Issue 28, 2025

Surface hopping simulations reveal deactivation pathways of a charge transfer system with planarizing and twisting motion

Abstract

Nonadiabatic surface hopping simulations are used to investigate the relaxation pathways after photoexcitation of 4-(indol-1-ylamino)benzonitrile, a prototypical example of N-aryl-substituted 1-aminoindoles. This molecule combines functional groups that can undergo in the excited state twisted as well as planarized intramolecular charge transfer and are potential building blocks for molecular motors. The results of the nonadiabatic dynamics simulation show that after excitation with light in the range of 4.2–4.8 eV, the N-aryl-substituted 1-aminoindole decays rapidly from S3 and S2 into the S1 state. On the S1 potential energy surface, the system relaxes then to one of the charge-transfer minima with twisted amino-phenyl and planarized amino-indole torsional angles. The twist and the planarization occur nearly synchronously, with a slight advance of the twist. The geometric relaxation is accompanied by a change of the electronic structure from a ππ* excitation localized on indole to a charge transfer excitation from the indole and amino groups into the benzonitrile moiety. The simulated time-resolved fluorescence spectrum exhibits a bright band from a locally excited state and a weaker charge-transfer band. The transition energies suggest that the experimentally observed emission happens from the S1 minima. After transition to the ground state, half of the trajectories relax back to the original minimum and half of the trajectories to its enantiomer. The twist and planarization occur nearly synchronously, with planarization slightly leading. The combination of preference to rotate over twisted intermediate structure in the excited state and over more twisted structures in the ground state indicates that some kinetic work is done during a full cycle. Even though the kinetic work done per cycle is small, this might be increased by e.g. introducing substituents.

Graphical abstract: Surface hopping simulations reveal deactivation pathways of a charge transfer system with planarizing and twisting motion

Supplementary files

Article information

Article type
Paper
Submitted
06 Mar 2025
Accepted
19 Jun 2025
First published
02 Jul 2025
This article is Open Access
Creative Commons BY license

Phys. Chem. Chem. Phys., 2025,27, 14985-14998

Surface hopping simulations reveal deactivation pathways of a charge transfer system with planarizing and twisting motion

J. Haberhauer, S. Mai, L. González and C. Hättig, Phys. Chem. Chem. Phys., 2025, 27, 14985 DOI: 10.1039/D5CP00889A

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