Simulation of Pump-Push Molecular Dynamics in the Heptazine-H2O Complex

TL;DR

This study uses ab initio nonadiabatic trajectory calculations to simulate pump-push molecular dynamics in the heptazine-H2O complex, revealing how femtosecond laser pulses can control proton-coupled electron transfer processes.

Contribution

It introduces a novel simulation approach for pump-push dynamics in hydrogen-bonded complexes, highlighting the potential to selectively trigger PCET reactions.

Findings

Pump pulse causes ultrafast relaxation to S1 state with minor PCET.

Push pulse re-excites S1, increasing PCET probability.

Pump-push technique can resolve individual electron and proton transfer steps.

Abstract

Pump-push-probe spectroscopy was employed for the exploration of charge-separation processes in organic photovoltaic blends as well as for proton-coupled electron-transfer (PCET) reactions in hydrogen-bonded complexes of tri-anisole-heptazine with substituted phenols in organic solvents. In the present work, the electron and proton transfer dynamics driven by a femtosecond pump pulse and a time-delayed femtosecond push pulse has been studied with ab initio on-the-fly nonadiabatic trajectory calculations for the hydrogen-bonded heptazine-H2O complex. While the dynamics following the pump pulse is dominated by ultrafast radiationless energy relaxation to the long-lived lowest singlet excited state (S1) of the heptazine chromophore with only minor PCET reactivity, the re-excitation of the transient S1 population by the push pulse results in a much higher PCET reaction probability. These results illustrate that pump-push excitation has the potential to unravel the individual electron and proton transfer processes of PCET reactions on femtosecond time scales.