Synthesis and photochromic properties of spiropyrans containing a fused benzopyranone fragment

New spiro compounds of the indole, phthalazine, isobenzofuran, and benzopyran series, containing a fused benzopyranone fragment in the chromene moiety, were synthesized. Indole derivatives were found to exhibit photochromic properties under stationary conditions at 293 K. The thermal stability of merocyanine isomers sharply decreases upon introduction of electron-withdrawing nitro group into the indole fragment and fusion of a benzene ring to the chromene fragment.