A compact tetrathiafulvalene-benzothiadiazole dyad and its highly symmetrical charge-transfer salt: Ordered donor π-stacks closely bound to their acceptors

Abstract

A compact and planar donor-acceptor molecule 1 comprising tetrathiafulvalene (TTF) and benzothiadiazole (BTD) units has been synthesised and experimentally characterised by structural, optical, and electrochemical methods. Solution-processed and thermally evaporated thin films of 1 have also been explored as active materials in organic field-effect transistors (OFETs). For these devices, hole field-effect mobilities of μFE=(1. 3±0.5)×10-3 and (2.7±0.4)×10-3 cm2 V s-1 were determined for the solution-processed and thermally evaporated thin films, respectively. An intense intramolecular charge-transfer (ICT) transition at around 495 nm dominates the optical absorption spectrum of the neutral dyad, which also shows a weak emission from its ICT state. The iodine-induced oxidation of 1 leads to a partially oxidised crystalline charge-transfer (CT) salt {(1)2I3}, and eventually also to a fully oxidised compound {1I3} 1/2I2. Single crystals of the former CT compound, exhibiting a highly symmetrical crystal structure, reveal a fairly good room temperature electrical conductivity of the order of 2 S cm-1. The one-dimensional spin system bears compactly bonded BTD acceptors (spatial localisation of the LUMO) along its ridge. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.