| Autor: |
Peterson BN; Department of Chemistry, The College of William and Mary, Williamsburg, Virginia 23187-8795, United States., Alfieri ME; Department of Chemistry, The College of William and Mary, Williamsburg, Virginia 23187-8795, United States., Hood DJ; Department of Chemistry, The College of William and Mary, Williamsburg, Virginia 23187-8795, United States., Hettwer CD; Department of Chemistry, The College of William and Mary, Williamsburg, Virginia 23187-8795, United States., Costantino DV; Department of Chemistry, The College of William and Mary, Williamsburg, Virginia 23187-8795, United States., Tabor DP; Department of Chemistry, Texas A&M University, College Station, Texas 77843, United States., Kidwell NM; Department of Chemistry, The College of William and Mary, Williamsburg, Virginia 23187-8795, United States. |
| Abstrakt: |
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 H 2 O 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 + 1H 2 O excitation spectrum for the water-migration vibronic bands, supporting H 2 O solvent reorganization upon excitation of the 1PhPy chromophore. Fluorescence measurements with increasing H 2 O % 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. |
