Structural characteristics and optical properties of a series of solvatochromic fluorescent dyes displaying long-wavelength emission

A series of novel, fluorescent, solvatochromic dyes (KSD-series) carrying a 4-dimethylaminophenyl moiety as π-electron donor and an acetyl moiety as π-electron acceptor, conjugated with a five-membered aromatic monoheterocyclic π-linker, were synthesized. In the cases of dyes having a pyrrole, (KSD-1) furan (KSD-2) and thiophene (KSD-3) heterocycle as π-linker, respectively, the plot of Stokes shifts in different solvents as a function of ET(30) solvent polarity value showed good linear correlation. The fluorescence of KSD-4, a π-conjugation extended derivative of KSD-3, varied from blue (491 nm) in toluene to orange (616 nm) in DMSO; KSD-4C, a carboxyl group modified derivative, displayed longer wavelength emission (619 nm) and larger Stokes shift (229 nm, 9486 cm−1) than conventional dyes in methanol solution.