Chalcogenopheno[3,2-b]pyrrole-Containing Donor-Acceptor-Donor Organic Semiconducting Small Molecules for Organic Field-Effect Transistors

Comparative Evaluation of Pyrrole Fused Donor Moieties: 1H-Indole and Pyrrolo[2,3-b] Pyridine in Benzothiadiazole-Based D-A-D Type Conjugated Small Molecules for Organic Field-Effect Transistors

Pyrrolic units have been utilized as building blocks for organic semiconducting small molecules and polymers in the recent past. Even though pyrrole-based materials have shown promising semiconducting properties, they have been challenging due to their lower stability under ambient conditions. In this study, we synthesized two pyrrole-fused moieties: 1H-indole (IN) and pyrrolo[2,3-b] pyridine (PPy), which were then explored for their potential as effective donor moieties in organic semiconducting materials. Each donor block was employed to synthesize two donor-acceptor-donor-type small molecules. Thiophene-flanked benzo[c][1,2,5]thiadiazole was used as an acceptor to generate diethyl 6,6'-(benzo[c][1,2,5]thiadiazole-4,7-diylbis(thiophene-5,2-diyl))bis(1-dodecyl-1H-indole-2-carboxylate (IN-BT2T-IN) and diethyl 6,6'-(benzo[c][1,2,5]thiadiazole-4,7-diylbis(thiophene-5,2-diyl))bis(1-dodecyl-1H-pyrrolo[2,3-b]pyridine-2-carboxylate (PPy-BT2T-PPy) donor-acceptor-donor molecules. These novel donor-acceptor-donor molecules were tested for their hole-transport properties by fabricating and testing organic field-effect transistors (OFETs). Both molecules exhibited moderate hole-transporting properties with maximum hole mobilities of 0.00483 and 0.00381 cm2 V-1 s-1 for IN-BT2T-IN and PPy-BT2T-PPy, measured under annealing conditions. The enhanced hole mobilities measured in the annealed OFET devices were attributed to thermally induced crystallinity, as demonstrated by atomic force microscopy and grazing incidence X-ray diffraction measurements.

Diselenophene-Dithioalkylthiophene Based Quinoidal Small Molecules for Ambipolar Organic Field Effect Transistors

This work presents a series of novel quinoidal organic semiconductors based on diselenophene-dithioalkylthiophene (DSpDST) conjugated cores with various side-chain lengths (-thiohexyl, -thiodecyl, and -thiotetradecyl, designated DSpDSTQ-6, DSpDSTQ-10, and DSpDSTQ-14, respectively). The purpose of this research is to develop solution-processable organic semiconductors using dicyanomethylene end-capped organic small molecules for organic field effect transistors (OFETs) application. The physical, electrochemical, and electrical properties of these new DSpDSTQs are systematically studied, along with their performance in OFETs and thin film morphologies. Additionally, the molecular structures of DSpDSTQ are determined through density functional theory (DFT) calculations and single-crystal X-ray diffraction analysis. The results reveal the presence of intramolecular S (alkyl)···Se (selenophene) interactions, which result in a planar SR-containing DSpDSTQ core, thereby promoting extended π-orbital interactions and efficient charge transport in the OFETs. Moreover, the influence of thioalkyl side chain length on surface morphologies and microstructures is investigated. Remarkably, the compound with the shortest thioalkyl chain, DSpDSTQ-6, demonstrates ambipolar carrier transport with the highest electron and hole mobilities of 0.334 and 0.463 cm2 V-1 s-1 , respectively. These findings highlight the excellence of ambipolar characteristics of solution-processable OFETs based on DSpDSTQs even under ambient conditions.