Study of naphthopyran derivatives: structure and photochromic properties in solution and in polymer film

Four naphthopyran derivatives, namely, 3,3-bis(naphthalen-1-yl)-3H-naphtho[2,1-b]pyran, C₃₃H₂₂O, NP1, 3,3-bis([1,1'-biphenyl]-4-yl)-3H-naphtho[2,1-b]pyran, C₃₇H₂₆O, NP2, 3,3-bis(4-phenoxyphenyl)-3H-naphtho[2,1-b]pyran, C₃₇H₂₆O₂, NP3, and 3,3-bis(4-methoxy-2-methylphenyl)-3H-naphtho[2,1-b]pyran, C₂₉H₂₆O₃, NP4, were synthesized and their photochromic properties investigated. NP1-NP4 exhibited good photochromism in different solutions and in poly(methyl methacrylate) (PMMA) film under UV light irradiation. Solvatochromism and the electronic and steric effects of the substituent group on photochromism were analyzed and decolouration curves were found to fit a monoexponential kinetic decay in most cases. Single-crystal X-ray analysis of NP1 and NP2 revealed the structure-property relationships. Good fatigue resistance of NP1, both in solution and in the PMMA film, endows it with potential value for applications.