2,5]thiadiazole building block with central 5,6-difluorobenzo[c][1,2,5]thiadiazole electron-acceptor (A) units, which were synthesized by Suzuki coupling in the high-boiling solvent xylene and characterized. The copolymers exhibited very good thermal and oxidation stability. A copolymer CP1 with different molecular weights was prepared in order to facilitate a comparison of CP1 with CP2 of comparable molecular weight and to reveal the relationship between molecular weight and properties. The photophysical, electrochemical, and electroluminescence properties were examined. Intense red photoluminescence (PL) with higher PL efficiencies for CP1 than for CP2 was observed in both solutions and films. Red shifts in the PL thin film spectra compared with the PL solution spectra indicated aggregate formation in the solid state. X-ray diffraction measurements revealed differences in the arrangement of molecules in thin films depending on the molecular weight of the copolymers. Light-emitting devices with efficient red emission and low onset voltages were prepared and characterized.

Molecular Engineering in D-π-A-A-Type Conjugated Microporous Polymers for Boosting Photocatalytic Hydrogen Evolution

Conjugated microporous polymer (CMP) photocatalysts with donor-π-acceptor (D-π-A) or donor-acceptor (D-A) structures have garnered great attention for solar-driven hydrogen generation because of their inherent charge separation nature and high surface area. Herein, we design a series of D-π-A-A-type CMP photocatalysts to uncover the influence of the content of the dibenzo[b,d]thiophene-S-S-dioxide (BTDO) acceptor on the photocatalytic activity. The results demonstrate that the acceptor content in the D-π-A-A-type CMP photocatalysts affects the electronic structure, the availability of reaction sites, and the separation between light-generated electrons and holes, which mainly determine the photocatalytic performance for H₂ release. Benefiting from the synergy of light absorption, hydrophilicity, and active sites, the bare polymer PyT-BTDO-2 with an optimized BTDO content exhibits a high H₂ production rate of 230.06 mmol h^-1 g^-1 under simulated sunlight, manifesting that the strategy of D-π-A-A structural design is efficacious for boosting the photocatalytic performance of CMP photocatalysts.

Conformational Control of [2]Rotaxane by Hydrogen Bond

A series of [2]rotaxanes with various functional groups in the axle component was synthesized by the oxidative dimerization of alkynes, which is mediated by a macrocyclic phenanthroline-Cu complex. The rotaxanes were fully characterized by spectroscopic methods, and the structure of a rotaxane was determined by X-ray crystallographic analysis. The interaction between the ring component and the axle component was studied in detail to understand the conformation of the rotaxanes. The presence of the hydrogen bond between the phenanthroline moiety in the macrocyclic component and the acidic proton in the axle component influenced the conformation of rotaxane.

Bisulfone-Functionalized Organic Polymer Photocatalysts for High-Performance Hydrogen Evolution

Conjugated polymers show great potential in the application of photocatalysis, particularly for the photoreduction reaction of water to generate hydrogen. Molecular structure design is a key part for building a high-performance organic photocatalyst. Herein, two bisulfone-containing conjugated polymer photocatalysts were constructed with 1D or 3D polymer structures, and the effect of polymer geometry on photocatalytic activity was studied. It was found that the linear polymer PySEO-1 exhibited increased photocatalytic performance compared with the 3D polymer network PySEO-2 because the enhanced coplanarity of the polymeric chain in PySEO-1 promoted the photogenerated charge-carrier transmission along the 1D main chain. As a result, an attractive hydrogen generation rate of 9477 μmol h^-1  g^-1 was obtained with PySEO-1 under broadband light irradiation. PySEO-1 also exhibited a high external quantum efficiency of 4.1 % at an incident light wavelength of 400 nm, demonstrating that the bisulfone-containing polymers are attractive as organic photocatalysts for hydrogen production.

Conjugated small organic molecules: synthesis and characterization of 4-arylpyrazole-decorated dibenzothiophenes

4-Arylpyrazole-decorated dibenzothiophenes have been synthesized.

Raposo MM, Martínez-Máñez R, Sancenón F. N,N-Diphenylanilino-heterocyclic aldehyde-based chemosensors for UV-vis/NIR and fluorescence Cu(ii) detection

Cu(ii) coordination with aldehyde-containing probes induced the appearance of NIR bands coupled with remarkable colour changes.

