TY - JOUR
T1 - Proton-Coupled Electron Transfer from Water to a Model Heptazine-Based Molecular Photocatalyst
AU - Rabe, Emily J.
AU - Corp, Kathryn L.
AU - Sobolewski, Andrzej L.
AU - Domcke, Wolfgang
AU - Schlenker, Cody W.
N1 - Publisher Copyright:
© 2018 American Chemical Society.
PY - 2018/11/1
Y1 - 2018/11/1
N2 - 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.
AB - 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.
UR - http://www.scopus.com/inward/record.url?scp=85055552623&partnerID=8YFLogxK
U2 - 10.1021/acs.jpclett.8b02519
DO - 10.1021/acs.jpclett.8b02519
M3 - Article
C2 - 30265537
AN - SCOPUS:85055552623
SN - 1948-7185
VL - 9
SP - 6257
EP - 6261
JO - Journal of Physical Chemistry Letters
JF - Journal of Physical Chemistry Letters
IS - 21
ER -