Structures and Fluorescence Properties for the Crystals, Powders, and Thin Films of Dithienylhexatrienes: Effects of Positional Isomerism

We investigated the structures and fluorescence properties for the crystals, powders, and thin films of the two positional isomers of dithienylpolyene, (E,E,E)-1,6-di­(3-thienyl)­hexa-1,3,5-triene (3T) and 1,6-di­(2-thienyl)­hexa-1,3,5-triene (2T). A combination of experimental single crystal X-ray and theoretical reduced density gradient (RDG)–atoms-in-molecules (AIM) analysis indicates the importance of CH−π and S–S interactions in 3T and CH−π and S−π interactions in 2T on their structure constructions. Although the molecules are arranged similarly in a herringbone fashion in the crystals, the total intermolecular interactions are considered to be significantly stronger in 3T than in 2T. The X-ray diffraction measurements suggest that the degree of structural order in powders and films is higher in 3T than in 2T. The spectroscopic differences for the crystal, powder, and film samples are larger in 3T. The absorption and fluorescence spectra for the film of 3T are blue- and red-shifted, respectively, from those of the crystal and powder, and the maximum fluorescence yields (0.23–0.27) are observed in powders. In 2T, both the absorption and fluorescence spectra of the film are slightly blue-shifted from those of the crystal and powder, and the fluorescence yields are similarly low (≤0.01) for all solids examined. We also find that the film orientation is substrate-dependent in 3T