Understanding structure-activity relationships in linear polymer photocatalysts for hydrogen evolution

Conjugated polymers have sparked much interest as photocatalysts for hydrogen production. However, beyond basic considerations such as spectral absorption, the factors that dictate their photocatalytic activity are poorly understood. Here we investigate a series of linear conjugated polymers with external quantum efficiencies for hydrogen production between 0.4 and 11.6%. We monitor the generation of the photoactive species from femtoseconds to seconds after light absorption using transient spectroscopy and correlate their yield with the measured photocatalytic activity. Experiments coupled with modeling suggest that the localization of water around the polymer chain due to the incorporation of sulfone groups into an otherwise hydrophobic backbone is crucial for charge generation. Calculations of solution redox potentials and charge transfer free energies demonstrate that electron transfer from the sacrificial donor becomes thermodynamically favored as a result of the more polar local environment, leading to the production of long-lived electrons in these amphiphilic polymers.

While inorganic semiconductors are well-studied for their solar-to-fuel energy conversion abilities, organic materials receive far less attention. Here, authors prepare linear conjugated polymers as H₂ evolution photocatalysts and rationalize photocatalytic activities with fundamental properties.

Deciphering micro-polarity inside the endoplasmic reticulum using a two-photon active solvatofluorochromic probe

A new class of two-photon active and solvatofluorochromic dyes for the determination of ER polarity is reported. The fluorescent colour spans almost the entire visible spectrum. One of the derivatives is rationally designed for specific ER targeting. Finally, the fluorescence spectral scanning technique has been utilised to determine the micro-polarity inside the ER which is found to be much lower than that of water.

Modulation of Donor-Acceptor Distance in a Series of Carbazole Push-Pull Dyes; A Spectroscopic and Computational Study

A series of eight carbazole-cyanoacrylate based donor-acceptor dyes were studied. Within the series the influence of modifying the thiophene bridge, linking donor and acceptor and a change in the nature of the acceptor, from acid to ester, was explored. In this joint experimental and computational study we have used electronic absorbance and emission spectroscopies, Raman spectroscopy and computational modeling (density functional theory). From these studies it was found that extending the bridge length allowed the lowest energy transition to be systematically red shifted by 0.12 eV, allowing for limited tuning of the absorption of dyes using this structural motif. Using the aforementioned techniques we demonstrate that this transition is charge transfer in nature. Furthermore, the extent of charge transfer between donor and acceptor decreases with increasing bridge length and the bridge plays a smaller role in electronically mixing with the acceptor as it is extended.

Constructing a self-assembling C3-symmetric covalently linked (fused) donor–acceptor-type molecule containing a hexaazatriphenylene core

A C₃-symmetric fused donor–acceptor-type molecule containing a hexaazatriphenylene core, with a tendency to form π-stacked aggregates, has been synthesized and studied.

Synthesis and properties of five ring fused aromatic compounds based on S,S-dioxide benzothiophene

Asymmetrical five ring fused compounds based on S,S-dioxide benzothiophene, BTOF and BTOCz, have wide bandgaps and deep HOMO and LUMO levels.

Scale-up Chemical Synthesis of Thermally-activated Delayed Fluorescence Emitters Based on the Dibenzothiophene-S,S-Dioxide Core

We report a procedure to linearly scale-up the synthesis of 2,8-bis(3,6-di-tert-butyl-9H-carbazol-9-yl)dibenzothiophene-S,S-dioxide (compound 4) and 2,8-bis(10H-phenothiazin-10-yl)dibenzothiophene-S,S-dioxide (compound 5) using Buchwald-Hartwig cross-coupling reaction conditions. In addition, we demonstrate a scaled-up synthesis of all non-commercially available starting materials that are required for the amination cross-coupling reaction. In the present article, we provide the detailed synthetic procedures for all of the described compounds, alongside their spectral characterization. This work shows the possibility to produce organic molecules for optoelectronic applications on a large scale, which facilitates their implementation into real world devices.

Novel Polyamides with 5H-Dibenzo[b,f]azepin-5-yl-Substituted Triphenylamine: Synthesis and Visible-NIR Electrochromic Properties

In this study, a new diamine monomer, namely 4,4′-diamino-4″-(5H-dibenzo[b,f]azepin-5-yl)triphenylamine, was prepared and polymerized with four kinds of dicarboxylic acids via direct polycondensation reaction resulting in a novel series of soluble and electroactive polyamides (PAs). The tough thin films of all PAs could be solution-cast onto an indium-tin oxide (ITO)-coated glass substrate owing to the good solubility in polar organic solvents. Two pairs of obvious redox peaks for these films were observed in cyclic voltammetry (CV) with low onset potentials (E_onset) of 0.37–0.42 V accompanying with remarkable reversible color changes between light yellow and dark blue. A new absorption peak at around 915 nm emerged in near infrared (NIR) spectra; the increasing potential indicated that PAs could be used as a NIR electrochromic material. Moreover, the PAs showed high coloration efficiency (CE; η) in the range of 190–259 cm² C⁻¹.

