Synthesis and photophysical properties of some novel fluorescent dyes based on naphthalimide derivatives

A series of novel naphthalimide dyes with amino and acetylamino functional groups were synthesized through imidation, reduction and acetylation reactions on 4-nitro-1,8-naphthalic anhydride. The synthesized dyes were characterized by DSC, TLC (Rf values), FTIR, 1HNMR, 13CNMR, UV–visible and Fluorometery. Molar extinction coefficients and wavelength maxima were obtained by examining dye solutions in DMF and THF. The results demonstrated that the synthesized dyes have wavelength maxima ranging from 372 to 433 nm in DMF and 370 to 419 nm in THF and molar extinction coefficients 1.1 × 104–1.9 × 104 l mol−1 cm−1 in DMF and 0.84 × 104–1.4 × 104 l mol−1 cm−1 in THF. The absorption spectra of dyes showed that grafting N-substituted naphthalimides does not affect their color whilst the type of substitutions in C-4 position of naphthalimide very effectively changes the color. The fluorescency of these dyes was evaluated and their Stokes shift values were determined as DMF and THF solutions. The results demonstrated that all dyes had fluorescence properties and Stokes shift values were between 4000 and 6600 cm−1 in DMF and 3880 cm−1 and 6400 cm−1 in THF. Measuring of quantum yields of dyes showed that dyes containing N-ester group had the highest and dyes containing 4-acetylamino group had the lowest quantum yield.