Interference among Multiple Vibronic Modes in Two-Dimensional Electronic Spectroscopy

Camille A Farfan,Daniel B Turner

doi:10.3390/math8020157

Abstract

Vibronic coupling between electronic and vibrational states in molecules plays a critical role in most photo-induced phenomena. Many key details about a molecule’s vibronic coupling are hidden in linear spectroscopic measurements, and therefore nonlinear optical spectroscopy methods such as two-dimensional electronic spectroscopy (2D ES) have become more broadly adopted. A single vibrational mode of a molecule leads to a Franck–Condon progression of peaks in a 2D spectrum. Each peak oscillates as a function of the waiting time, and Fourier transformation can produce a spectral slice known as a ‘beating map’ at the oscillation frequency. The single vibrational mode produces a characteristic peak structure in the beating map. Studies of single modes have limited utility, however, because most molecules have numerous vibrational modes that couple to the electronic transition. Interactions or interference among the modes may lead to complicated peak patterns in each beating map. Here, we use lineshape-function theory to simulate 2D ES arising from a system having multiple vibrational modes. The simulations reveal that the peaks in each beating map are affected by all of the vibrational modes and therefore do not isolate a single mode, which was anticipated.

Highlights

Scientists have several distinct interpretations of the term “vibronic coupling” [1,2]
2D ES studies have used this theoretical approach [32,43,44,45,46]. Despite this large body of literature, the interaction among multiple vibronic modes in 2D ES measurements has been observed [7,12,47,48,49], but not studied in detail. In this contribution, we examine explicitly how multiple vibrational modes influence any given beating map constructed from a sequence of 2D spectra, in a context without the many possible nuclear modes and extensive coupling interactions that often obscure this relationship in laboratory measurements
We aim to model the optical response of a molecular system due to excitation by light, which usually takes the form of laser pulses in the case of 2D ES

Summary

Introduction

Scientists have several distinct interpretations of the term “vibronic coupling” [1,2]. Vibronic coupling leads to the ultrafast modulation of a molecule’s electronic energy gap, Eeg (t). Using these complementary views, researchers have shown that vibronic coupling plays a key role in numerous photophysical, photochemical, and photobiological phenomena. Examples include singlet exciton fission [5,6], oxygenic photosynthesis [7], light-harvesting in biological [8,9,10,11,12] and synthetic [13,14,15] systems, and nonadiabatic transformations [16,17,18,19] These studies have relied upon transient absorption and other four-wave mixing spectroscopy techniques

Objectives

Results

Conclusion