Extensive study of the electron donor 1,1,4,4-tetrathiabutadiene (TTB) and of its charge transfer crystal with TCNQ

Abstract

In the spirit of the renewed interest in mixed stack charge-transfer (CT) crystals, made up by alternating π electron-donor and acceptor molecules, we focus attention on a forgotten donor, 1,1,4,4-tetrathiabutadiene (TTB), synthesized more than 35 years ago. We present a spectroscopic and computational characterization of the neutral TTB, and fully characterize the CT crystal with TCNQ. TTB-TCNQ is a mixed stack crystal, with limited degree of CT (about 0.1), despite TTB electron donating strength is only a little smaller than that of the famous TTF. This finding is explained by the small value of the Madelung energy, that we evaluate by a well tested computational approach.