Understanding Solvent Effects on Luminescent Properties of a Triple Fluorescent ESIPT Compound and Application for White Light Emission

A triple fluorescent compound, N-salicylidene-3-hydroxy-4-(benzo[d]thiazol-2-yl)phenylamine (SalHBP), was dispersed in solid polymers and was developed as a white-light-emitting source in LED by using it as the first simple single compound with different configurations. The CIE coordinates were at (0.29, 0.35), close to those of pure white light. To explore speciation mechanisms in this single compound white light, SalHBP was dissolved in protic, nonpolar, and moderate polar solvent, respectively. Upon excitation, blue, green, and yellowish green emissions were observed from the three solutions at various temperatures. The conformation of SalHBP at room temperature was described by a Car-Parrinello molecular dynamics simulation. With the aid of hybrid density functional theory at the B3LYP/TZVP and PBE0/TZVP levels, three observed emission bands of SalHBP were assigned from the five most probable excited state conformations that were derived from four ground state conformations. The effect of solvent on the emission of SalHBP was summarized as a possibility for forming intermolecular hydrogen bonds between solvent and SalHBP molecules and competition between intra- and intermolecular hydrogen bonds.