Solvent effect on the photophysical properties of 4-phenoxy-N-methyl-1,8-naphthalimide

The photophysical properties of N-methyl-1,8-naphthalimide (NI) and 4-phenoxy-N-methyl-1,8-naphthalimide (4-PNI) are studied by steady-state and time-resolved emission measurements. Both absorption and fluorescence spectra are red-shifted when the electron donor phenoxy group (–OPh) is introduced at the C-4 position. Compared to NI, the spectral shift in acetonitrile is 27 and 42 nm for the absorption and fluorescence, respectively. The 4-PNI shows high fluorescence emission in non-polar aprotic solvents that can be ascribed to stabilization of the S1 state. The emission intensity of the 4-PNI decreases by addition of water to dioxane solution, and the fluorescence quenching occurs by combination of dynamic and static contribution ascribed to specific solute–solvent interaction.