Solvent-dependent photochemical dynamics of a phenoxazine-based photoredox catalyst

Mahima Sneha, Luke Lewis-Borrell, Darya Shchepanovska, Aditi Bhattacherjee, Jasper L Tyler, Andrew J Orr-Ewing

Research output: Contribution to journalArticle (Academic Journal)peer-review

11 Citations (Scopus)
180 Downloads (Pure)


Organic substitutes for ruthenium and iridium complexes are increasingly finding applications in chemical syntheses involving photoredox catalysis. However, the performance of these organic compounds as electron-transfer photocatalysts depends on their accessible photochemical pathways and excited state lifetimes. Here, the UV-induced dynamics of N-phenyl phenoxazine, chosen as a prototypical N-aryl phenoxazine organic photoredox catalyst, are explored in three solvents, N,N-dimethyl formamide, dichloromethane and toluene, using ultrafast transient absorption spectroscopy. Quantum chemistry calculations reveal the locally excited or charge-transfer electronic character of the excited states, and are used to assign the transient electronic and vibrational bands observed. In toluene-d8, complete ground-state recovery is (31 ± 3) % by internal conversion (IC) from the photo-excited state (or from S1 after IC but before complete vibrational relaxation), (13 ± 2) % via direct decay from vibrationally relaxed S1 (most likely radiative decay, with an estimated radiative lifetime of 13 ns) and (56 ± 3) % via the T1 state (with intersystem crossing (ISC) rate coefficient kISC = (3.3 ± 0.2) ± 108 s-1). In dichloromethane, we find evidence for excited state N-phenyl phenoxazine reaction with the solvent. Excited state lifetimes, ISC rates, and ground-state recovery show only modest variation with changes to the solvent environment because of the locally excited character of the S1 and T1 states.
Original languageEnglish
Pages (from-to)1475 - 1494
JournalZeitschrift für Physikalische Chemie
Early online date9 Jun 2020
Publication statusPublished - 27 Aug 2020

Structured keywords

  • BCS and TECS CDTs


  • photochemistry
  • transient absorption spectroscopy
  • ultrafast dynamics
  • organic photocatalyst


Dive into the research topics of 'Solvent-dependent photochemical dynamics of a phenoxazine-based photoredox catalyst'. Together they form a unique fingerprint.

Cite this