Publications by authors named "Emily J Rabe"

To better understand how hydrogen bonding influences the excited-state landscapes of aza-aromatic materials, we studied hydrogen-bonded complexes of 2,5,8-tris (4-methoxyphenyl)-1,3,4,6,7,9,9b-heptaazaphenalene (TAHz), a molecular photocatalyst related to graphitic carbon nitride, with a variety of phenol derivatives (R-PhOH). By varying the electron-withdrawing character of the para-substituent on the phenol, we can modulate the strength of the hydrogen bond. Using time-resolved photoluminescence, we extract a spectral component associated with the R-PhOH-TAHz hydrogen-bonded complex.

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Article Synopsis
  • Trianisole-heptazine (TAHz), a new derivative of heptazine, effectively catalyzes water oxidation to hydroxyl radicals under specific LED light, marking progress in photocatalysis research.
  • The study focuses on how different chemical substituents influence the photocatalytic activity of various heptazine compounds, particularly regarding hydrogen bonding interactions and electron donation/withdrawal effects.
  • Results indicate that the type of substituent affects the reaction dynamics, with TAHz showing promising metastability that could enhance the photocatalyst's longevity through self-healing mechanisms.
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According to Hund's rule, the lowest triplet state (T) is lower in energy than the lowest excited singlet state (S) in closed-shell molecules. The exchange integral lowers the energy of the triplet state and raises the energy of the singlet state of the same orbital character, leading to a positive singlet-triplet energy gap (Δ). Exceptions are known for biradicals and charge-transfer excited states of large molecules in which the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) are spatially separated, resulting in a small exchange integral.

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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.

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