Organic Semiconductors with Helical Structure Based on Oligothiophene derivatives Exhibiting Chiral Nematic Phase

Abstract

We have synthesized 2-[5-(4-[(S)-2-methylbutoxy]phenyl)-3-methyl]-2″′-propyl-2:5′-2′:5″-2″:5″′-quaterthiophene ( 10 ), a liquid crystalline semiconductor that exhibits a chiral nematic phase, and used the time-of-flight technique to determine its carrier mobility behavior. In the chiral nematic phase, the positive carrier mobility was 2 × 10−4 cm2/Vs at 120°C and the negative carrier mobility was 1 × 10−4 cm2/Vs, both of which we attribute to electronic processes. For the negative carrier, in addition to the fast electronic process, we also observed a slow carrier transport, having mobility on the order of 10−5 cm2/Vs, which we attribute to ionic conduction. Chiral dimers containing binaphthyl group exhibited stable glassy cholesteric phase and cholesteric thin films with selective reflection band in visible light area could be fabricated. They emitted circularly polarized light with dichroic parameter of 1.3 when UV light was illuminated.