Bithiazole: An Intriguing Electron-Deficient Building for Plastic Electronic Applications

Isomers of n-Type Poly(thiophene-alt-co-thiazole) for Organic Thermoelectrics

n-Type polythiophene represents a promising category of n-type polymer thermoelectric materials known for their straightforward structure and scalable synthesis. However, n-type polythiophene often suffers from a twisted backbone and poor stacking property when introducing high-density electron-withdrawing groups for a lower lowest unoccupied molecular orbital (LUMO) level, which is considered to be beneficial for n-doping efficiency. Herein, we developed two isomers of polythiophene derivatives, PTTz1 and PTTz2, by inserting thiazole units into the polythiophene backbone composed of thieno[3,4-c]pyrrole-4,6-dione (TPD) and thiophene-3,4-dicarbonitrile (2CNT). Although PTTz1 and PTTz2 share a similar polymer skeleton, they differ in thiazole configuration, with the nitrogen atoms of the thiazole units oriented toward TPD and 2CNT, respectively. The insertion of thiazole units significantly planarizes the polythiophene backbone while largely preserving low LUMO levels. Notably, PTTz2 exhibits a more coplanar backbone and closer π-stacking compared to PTTz1, resulting in a greatly enhanced electron mobility. Both PTTz1 and PTTz2 can be easily n-doped due to their deep LUMO levels. PTTz2 demonstrates superior thermoelectric performance, with an electrical conductivity of 50.3 S cm-1 and a power factor of 23.8 μW m-1 K-2, which is approximately double that of PTTz1. This study highlights the impact of the thiazole unit on n-type polythiophene derivatives and provides valuable guidelines for the design of high-performance n-type polymer thermoelectric materials.

Effects of donor and acceptor substituents on the photophysics of 4-ethynyl-2,1,3-benzothiadiazole derivatives

The present work explores the photophysical, electrochemical, and fluorescence polarization properties of a group of π-conjugated phenylethynyl-2,1,3-benzothiadiazole derivatives (BTDs) bearing different electron-donating (ED) or electron-withdrawing (EW) substituents at the para position of the phenylethynyl moiety. The BTDs were synthesized through the Sonogashira cross-coupling reaction between 4-bromo-2,1,3-benzothiadiazole and the respective para-substituted phenylethynyl derivatives. The BTDs with the EW-substituents show relatively weak solvatochromic behavior, while the BTDs with the strong ED-substituents like methoxy and N,N-dimethylamino-based substituents (BTDPhOMe and BTDPhNMe2) exhibit a pronounced solvatochromic behavior. The change in dipole moments in the excited states of the derivatives was calculated using Lippert-Mataga plots. The conclusions drawn on the spectral behavior of the molecules could be rationalized by TD-DFT calculations involving electron density difference (EDD) maps that correlate with the ICT characteristics of the molecules. The experimental and theoretical calculations reveal that the BTDs with the strong ED-substituents (strong push-pull type BTDs) have a strong ICT character in the excited state. These strong push-pull type BTDs show high fluorescence quantum yield (ΦF) in apolar solvents and low ΦF in polar solvents. In contrast, the BTDs with the weak ED-substituents (weak push-pull type BTDs) and EW-substituents (pull-pull type BTDs) have a weaker ICT character with low ΦF in apolar and high ΦF in polar solvent media. There is good a agreement among the HOMO-LUMO band gaps obtained from absorption spectroscopy and electrochemical studies and theoretical calculations. The fluorescence anisotropy measurement in the glycerol medium shows that the studied BTDs generally exhibit higher sensitivity towards microviscosity than the traditional DPH fluorescence anisotropy probe.

Synergistic Use of All-Acceptor Strategies for the Preparation of an Organic Semiconductor and the Realization of High Electron Transport Properties in Organic Field-Effect Transistors

The development of n-type organic semiconductor materials for transporting electrons as part of logic circuits is equally important to the development of p-type materials for transporting holes. Currently, progress in research on n-type materials is relatively backward, and the number of polymers with high electron mobility is limited. As the core component of the organic field-effect transistor (OFET), the rational design and judicious selection of the structure of organic semiconductor materials are crucial to enhance the performance of devices. A novel conjugated copolymer with an all-acceptor structure was synthesized based on an effective chemical structure modification and design strategy. PDPPTT-2Tz was obtained by the Stille coupling of the DPPTT monomer with 2Tz-SnMe3, which features high molecular weight and thermal stability. The low-lying lowest unoccupied molecular orbital (LUMO) energy level of the copolymer was attributed to the introduction of electron-deficient bithiazole. DFT calculations revealed that this material is highly planar. The effect of modulation from a donor-acceptor to acceptor-acceptor structure on the improvement of electron mobility was significant, which showed a maximum value of 1.29 cm2 V-1 s-1 and an average value of 0.81 cm2 V-1 s-1 for electron mobility in BGBC-based OFET devices. Our results demonstrate that DPP-based polymers can be used not only as excellent p-type materials but also as promising n-type materials.

