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.