Greene Hallam J M, Ghosh Deborin, Sazanovich Igor V, Phelps Ryan, Curchod Basile F E, Orr-Ewing Andrew J
School of Chemistry, University of Bristol, Cantock's Close, Bristol BS8 1TS, U.K.
Central Laser Facility, Research Complex at Harwell, Science and Technology Facilities Council, Rutherford Appleton Laboratory, Harwell Oxford, Didcot, Oxfordshire OX11 0QX, U.K.
J Phys Chem Lett. 2024 Sep 12;15(36):9153-9159. doi: 10.1021/acs.jpclett.4c02154. Epub 2024 Aug 29.
Nitrophenols are atmospheric pollutants found in brown carbon aerosols produced by biomass burning. Absorption of solar radiation by these nitrophenols contributes to atmospheric radiative forcing, but quantifying this climate impact requires better understanding of their photochemical pathways. Here, the photochemistry of near-UV (λ = 350 nm) excited -nitrophenol in aqueous solution is investigated using transient absorption spectroscopy and time-resolved infrared spectroscopy over the fs to μs time scale to characterize the excited states, intermediates, and photoproducts. Interpretation of the transient spectroscopy data is supported by quantum chemical calculations using linear-response time-dependent density functional theory (LR-TDDFT). Our results indicate efficient nonradiative decay via an S(ππ*)/S conical intersection leading to hot ground state -nitrophenol which vibrationally cools in solution. A previously unreported minor pathway involves intersystem crossing near an S(nπ*) minimum, with decay of the resulting triplet -nitrophenol facilitated by deprotonation. These efficient relaxation pathways account for the low quantum yields of photodegradation.
硝基酚是生物质燃烧产生的棕碳气溶胶中存在的大气污染物。这些硝基酚对太阳辐射的吸收会导致大气辐射强迫，但要量化这种气候影响，需要更好地了解它们的光化学途径。在此，利用瞬态吸收光谱和时间分辨红外光谱，在飞秒到微秒的时间尺度上研究了近紫外光（λ = 350 nm）激发的对硝基酚在水溶液中的光化学，以表征激发态、中间体和光产物。使用线性响应含时密度泛函理论（LR-TDDFT）进行的量子化学计算支持了对瞬态光谱数据的解释。我们的结果表明，通过S(ππ*)/S锥形交叉点实现了有效的无辐射衰变，从而产生热基态对硝基酚，其在溶液中振动冷却。一条以前未报道的次要途径涉及在S(nπ*)最小值附近的系间窜越，质子脱除促进了由此产生的三重态对硝基酚的衰变。这些有效的弛豫途径导致了光降解的低量子产率。
