Fluorescence Behavior of Bis(cyanostyryl)pyrrole Derivatives Depending on the Substituent Position of Cyano Groups in Solution and in Solid State.

We synthesized a novel fluorophore of distyrylpyrrole derivatives possessing cyano groups at different positions on olefin. Their fluorescence properties in solution and solid state were investigated by photoluminescence quantum yield and lifetime measurements, which provided a radiative decay constant ( kf) and nonradiative decay constant ( knr). The derivative with cyano groups at the inner position of the molecule, inner isomer, shows a high fluorescence quantum yield (Φf = 0.43) in solution, while another derivative with a cyano group at the outer position, outer isomer, hardly shows fluorescence (Φf < 0.01) due to the large nonradiative decay ( knr > 10 ns-1). Upon formation of a single crystal or nanoparticles, these difference were inverted; the quantum yield of the outer and inner isomer was enhanced and diminished, respectively. We explained these differences between in solution and solid state by means of analysis of a single X-ray structure and computation study.