The role of vibronic coupling in the electronic spectroscopy of maleimide: a multi-mode and multi-state quantum dynamics study.

Andreas Lehr,Graham A Worth,Michael A Parkes,Sandra Gómez

doi:10.1039/d0cp04514d

Abstract

The first two excitation bands below 7 eV in the electronic absorption spectrum of maleimide are investigated using a model Hamiltonian including four low-lying singlet excited states within the manifold of 24 vibrational modes. The role of non-adiabatic effects is studied and shines light on both the broad, inter-state coupling-dominated spectral band as well as the fine-structured, not-so-strong coupled band. Calculations have been performed using the Multiconfigurational Time-Dependent Hartree (MCTDH) wavepacket propagation method as well as its multilayer version (ML-MCTDH) using a quadratic vibronic coupling (QVC) Hamiltonian model where parameters are obtained from fitting adiabatic potential energy surfaces computed by ab initio methods. The quantum dynamics calculations provide information on the relaxation dynamics and the vibrational modes involved. Already with a low-order vibronic coupling model and only a few modes being considered, a quantitative agreement with the experimental spectrum is obtained. However, it is found that all modes need to be considered to get a full picture of the photo-excited relaxation dynamics of this molecule.

Highlights

Small heterocyclic organic compounds are ideal test systems for probing theoretical concepts in photochemistry and photophysics in order to reveal and grasp their photoactive features
Maleimide and its N-alkyl derivates have been subject to experimental absorption spectroscopy by Seliskar et al who identified four electronic transitions below 6.5 eV for maleimide in solution, three being allowed singlet excitations increasing in intensity
These results were later confirmed by studies including a (1+1) REMPI experiment and theoretical investigation by ter Steege et al.16 and Climent et al.17 designating four singlet excited states of np* and pp* character: 11B1(np*), 25272 | Phys

Summary

Introduction

Small heterocyclic organic compounds are ideal test systems for probing theoretical concepts in photochemistry and photophysics in order to reveal and grasp their photoactive features This is motivated by a wide array of applications ranging from organic synthesis through drug design to polymer and biomolecular chemistry. Maleimide and its N-alkyl derivates have been subject to experimental absorption spectroscopy by Seliskar et al who identified four electronic transitions below 6.5 eV for maleimide in solution, three being allowed singlet excitations increasing in intensity.13–15 These results were later confirmed by studies including a (1+1) REMPI experiment and theoretical investigation by ter Steege et al. and Climent et al. designating four singlet excited states of np* and pp* character: 11B1(np*), 25272 | Phys.

Objectives

Results

Conclusion