All-solution-processed fluorene/dibenzothiophene-S,S-dioxide blue co-oligomer light-emitting diodes with an electron transporting PEI/ultrafine-ZnO-nanoparticle bilayer

An all solution-processed blue organic light-emitting diode comprising the emissive fluorene/dibenzothiophene-S,S-dioxide co-oligomer and a poly-ethyleneimine/ultrafine-ZnO-nanoparticle bilayer is proposed for the first time.

Derivatizing Tribenzothiophene-Fused Hexa-peri-hexabenzocoronenes with Tunable Optoelectronic Properties

A series of trisbenzothieno[1,2:7,8:13,14]hexa-peri-hexabenzocoronenes were synthesized and characterized by a combination of NMR, 2D NMR, MALDI-TOF MS, UV/Vis absorption spectroscopy, and 2D-WAXS measurement. By structural modulation like decoration of electro-donating alkoxyl chain, and conversion from an electron-rich thiophene ring into an electron-poor thiophene-S,S-dioxide moiety, the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels of the hexabenzocoronenes derivatives can be effectively tuned which is further verified by the DFT calculations and cyclic voltammetry.

Large-Size Star-Shaped Conjugated (Fused) Triphthalocyaninehexaazatriphenylene

Star-shaped triphthalocyaninehexaazatriphenylene 1 was synthesized via condensation between a new building block 1,2-diaminophthalocyanine and cyclohexanehexaone. Compound 1 represents the largest star-shaped phthalocyanine-fused hexaazatriphenylene reported so far. This largely expanded phthalocyanine shows good solubility and has a strong tendency to aggregate both in solution and on the surface, indicating its potential as an active component in organic electronic devices.

Computational study on thermally activated delayed fluorescence of donor–linker–acceptor network molecules

Using density functional theory we have investigated the structure–property relationships of organic molecules with a donor–linker–acceptor (DLA) framework, which can be used as precursors of OLED materials.

Multiple emissions from indenofluorenedione in solution and polymer films

An indenofluorenedione derivative with D–A–D framework exhibits the dual fluorescent channels, which can be controllably switched in broad visible range by changing environmental polarity, leading to sensitive multi-luminescence including white.

Series of Carbazole-Pyrimidine Conjugates: Syntheses and Electronic, Photophysical, and Electrochemical Properties

A series of carbazole-pyrimidine conjugates 1-17 were synthesized by Pd-catalyzed cross-coupling, oxidation, and nucleophilic aromatic substitution reactions. In 1-17, the carbazole moieties are connected at the 4,6-positions of the pyrimidine ring either directly or via ethynylene or vinylene spacers, and various electron-donating or electron-withdrawing substituents are introduced at the 2-position of the pyrimidine ring. The effects of structural variations on the electronic, photophysical, and electrochemical properties of 1-17 were comprehensively investigated. Compounds 1-17 exhibit intramolecular charge-transfer (ICT) states, which essentially lead to moderate-to-strong fluorescence emission with large Stokes shifts depending on the solvent polarity. These compounds tend to show significant changes in optical and fluorescence properties upon addition of trifluoroacetic acid. The electron-accepting ability of these compounds can be tuned by both substituents on the pyrimidine moiety and spacers. The ethynylene spacer lowers both the HOMO and LUMO levels, while the vinylene spacer elevates the HOMO level and lowers the LUMO level. The X-ray crystal structures of 3, 6, 11, and 14 are also disclosed.

Kinetics of thermal-assisted delayed fluorescence in blue organic emitters with large singlet-triplet energy gap

The kinetics of thermally activated delayed fluorescence (TADF) is investigated in dilute solutions of organic materials with application in blue light-emitting diodes (OLEDs). A method to accurately determine the energy barrier (ΔE(a)) and the rate of reverse intersystem crossing (kRisc) in TADF emitters is developed, and applied to investigate the triplet-harvesting mechanism in blue-emitting materials with large singlet-triplet energy gap (ΔE(ST)). In these materials, triplet-triplet annihilation (TTA) is the dominant mechanism for triplet harvesting; however, above a threshold temperature TADF is able to compete with TTA and give enhanced delayed fluorescence. Evidence is obtained for the interplay between the TTA and the TADF mechanisms in these materials.

Synthesis and optical and electrochemical properties of polycyclic aromatic compounds with S,S-dioxide benzothiophene fused seven rings

Two linearly fused polycyclic aromatic compounds (CzBTO and FBTO) containing the S,S-dioxide benzothiophene unit showed high thermal stability and deep HOMO energy levels. FBTO gave a high photoluminescence quantum yield of 77%.