Solvent-Mediated Charge Transfer Dynamics of a Model Brown Carbon Aerosol Chromophore: Photophysics of 1-Phenylpyrrole Induced by Water Solvation
Solvent-Mediated Charge Transfer Dynamics of a Model Brown Carbon Aerosol Chromophore: Photophysics of 1-Phenylpyrrole Induced by Water Solvation
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棕色碳气溶胶发色团模型的溶剂介导的电荷转移动力学：水溶剂化诱导的 1-苯基吡咯的光物理学
DOI：
10.1021/acs.jpca.2c00585
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发表时间：
2022
期刊：
影响因子：
--
通讯作者：
Kidwell, Nathanael M.
中科院分区：
文献类型：
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作者：
Peterson, Brianna N.;Alfieri, Megan E.;Hood, David J.;Hettwer, Christian D.;Costantino, Daniel V.;Tabor, Daniel P.;Kidwell, Nathanael M.
氮杂环是一类新发现的气溶胶中重要的光吸收发色团，通常被称为“棕色碳”(BRC)气溶胶。由于它们与太阳光化通量的显著吸收和光谱重叠，这些BRC发色团控制着气溶胶的物理和光学性质。为了模拟BRC发色团周围的局部水溶液溶剂化环境，我们用超音速喷射冷却生成了与水和典型的BRC发色团1-苯基吡咯(1PhPy)的冷分子络合物，并用单构象光谱研究了它们之间的分子间相互作用。在这里，我们利用共振双光子电离(R2PI)和紫外光烧孔(UV HB)双共振谱，从分子水平上了解了水的微溶剂化在1PhPy的光激发下的电荷转移中的作用。量子化学计算和一维离散变量表示模拟揭示了1PhPy在添加和不添加单个水分子的情况下的电荷转移效率。综上所述，我们的结果表明，与水的分子间相互作用引导1PhPy的几何构型采用更扭曲的分子内电荷转移(TICT)构型，从而促进了从吡咯给体到苯环受体的电荷转移。此外，1PhPy周围的水网络报告了电荷转移，使得H2O溶剂在基态主要与吡咯环供体相互作用，而在激发态则优先与苯环受体相互作用。在水迁移振动带的1PhPy+1H2O激发谱中，有很大的Franck-Condon活性，这支持了1PhPy发色团激发后的H2O溶剂重组。随着H2O体积分数的增加，荧光测量证实了我们的气相研究，表明极性水溶剂化环境在激发电子态下稳定了1PhPy的TICT组态，从该组态观察到的发射能量比局部激发组态低。
Nitrogen heterocycles are known to be important light-absorbing chromophores in a newly discovered class of aerosols, commonly referred to as “brown carbon” (BrC) aerosols. Due to their significant absorption and spectral overlap with the solar actinic flux, these BrC chromophores steer the physical and optical properties of aerosols. To model the local aqueous solvation environment surrounding BrC chromophores, we generated cold molecular complexes with water and a prototypical BrC chromophore, 1-phenylpyrrole (1PhPy), using supersonic jet-cooling and explored their intermolecular interactions using single-conformation spectroscopy. Herein, we utilized resonant two-photon ionization (R2PI) and UV holeburning (UV HB) double-resonance spectroscopies to obtain a molecular-level understanding of the role of water microsolvation in charge transfer upon photoexcitation of 1PhPy. Quantum chemical calculations and one-dimensional discrete variable representation simulations revealed insights into the charge transfer efficacy of 1PhPy with and without addition of a single water molecule. Taken together, our results indicate that the intermolecular interactions with water guide the geometry of 1PhPy to adopt a more twisted intramolecular charge transfer (TICT) configuration, thus facilitating charge transfer from the pyrrole donor to the phenyl ring acceptor. Furthermore, the water network surrounding 1PhPy reports on the charge transfer such that the H2O solvent primarily interacts with the pyrrole ring donor in the ground state, whereas it preferentially interacts with the phenyl ring acceptor in the excited state. Large Franck–Condon activity is evident in the 1PhPy + 1H2O excitation spectrum for the water-migration vibronic bands, supporting H2O solvent reorganization upon excitation of the 1PhPy chromophore. Fluorescence measurements with increasing H2O % volume corroborated our gas-phase studies by indicating that a polar water solvation environment stabilizes the TICT configuration of 1PhPy in the excited electronic state, from which emission is observed at a lower energy compared to the locally excited configuration.