Synthesis of isomeric coumarin-fluorene hybrids by photocyclization and the photophysical features

Abstract We prepared isomeric compounds 2a and 2b having fused skeletons of coumarin and fluorene by photochemical cyclization of olefin 1 . They were successfully separated by chromatography, and characterized by NMR spectroscopic and X-ray crystallographic analyses. The molecular structure of 2a was nonplanar due to the repulsion between the carbonyl group of the coumarin moiety and the methylene group at 9-position on the fluorene skeleton whilst that of 2b was planar. They showed different absorption and fluorescence features in solution whereas their spectral profiles of triplet–triplet absorption and phosphorescence were similar to each other.