Metal bacteriochlorins which act as dual singlet oxygen and superoxide generators

Shunichi Fukuzumi, Kei Ohkubo, Xiang Zheng, Yihui Chen, Ravindra K. Pandey, Riqiang Zhan, Karl M. Kadish

Research output: Contribution to journalArticlepeer-review

59 Scopus citations

Abstract

A series of stable free-base, ZnII and PdII bacteriochlorins containing a fused six- or five-member diketo- or imide ring have been synthesized as good candidates for photodynamic therapy sensitizers, and their electrochemical, photophysical, and photochemical properties were examined. Photoexcitation of the palladium bacteriochlorin affords the triplet excited state without fluorescence emission, resulting in formation of singlet oxygen with a high quantum yield due to the heavy atom effect of palladium. Electrochemical studies revealed that the zinc bacteriochlorin has the smallest HOMO-LUMO gap of the investigated compounds, and this value is significantly lower than the triplet excited-state energy of the compound in benzonitrile. Such a small HOMO-LUMO gap of the zinc bacteriochlorin enables intermolecular photoinduced electron transfer from the triplet excited state to the ground state to produce both the radical cation and the radical anion. The radical anion thus produced can transfer an electron to molecular oxygen to produce superoxide anion which was detected by electron spin resonance. The same photosensitizer can also act as an efficient singlet oxygen generator. Thus, the same zinc bacteriochlorin can function as a sensitizer with a dual role in that it produces both singlet oxygen and superoxide anion in an aprotic solvent (benzonitrile).

Original languageEnglish
Pages (from-to)2738-2746
Number of pages9
JournalJournal of Physical Chemistry B
Volume112
Issue number9
DOIs
StatePublished - 6 Mar 2008

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