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

Dual fluorescence in 4-(dimethylamino)-benzonitrile (DMABN)andits derivatives in polar solvents has been studied extensively forthe past several decades. An intramolecular charge transfer (ICT)minimum on the excited state potential energy surface, in additionto the localized low-energy (LE) minimum, has been proposed as a mechanismfor this dual fluorescence, with large geometric relaxation and molecularorbital reorganization a key feature of the ICT pathway. Herein, wehave used both equation-of-motion coupled-cluster with single anddouble excitations (EOM-CCSD) and time-dependent density functional(TDDFT) methods to investigate the landscape of excited state potentialenergy surfaces across a number of geometric conformations proposedas ICT structures. In order to correlate these geometries and valenceexcited states in terms of potential experimental observables, wehave calculated the nitrogen K-edge ground and excited state absorptionspectra for each of the predicted "signpost" structuresand identified several key spectral features that could be used tointerpret a future time-resolved X-ray absorption experiment.