Fluorescence enhancement of covalently linked 1-cyano-1,2-diphenylethene chromophores with naphthalene-1,8-diyl linker units: analysis based on kinetic constants

The fluorescence enhancement effect of covalently fixed fluorescent chromophores has been investigated by means of kinetic analysis of decay rate constants and theoretical calculations. Derivatives of 1-cyano-1,2-diphenylethene dimer have a distorted cyclic structure when both ends are clipped with two naphthalene-1,8-diyl linker units. In contrast to the reference monomer derivative, which exhibits only slight fluorescence in solution (Φf < 0.01, τf < 0.1 ns), the dimer derivative shows high fluorescence quantum yield (Φf = 0.55) and long lifetime (τf = 20.6 ns) in dilute solution owing to suppression of the nonradiative decay process (knr = 0.022 ns(-1)). A V-shaped derivative with a covalent linker on one side showed moderate quantum yield and lifetime (Φf = 0.12, τf = 4.9 ns). According to the wavelength shifts of the absorption/fluorescence bands and theoretical calculations by time-dependent density functional theory (TD-DFT), we propose an H-aggregate-type excimer interaction.