Unraveling the Ultrafast Photochemical Dynamics of Nitrobenzene in Aqueous Solution

Nicholas Lau, Deborin Ghosh, Susannah L Bourne-Worster, Rhea Kumar, William Whitaker, Jonas Heitland, Julia Davies, Gabriel Karras, Ian Clark, Gregory M. Greetham, Graham Worth, Andrew J Orr-Ewing, Helen Fielding*

*Corresponding author for this work

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

Abstract

Nitroaromatic compounds are major constituents of the brown carbon aerosol particles in the troposphere that absorb near-ultraviolet (UV) and visible solar radiation and have a profound effect on the Earth’s climate. The primary sources of brown carbon include biomass burning, forest fires and residential burning of biofuels, and an important secondary source is photochemistry in aqueous cloud and fog droplets. Nitrobenzene is the smallest nitroaromatic molecule and a model for the photochemical behaviour of larger nitroaromatic compounds. Despite the obvious importance of its droplet photochemistry to the atmospheric environment, there have not been any detailed studies of the ultrafast photochemical dynamics of nitrobenzene in aqueous solution. Here, we combine femtosecond transient absorption spectroscopy, time-resolved infrared spectroscopy, and quantum chemistry calculations, to investigate the primary steps following the near-UV (λ ≥ 340 nm) photoexcitation of aqueous nitrobenzene. To understand the role of the surrounding water molecules on the photochemical dynamics of nitrobenzene, we compare the results of these investigations with analogous measurements in solutions of methanol, acetonitrile, and cyclohexane. We find that vibrational energy transfer to the aqueous environment quenches internal excitation and therefore, unlike the gas phase, we do not observe any evidence for formation of photoproducts on timescales up to 500 ns. We also find that hydrogen-bonding between nitrobenzene and surrounding water molecules slows the S1/S0 internal conversion process.
Original languageEnglish
Pages (from-to)10407-10417
Number of pages11
JournalJournal of the American Chemical Society
Volume146
Issue number15
Early online date4 Apr 2024
DOIs
Publication statusPublished - 17 Apr 2024

Bibliographical note

Publisher Copyright:
© 2024 The Authors. Published by American Chemical Society

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