Unveiling Solvation Dynamics of Excited and Ground States via Ultrafast Pump-Dump-Probe Spectroscopy

The conventional ultrafast pump-probe spectroscopy has primarily focused on examining the formation and decay of the excited state intermediates, but it is very difficult to detect those intermediates while the formation is slow and dissipation is much fast because of the limited concentration during the intrinsic photocycle. To address this issue, a multipulse ultrafast pump-dump-probe spectroscopy was employed to generate and probe the short-lived ground state intermediates (GSIs) in an electronic push-pull pyrene derivative (EPP). This particular derivative undergoes planarized intramolecular charge transfer (PICT) in the excited state upon initial femtosecond pulse excitation. After applying the dump pulse once the PICT was formed, the blue-shifted transient absorption GSIs with the ground state dynamics of the structure recovery was directly observed. It is found that GSIs undergo slower reorganization than the PICT formation in the excited state of EPP due to the solvation effect with different dipole moments of ground states and excited states. These findings provide a comprehensive understanding of the full photocycle dynamics of both the ground and excited states, shedding light on the presence of hidden ground state behaviors.