Synthesis and spectral characteristics of fluorescent dyes based on coumarin fluorophore and hindered amine stabilizer in solution and polymer matrices

The spectral properties of novel bifunctional dyes based on – coumarin and diethylamino-coumarin and piperidine parent amine and N-oxyl and N-alkoxy derivatives were compared in cyclohexane, methanol, diethylene glycol, acetonitrile and chloroform solvents and in polystyrene, poly(methyl methacrylate) and poly(vinyl chloride) polymer matrices. The fluorescence of the derivatives excited at the longest-wavelength band around 295 nm is very low for coumarin-based dyes, whereas the fluorescence of the 7-diethylamino-3-carboxy coumarin dyes excited at 420 nm is as intense as that of anthracene in comparable conditions. Intramolecular quenching on the singlet level, monitored by fluorescence and expressed as the ratio of ΦNH/ΦNO for the parent amine and N-oxyl and ΦNOR/ΦNO for N-alkyloxy and N-oxyl, is more efficient in polymer matrices than in solvents. The spectral properties of 7-diethylamino-3-carboxy coumarin fluorophores depend on the polarity and viscosity of the environment. Highest values of quantum yield ratio were observed for 7-diethylamino-3-carboxy coumarin dyes in polystyrene and poly(vinylchloride). Though the fluorescence intensity is higher in chloroform or in poly(vinyl chloride) matrices, the intramolecular quenching efficiency of a given fluorophore by nitroxide is higher in low polarity media, such as cyclohexane and polystyrene.

Research highlights
► Novel coumarin/piperidine bifunctional dyes were synthetized.
► Their spectral properties were compared in solvents and polymer matrices.
► The fluorescence intensity is highest in chloroform or in poly(vinyl chloride).
► The intramolecular quenching is more efficient in polymer matrices than in solvents.
► The intramolecular quenching efficiency by nitroxide is higher in low polarity media.