Spectroscopic characterisation and photodegradation studies of photochromic spiro[fluorene-9,3′-[3′ H]-naphtho[2,1- b]pyrans

Abstract

Condensation between propargyl alcohol derivatives and appropriate naphthols under acidic catalysis afforded the corresponding spirofluorene-[3′ H]-naphtho[2,1- b]pyrans. Here we report on the synthesis of some new substituted compounds in this series. These molecules are photochromic dyes whose properties have been investigated in toluene solution. Thermal bleaching after exposure to polychromatic light has been monitored by UV-Visible spectrophotometry and modelled in order to determine the rate constant of the ring closure process. Photodegradation studies have also been carried out in toluene solution and confirmed that photo-oxidation processes involving both molecular and singlet oxygen are responsible for the loss of optical density when the dyes are irradiated. For the first time, the identification of some new photo-induced by-products was carried out using GC/MS analysis.