Molecular electronic tuning of photosensitizers to enhance photodynamic therapy: Synthetic dicyanobacteriochlorins as a case study

Eunkyung Yang, James R. Diers, Ying Ying Huang, Michael R. Hamblin, Jonathan S. Lindsey, David F. Bocian, Dewey Holten

Research output: Contribution to journalArticlepeer-review

50 Citations (Scopus)

Abstract

Photophysical, photostability, electrochemical and molecular-orbital characteristics are analyzed for a set of stable dicyanobacteriochlorins that are promising photosensitizers for photodynamic therapy (PDT). The bacteriochlorins are the parent compound (BC), dicyano derivative (NC) 2BC and corresponding zinc (NC)2BC-Zn and palladium chelate (NC)2BC-Pd. The order of PDT activity against HeLa human cancer cells in vitro is (NC)2BC-Pd > (NC)2BC > (NC)2BC-Zn ≈ BC. The near-infrared absorption feature of each dicyanobacteriochlorin is bathochromically shifted 35-50 nm (748-763 nm) from that for BC (713 nm). Intersystem crossing to the PDT-active triplet excited state is essentially quantitative for (NC)2BC-Pd. Phosphorescence from (NC)2BC-Pd occurs at 1122 nm (1.1 eV). This value and the measured ground-state redox potentials fix the triplet excited-state redox properties, which underpin PDT activity via Type-1 (electron transfer) pathways. A perhaps counterintuitive (but readily explicable) result is that of the three dicyanobacteriochlorins, the photosensitizer with the shortest triplet lifetime (7 μs), (NC)2BC-Pd has the highest activity. Photostabilities of the dicyanobacteriochlorins and other bacteriochlorins studied recently are investigated and discussed in terms of four phenomena: aggregation, reduction, oxidation and chemical reaction. Collectively, the results and analysis provide fundamental insights concerning the molecular design of PDT agents.

Original languageEnglish
Pages (from-to)605-618
Number of pages14
JournalPhotochemistry and Photobiology
Volume89
Issue number3
DOIs
Publication statusPublished - May 2013
Externally publishedYes

ASJC Scopus subject areas

  • Biochemistry
  • Physical and Theoretical Chemistry

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