Solvatofluorochromism of N-[2-(2-hydroxylethylamino)-ethyl]-1,8-naphthalimide in protic solvent

A N-substituted naphthalimide derivative N-[2-(2-hydroxylethylamino)-ethyl]-1,8-naphthalimide (HEAN), which contains potential acceptors for hydrogen bond, was synthesized and fully characterized. The fluorescence and UV/vis behaviors of HEAN in different solvents were investigated, and its Stokes shift value and fluorescence quantum yield (Φf) in each solvent were determined. A remarkable fluorescence enhancement of HEAN in protic–polar solvents but a great quenching effect in apolar, less–polar and aprotic–polar solvents were observed, suggesting the key role of the proticity of solvents. In the protic–polar solvents, the fluorescence intensity and the quantum yield of HEAN increased along with a slight red-shift of the characteristic emission wavelength (λem) with the increase of solvent polarity. Maximum Φf value of 0.453 for HEAN was found in water solvent with a Stokes shift of 4636 cm−1. The inhibition of the photoinduced electron transfer (PET) by the intermolecular hydrogen-bonding interactions between protic solvents and HEAN was proposed to be responsible for its strong fluorescence enhancement. Such solvatofluorochromic property of HEAN may make it as a prospective fluorescent chemosensor to distinguish a protic solvent from aprotic solvents.