Synthesis and spectroscopic properties of BODIPY-dithienylethene conjugates

Two red fluorescent triads containing photochromic dithienylethene moiety linked to two 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) via acetylene bond, 1a or single bond, 1b were synthesized and characterized. Although no evident absorption and NMR spectra changes were observed upon irradiation with visible light, the absorption and fluorescence spectra of 1a and 1b are remarkably solvent dependent, in contrast to those of the reference BODIPY-thienyl compounds 2a and 2b, which are essentially solvent independent. Fluorescence intensities of 1a and 1b decreased as the solvent polarity increased, and the fluorescence decay showed two exponentials in polar solvents other than n-hexane. DFT calculations have been carried out to elucidate the spectral behavior of investigated compounds.