Synthesis, Characterization and Photochromic Properties of Novel Naphthopyrans with Hydrazone Unit Residue

A series of naphthopyrans with hydrazone unit (8a–8m), were synthesized and characterized by 1H NMR, 13C NMR, IR and HRMS. The photochromic properties were investigated under continuous irradiation, in particular regard to the fatigue resistance and the lifetime of the colored open form in solution and polymers. The results showed that these compounds had both good photochromic properties and high fatigue resistance. Detailed studies showed that representative compound 8d (3,3-di-4-methoxybenzoic acid methylenehydrazino-[3H]-naphtho [2,1-b]pyran) had good photochromic properties in THF solution, in solid state, and in polymers, and exhibited a significant bathochromic shift in the spectra of the open forms compared to known naphthopyrans 9 (3,3-diphenyl-[3H]-naphtho[2,1-b]pyran). On the other hand, the higher melting points of target compounds are promising for the polymer film preparation through hot-melt method.