Bis-tridentate N-Heterocyclic Carbene Ru(II) Complexes are Promising New Agents for Photodynamic Therapy

Raphael T. Ryan, Kimberly C. Stevens, Rosemary Calabro, Sean Parkin, Jumanah Mahmoud, Doo Young Kim, David K. Heidary, Edith C. Glazer, John P. Selegue

Research output: Contribution to journalArticlepeer-review

32 Scopus citations


Ruthenium(II) complexes developed for photodynamic therapy (PDT) are almost exclusively tris-bidentate systems with C2 or D3 symmetry. This is due to the fact that this structural framework commonly produces long-lived excited states, which, in turn, allow for the generation of large amounts of singlet oxygen (1O2) and other reactive oxygen species. Complexes containing tridentate ligands would be advantageous for biological applications as they are generally achiral (D2d or C2v symmetry), which eliminates the possibility of multiple isomers which could exhibit potentially different interactions with chiral biological entities. However, Ru(II) complexes containing tridentate ligands are rarely studied as candidates for photobiological applications, such as PDT, since they almost exclusively exhibit low quantum yields and very short excited-state lifetimes and, thus, are not capable of generating sufficient 1O2 or engaging in electron transfer reactions. Here, we report a proof-of-concept approach to make bis-tridentate Ru(II) complexes useful for PDT applications by altering their photophysical properties through the inclusion of N-heterocyclic carbene (NHC) ligands. Three NHC and two terpyridine ligands were studied to evaluate the effects of structural and photophysical modulations of bis-substituted Ru(II) complexes. The NHC complexes were found to have superior excited-state lifetimes, 1O2 production, and photocytotoxicity. To the best of our knowledge, these complexes are the most potent light-activated bis-tridentate complexes reported.

Original languageEnglish
Pages (from-to)8882-8892
Number of pages11
JournalInorganic Chemistry
Issue number13
StatePublished - Jul 6 2020

Bibliographical note

Funding Information:
We gratefully acknowledge the Kentucky Science and Engineering Foundation (KSEF-4003-RDE-020) and the National Institutes of Health (GM107586) for the support of this research. Crystallographic work was made possible by the National Science Foundation (NSF) MRI program, grants CHE-0319176 and CHE-1625732.

Publisher Copyright:
Copyright © 2020 American Chemical Society.

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Inorganic Chemistry


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