Synthesis and Photochromic Properties of Conjugated Naphthopyran Derivatives

Three novel types of naphthopyran derivatives containing alkoxyl and phenyl moieties, 13-butyl −6,11-dimethyl-3,3-diphenyl-3,13-dihydrobenzo[h]indeno[2,1-f]chromen-13-ol (NP), 13-butyl-3,3-bis(6-methoxy-[1,1′-biphenyl]-3-yl)-6,6-dimethyl-3,13-dihydrobenzo[h] indeno[2,1-f]chromen-13-ol (NP1) and 13-butyl-3,3-bis(6-methoxy-4′-naphthalenyl-[1,1′-biphenyl]-3-yl)-6,11-dimenthyl-3,13-dihydrobenz[h]indeno[2,1-f]chromen-13-ol (NP2), were synthesised and characterised. Measurements indicated that they possessed an excellent photochromic response, a rapid thermal bleaching rate and good fatigue resistance. Meanwhile, the UV maximum absorption wavelengths of NP1 (562 nm) and NP2 (597 nm) appeared bathochromically shifted compared with NP (536 nm). The bleaching rate of NP1 was found to be approximately twice that of NP. The results indicated that the UV maximum absorption wavelength and bleaching rate increase with increasing length of the phenyl side chain moieties. In PMMA film, the compounds showed almost the same photochromic properties in the solid state as in dichloromethane solution. The UV absorbance with high-contrast switching in solid film could be beneficial for practical applications.