| Novel fluorescent photochromic compounds have been synthesized and tested. The new materials were obtained by covalently linking photochromic dithienylethene moieties to fluorescent 4,4-difluoro-8-(4'-iodophenyl)-1,3,5,7-tetramethyl-4-bora-3a,4a-diaza-s-indacene (BODIPY dye) via a phenylacetylene linker. Photochromic dithienylethenes may exist in two forms, open- and closed-ring isomers. Closed-ring isomers are produced by UV light irradiation of open-ring isomers, and this process is reversed by irradiation with visible light. The new open-ring isomers are highly emissive, whereas the fluorescence is quenched considerably in the closed-ring isomers. The processes of quenching and recovery of fluorescence can be repeated many times without significant loss of its intensity.;In the new compounds, the emission, originating from the dye, appears around 520 nm. When closed-ring isomers are produced, new broad absorption bands arise in the region of 550--600 nm. The new bands overlap with the emission of the BODIPY moiety, so that the observed fluorescence quenching can be accounted for by intramolecular energy transfer.;The switching of fluorescence was investigated in hexane solution and in poly(methyl methacrylate) film. Changes in the properties accompanying such photochromic reactions were detected by means of UV spectroscopy and steady-state fluorescence emission measurements. The photoconversion from open- to closed-ring isomers was determined using NMR spectroscopy. Fatigue resistance was studied by multiple irradiations with UV and visible light. Rates and mechanism of isomerization were established by conducting time-resolved femtosecond experiments. |
