Proton-Coupled Electron Transfer from Water to a Model Heptazine-Based Molecular Photocatalyst

Emily J. Rabe, Kathryn L. Corp, Andrzej L. Sobolewski, Wolfgang Domcke, Cody W. Schlenker

Research output: Contribution to journalArticlepeer-review

56 Scopus citations

Abstract

To gain mechanistic understanding of heptazine-based photochemistry, we synthesized and studied 2,5,8-tris(4-methoxyphenyl)-1,3,4,6,7,9,9b-heptaazaphenalene (TAHz), a model molecular photocatalyst chemically related to carbon nitride. On the basis of time-resolved photoluminescence (TR-PL) spectroscopy, we kinetically reveal a new feature that emerges in aqueous dispersions of TAHz. Using global target analysis, we spectrally and kinetically resolve the new emission feature to be blue shifted from the steady-state luminescence, and observe a fast decay component exhibiting a kinetic isotope effect (KIE) of 2.9 in H2O versus D2O, not observed in the steady-state PL. From ab initio electronic-structure calculations, we attribute this new PL peak to the fluorescence of an upper excited state of mixed nπ∗/ππ∗ character. In water, the KIE suggests the excited state is quenched by proton-coupled electron transfer, liberating hydroxyl radicals that we detect using terephthalic acid. Our findings are consistent with recent theoretical predictions that heptazine-based photocatalysts can participate in proton-coupled electron transfer with H2O.

Original languageEnglish
Pages (from-to)6257-6261
Number of pages5
JournalJournal of Physical Chemistry Letters
Volume9
Issue number21
DOIs
StatePublished - 1 Nov 2018

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