Influence of chirality on the aggregation of a new A-n-D-n-A small molecule with a benzodithiophene core: Spectroscopic and morphological investigations

In this paper, the synthesis and characterization of a new alkoxy benzodithiophene-based small molecule bearing two stereocenters and two end-capping acetyl groups (BDTCOR) are reported. The molecule has been obtained in both enantiopure form (S, S) and stereoisomeric mixture. The spectroscopic properties of BDTCOR in solution were compared to computational data revealing that the molecule is a candidate for optoelectronic applications thanks to a broad UV-Vis absorption spectrum and suitable fluorescence properties. The molecule was deposited as a thin film by physical vapor deposition on SiO2 and PMMA substrates revealing a quite different behavior of the enantiopure form vs. the stereoisomeric mixture. In particular, significant differences were found in film morphology suggesting that, contrary to what observed for the stereoisomeric mixture, enantiopure BDTCOR tends to generate supramolecular well-ordered structures. More-over, while electronic circular dichroism spectra of enantiopure BDTCOR casted films do not show significant signals, vapor-deposited films show intense Cotton effect, suggesting a synergic role of chirality and of the deposition technique on the molecular order.