Isomer-Free Quinoidal Building Block Employing 3,4-Phenylenedioxythiophene Unit with Mesomeric Effect for Low-Bandgap Quinoidal Conjugated Polymers

Quinoidal compounds have attractive features as organic semiconducting materials owing to their distinct properties compared to aromatic compounds. The suppression of geometrical isomers is a challenge in the development of quinoid-type molecules. In this study, a novel quinoidal building block, bQuPheDOT-Br, was synthesized by incorporating 3,4-phenylenedioxythiophene (PheDOT). Using the conformation-locking strategy, bQuPheDOT-Br exists as a single isomeric compound with a planar molecular structure, resulting in effective π-electron delocalization. Two quinoidal conjugated polymers, PbQPheDOT-T2 and PbQPheDOT-2FT2, were synthesized. Owing to the planar geometry and possible electron delocalization due to the phenyl ring incorporation of the bQPheDOT unit, PbQPheDOT-T2 and PbQPheDOT-2FT2 exhibited a low bandgap (∼1.3 eV) and near-infrared (NIR) light absorption up to 1200 nm wavelength due to the mesomeric effect. Grazing-incidence wide-angle X-ray scattering revealed that both polymers exhibited high crystallinity up to the fourth order of the (h00) diffraction peaks after thermal annealing, owing to their rigid and planar quinoidal backbone. Finally, the charge transport properties of PbQPheDOT-T2 and PbQPheDOT-2FT2 were evaluated by fabricating organic field-effect transistors as active layers with hole mobilities of 5.2 × 10–2 and 2.6 × 10–2 cm2/Vs, respectively, and electron mobility of 1.0 × 10–2 cm2/Vs for PbQPheDOT-T2

Enhanced N‑type Semiconducting Performance of Asymmetric Monochlorinated Isoindigo-based Semiregioregular Polymers under Dynamic Forces

The asymmetric monochlorination strategy not only effectively addresses the steric issues in conventional dichlorination but also enables the development of promising acceptor units and semiregioregular polymers. Herein, monochlorinated isoindigo (1CIID) is successfully designed and synthesized by selectively introducing single chlorine (Cl) atoms. Furthermore, the 1CIID copolymerizes with two donor counterparts, centrosymmetric 2,2′-bithiophene (2T) and axisymmetric 4,7-di(thiophen-2-yl)benzo[1,2,5]thiadiazole (DTBT), forming two polymers, P1CIID-2T and P1CIID-DTBT. These polymers exhibit notable differences in backbone linearity and dipole moments, influenced by the symmetry of their donor counterparts. In particular, P1CIID-2T, which contains a centrosymmetric 2T unit, demonstrates a linear backbone and a significant dipole moment of 10.20 D. These properties contribute to the favorable film morphology of P1CIID-2T, characterized by highly ordered crystallinity in the presence of fifth-order (500) X-ray diffraction peaks. Notably, P1CIID-2T exhibits a significant improvement in molecular alignment under dynamic force, resulting in over 8-fold improvement in the performance of organic field-effect transistor (OFET) devices, with superior electron mobility up to 1.22 cm2 V−1 s−1. This study represents the first synthesis of asymmetric monochlorinated isoindigo-based conjugated polymers, highlighting the potential of asymmetric monochlorination for developing n-type semiconducting polymers. Moreover, our findings provide valuable insights into the relationship between the molecular structure and properties

Unsymmetrical Small Molecules for Broad-Band Photoresponse and Efficient Charge Transport in Organic Phototransistors

Organic photosensitizers have been investigated as effective light-sensing elements that can promote strong absorption with high field-effect mobility in organic phototransistors (OPTs). In this study, a novel organic photosensitizer is synthesized to demonstrate broad-band photoresponse with enhanced electrical performance. An unsymmetrical small molecule of a solubilizing donor (D-sol)-acceptor (A)-dye donor (D-dye) type connected with a twisted conjugation system is designed for broad-band detection (ranging from 250 to 700 nm). This molecule has high solubility, thereby facilitating the formation of uniformly dispersed nanoparticles in an insulating polymer matrix, which is deposited on top of OPT semiconductors by a simple solution process. The broad-band photodetection shown by the organic photosensitizer is realized with improved mobility close to an order of magnitude and high on/off current ratio (similar to 10(5)) of the organic semiconductor. Furthermore, p-type charge transport behavior in the channel of the OPT is enhanced through the intrinsic electron-accepting ability of the organic photosensitizer caused by the unique molecular configuration. These structural properties of organic photosensitizers contribute to an improvement in broad-band photosensing systems with new optoelectronic properties and functionalities