Correlation between Solid-State Photophysical Properties and Molecular Packing in a Series of Indane-1,3-dione Containing Butadiene Derivatives

The solid-state photophysical and photochromic properties and the molecular packing in single crystals of a series of donor−acceptor-substituted butadiene derivatives with alkoxy groups as donor and indane-1,3-dione as acceptor are reported. These materials showed significant enhancement and red-shift in fluorescence in the solid state compared to that in solution. The single crystal analysis of these derivatives indicated that these effects could be attributed to both improved intramolecular charge transfer due to planarization of the molecules and to intermolecular exciton coupling between adjacent molecules leading to aggregate fluorescence. The character of the aggregate formed (H- or J-type) and extent of aggregation were strongly dependent on the length of the alkyl substituent, and these differences could be correlated to variations in the molecular packing observed in their single crystals. Some of the derivatives could be super cooled to a metastable glassy state with significantly different optical properties. Transformation from crystalline to a highly stable glassy form could also be induced by light, making these materials useful for recording optical images.