# Ab Initio Investigation of Intramolecular Charge Transfer States in DMABN by Calculation of Excited State X-ray Absorption Spectra

## TL;DR

This study uses advanced quantum chemical calculations to explore the excited state structures of DMABN and predicts X-ray absorption spectral features that could help experimentally identify intramolecular charge transfer states.

## Contribution

It provides a detailed computational analysis of ICT states in DMABN using EOM-CCSD and TDDFT, and predicts spectral signatures for experimental detection.

## Key findings

- Identified key spectral features associated with ICT states.
- Mapped potential energy surfaces of excited states across conformations.
- Predicted X-ray absorption spectra for future experimental validation.

## Abstract

Dual fluorescence in 4-(dimethylamino)benzonitrile (DMABN) and its derivatives in polar solvents has been studied extensively for the past several decades. An intramolecular charge transfer (ICT) minimum on the excited state potential energy surface, in addition to the localized low-energy (LE) minimum, has been proposed as a mechanism for this dual fluorescence, with large geometric relaxation and molecular orbital reorganization a key feature of the ICT pathway. Herein, we have used both equation-of-motion coupled-cluster with single and double excitations (EOM-CCSD) and time-dependent density functional (TDDFT) methods to investigate the landscape of excited state potential energy surfaces across a number of geometric conformations proposed as ICT structures. In order to correlate these geometries and valence excited states in terms of potential experimental observables, we have calculated the nitrogen K-edge ground and excited state absorption spectra for each of the predicted "signpost" structures, and identified several key spectral features which could be used to interpret a future time-resolved x-ray absorption experiment.