Photochemical synthesis of 4H-thieno[3,2-c]chromene and their optical properties

4 - [(2-Iodalyloxy) methyl] thiophene-2-carbaldehyde and 5-iodo-4- (aryloxymethyl)thiophene-2-carbaldehydes were obtained by interaction of phenols with 4-chloromethylthiophene-2-carbaldehyde and its 5-iodosubstituted derivative. These compounds underwent ring closure upon irradiation with UV light (254 nm) to form 4H-thieno[3,2-c]chromene-2-carbaldehyde in high yield. The formation of intermediate radical species was detected by EPR method. Comparative analysis of the ring closure methods showed that the photochemical cyclization of 5-iodo-4-(aryloxymethyl) thiophene-2-carbaldehyde is more rational than the Pd-catalyzed intramolecular arylation. A series of substituted 4H-thieno[3,2-c]chromene-2-carbaldehydes was synthesized by the photochemical cyclization of the corresponding precursors. The photophysical properties of the synthesized compounds were studied. The obtained 4H-thieno[3,2-c]chromene-2-carbaldehydes can be used as covert marking pigments.