Solution Processable Pentafluorophenyl End-Capped Dithienothiophene Organic Semiconductors for Hole-Transporting Organic Field Effect Transistors

Two solution-processable organic semiconductors, DFPT-DTTR (1) and DFPbT-DTTR (2), composed of pentafluorophenyl (FP) end-capped 3,5-dialkyl dithienothiophene (DTTR) core with thiophene (T) or bithiophene (bT) as π-bridged spacers are developed and investigated for their optical, electrochemical, microstructural, and electrical properties. With more conjugated bithiophene units, compound 2 exhibits a red-shifted UV–vis absorption band and upshifted HOMO/downshifted LUMO energy levels. According to the density functional theory, compound 2 features a more twisted molecular structure due to the intrinsic non-coplanar blocks in the π-backbones. Compound 1-based organic field effect transistors exhibit efficient hole transport with mobility up to 0.48 cm² V⁻¹ s⁻¹. This is one of the high mobility organic semiconductors exhibiting p-channel characteristics based on solution-processable small molecular FP end-capped fused/oligothiophenes. With large and interconnected crystalline morphologies, decreased π–π stacking distance, and less steric hindrance, compound 1 exhibits two orders of magnitude higher mobility than the more distorted 2, which exhibits lower hole mobility of 1.82 × 10⁻³ cm² V⁻¹ s⁻¹.