Synthesis of B^III Suboxochlorins

As a new core-modified variant of B^III subporphyrins, B^III suboxochlorins were synthesized from B^III <i>meso</i>-2-formylphenylsubporphyrins via addition reaction with mesitylmagnesium bromide, Friedel-Crafts type cyclization effected with BF₃·OEt₂, and oxidation with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) or AgPF₆. The synthesized B^III suboxochlorins are equipped with a fused and conjugated benzocyclohexene unit at the periphery and display broad and blue-shifted Soret bands and red-shifted and vibronic structured Q-bands as compared with the usual B^III triarylsubporphyrins. These B^III suboxochlorins emit fluorescence, showing a peak over 700 nm and a tail reaching 1000 nm with ca. 2.8% quantum yield.