PIFA-promoted intramolecular oxidative cyclization of pyrrolo- and indolo[1,2-a]quinoxalino-appended porphyrins: an efficient synthesis of meso,beta-pyrrolo- and indolo[1,2-a]quinoxalino-fused porphyrins

We have developed an efficient protocol for the synthesis of meso,beta-pyrrolo- and indolo[1,2-a]quinoxalino-fused porphyrin systems 7-9 by PIFA-promoted intramolecular oxidative cyclization of easily accessible meso-pyrrolo- and indolo[1,2-a]quinoxalino-appended porphyrins 6a-j. The absorption spectra of meso,beta-pyrrolo- and indolo[1,2-a]quinoxalino-fused porphyrins 7-9 displayed bathochromic shifted (100-150 nm) and broadened Soret bands and Q bands in addition to intense band near IR region. The indolo[1,2-a]quinoxalino-fused porphyrin 9bZn with lower fluorescence quantum yield (0.003) and reduced energy gap (similar to 1.3 eV) was found to sensitize singlet oxygen effectively.