Molecular Tuning in Diaryl-Capped Pyrrolo[2,3-d:5,4-d']bisthiazoles: Effects of Terminal Aryl Unit and Comparison to Dithieno[3,2-b:2',3'-d]pyrrole Analogues

A series of six conjugated oligomers consisting of a central pyrrolo[2,3-d:5,4-d']bisthiazole (PBTz) end-capped with either thienyl, furyl, or phenyl groups have been prepared from N-alkyl-and N-aryl-pyrrolo[2,3-d:5,4-d']bisthiazoles via Stille and Negishi cross-coupling. The full oligomeric series was thoroughly investigated via photophysical and electrochemical studies, in parallel with density functional theory (DFT) calculations, in order to correlate the cumulative effects of both aryl end-groups and N-functionalization on the resulting optical and electronic properties. Through comparison with the analogous dithieno[3,2-b:2',3'-d]pyrrole (DTP) materials, the effect of replacing DTP with PBTz on the material HOMO energy and visible light absorption is quantified.

N-Oxide S-O chalcogen bonding in conjugated materials

Non-covalent bonding interactions, such as chalcogen bonding, can have a substantial effect on the electronic and physical properties of conjugated polymers and is largely dependent on the strength of interaction. Functional groups that are traditionally used to instill chalcogen bonding such as alkoxy or fluorine substituents can demand challenging synthetic effort, as well as have drastic effects on the electronics of a π-system. The incorporation of a N-oxide functionality into bithiazole-containing materials, a synthetically simple transformation, has been entirely overlooked until now. A systematic analysis of the effects of N-oxidation on the electronic and physical properties of bithiazole-containing materials has been undertaken. N-Oxidation has been found to affect the electronic band gap through increase of the HOMO and lowering of the LUMO. Furthermore, exceptionally strong intramolecular S-O chalcogen bonding interactions in the bithiazole core contribute to rigidification of the conjugated system. Computational analysis of this system has shown this N-oxide chalcogen bonding interaction to be significantly stronger than other chalcogen bonding interactions commonly exploited in conjugated materials.

Design, synthesis and characterization of fused bithiazole- and dithiophene-based low bandgap thienylenevinylene copolymers

The electron-deficient thiazole moiety has high planarity and effective π–π stacking, which leads to the reduction in the energy levels, exhibiting promising charge carrier mobilities.

Understanding Color Tuning and Reversible Oxidation of Conjugated Azomethines

With the aim of achieving reversible oxidation and color tuning, the effect of the central aromatic on the spectroscopic, electrochemical, and spectrochemical properties of a series of electrochromic azomethine triads was investigated. The absorption of the alkylated thiophene derivatives was blue-shifted relative to their unalkylated counterparts when the central aromatic was either a bi- or terthiophene. It was further found that the alkylated thiophene derivatives had larger Stokes shifts than their unsubstituted counterparts. Theoretical calculations demonstrated that the torsion angles of these alkylated cores with respect to the flanking azomethines were responsible for the spectroscopic effects. While the electrochemical oxidation potential of the triads varied by only 100 mV, the reversibility of their anodic process was contingent on the central aromatic. The absorption of the electrochemically produced state red-shifted between 165 and 280 nm from its corresponding neutral state, leading to perceived color changes between orange and blue. Reversible color changes were chemically mediated with ferric chloride/hydrazine. The absorption of the chemically oxidized state shifted between 155 and 220 nm from the corresponding neutral state, contingent on the central aromatic. The palette of perceived colors that was possible with oxidation included orange, yellow, blue, and gray.

Synthesis, characterization and crystal structures of novel fluorinated di(thiazolyl)benzene derivatives

A series of 11 novel fluorinated and non-fluorinated di(thiazolyl)benzenes have been synthesized via microwave assisted Stille coupling and characterized using X-ray crystallography.

Retracted Article: Facile preparation of bithiazole-based material for inkjet printed light-emitting electrochemical cell

Light-emitting electrochemical cell of bithiazole-based material was fabricated by solution processing rendered high external quantum efficiency over 12.8% and luminance of 1.8 10⁴ cd m⁻².

Light-emitting electrochemical cell of bithiazole-based material was fabricated by solution processing rendered high external quantum efficiency over 12.8% and luminance of 1.8 10⁴ cd m^−2.

Efficient Electron Mobility in an All-Acceptor Napthalenediimide-Bithiazole Polymer Semiconductor with Large Backbone Torsion

An all-acceptor napthalenediimide-bithiazole-based co-polymer, P(NDI2OD-BiTz), was synthesized and characterized for application in thin-film transistors. Density functional theory calculations point to an optimal perpendicular dihedral angle of 90° between acceptor units along isolated polymer chains; yet optimized transistors yield electron mobility of 0.11 cm²/(V s) with the use of a zwitterionic naphthalene diimide interlayer. Grazing incidence X-ray diffraction measurements of annealed films reveal that P(NDI2OD-BiTz) adopts a highly ordered edge-on orientation, exactly opposite to similar bithiophene analogs. This report highlights an NDI and thiazole all-acceptor polymer and demonstrates high electron mobility despite its nonplanar backbone conformation.

Dehydration Polymerization for Poly(hetero)arene Conjugated Polymers

The lack of scalable and sustainable methods to prepare conjugated polymers belies their importance in many enabling technologies. Accessing high-performance poly(hetero)arene conjugated polymers by dehydration has remained an unsolved problem in synthetic chemistry and has historically required transitional-metal coupling reactions. Herein, we report a dehydration method that allows access to conjugated heterocyclic materials. By using the technique, we have prepared a series of small molecules and polymers. The reaction avoids using transition metals, proceeds at room temperature, the only required reactant is a simple base and water is the sole by-product. The dehydration reaction is technically simple and provides a sustainable and straightforward method to prepare conjugated heteroarene motifs.