Molecular Packing and Photoluminescence Efficiency in Odd-Membered Oligothiophene S,S-Dioxides

Abstract

The single-crystal X-ray structures of three odd-membered thiophene oligomers bearing one central thienyl-S,S-dioxide moietytrimer, pentamer, and heptamerare reported. Absolute photoluminescence quantum yields in microcrystalline powders are given for all compounds. The solid-state photoluminescence efficiencies of the trimer (45%) and the pentamer (12%) were up to 1 order of magnitude higher than those generally measured in conventional oligothiophenes, while that of the heptamer amounted to only 2%. These results are accounted for in terms of molecular packing characteristics, which, owing to the competing effects of dipolar intermolecular interactions between the sulfonyl groups and intra- and intermolecular C−H···O hydrogen bondings and S···S interactions, change dramatically on changing the oligomer size. While the trimer is highly distorted and crystallizes in a chiral orthorhombic space group with the molecular long axes markedly tilted with respect to one another, the heptamer displays a coplanar ...