Synthesis, characterization and photochromic properties of novel spirooxazines

A series of spirooxazine compounds were synthesized via condensation reaction of 1,3,3-trimethyl-2-methyleneindoline with orthohydroxynitroso aromatic derivatives, then esterification with acyl chlorides. Their structures were confirmed by FTIR, ¹H NMR, ¹³C NMR and elemental analyses. Absorption bands in the visible region were observed in UV-VIS absorption spectra (λ_max: 530-665 nm), which were red-shifted as the polarity of solvent increased. Furthermore, these absorption bands also red-shifted with the increase of the electron-donating ability of the 6′-heterocycle substituent, but were nearly unaffected by 9′-acyloxy. The experimental results of thermal decoloration showed that the thermal relaxation progress of the photomerocyanine followed first order kinetics and the relaxation time was tuned in a broad range from 125-1886 s (at 20 °C) by changing electron-donating power on 6′-heterocycle and 9′-acyloxy, these provided a new design strategy to synthesize photochromic molecules which features different and acceptable relaxation time.