Molecular Dynamics of Excited State Intramolecular Charge Transfer in Solution by Coherent Nuclear Wave Packets

Abstract

Revealing a proper reaction coordinate in a chemical reaction is the key step towards elucidation of the molecular reaction dynamics. In this report, we investigated the dynamics of intramolecular charge transfer (ICT) of 8‐aminopyrene‐1,3,6‐trisulfonic acid (APTS) occurring in the excited state by time‐resolved fluorescence (TF) and TF spectra. Accurate reaction rates and rate‐dependent nuclear wave packets in the product state allow detailed investigation of the molecular reaction dynamics. The ICT rate is solvent dependent: (34 fs)−1, (87 fs)−1, and (∞)−1 in water, formamide, and dimethylformamide, respectively. By recording spectra of the nuclear wave packets for different reaction rates, chemical species responsible for the emission spectra can be positively identified. The origin of the wave packets can be deduced from the amplitude change of the wave packets at different reaction rates, and the vibrational modes that are associated with the reaction coordinate could be identified. Theoretical calculations of the vibrational reorganization energies reproduce the experimental spectrum of the nuclear wave packets and corroborate the conclusions.

Coherent Vibrational Spectrum via Time-Resolved Fluorescence for Molecular Dynamics and Identification of Emitting Species–Application to Excited-State Intramolecular Proton Transfer

“…The vibrational coherences (NWPs) in the initial photoexcited state can be transferred to a product state in the course of an ultrafast process in molecules, including internal conversion, intersystem crossing, and chemical reactions. The NWPs in both the initial photoexcited state and product can be probed by various time-resolved spectroscopies such as transient absorption (TA), − time-resolved fluorescence (TF), − two-dimensional spectroscopy, − and time-resolved X-ray scattering . TA is widely used to observe NWPs because the required high time-resolution can be readily achieved.…”