Ultrafast Electronic Relaxation through a Conical Intersection: Nonadiabatic Dynamics Disentangled through an Oscillator Strength-Based Diabatization Framework

Abstract

We employ surface hopping trajectories to model the short-time dynamics of gas-phase and partially solvated 4-(N,N-dimethylamino)benzonitrile (DMABN), a dual fluorescent molecule that is known to undergo a nonadiabatic transition through a conical intersection. To compare theory vs time-resolved fluorescence measurements, we calculate the mixed quantum-classical density matrix and the ensemble averaged transition dipole moment. We introduce a diabatization scheme based on the oscillator strength to convert the TDDFT adiabatic states into diabatic states of L and L character. Somewhat surprisingly, we find that the rate of relaxation reported by emission to the ground state is almost 50% slower than the adiabatic population relaxation. Although our calculated adiabatic rates are largely consistent with previous theoretical calculations and no obvious effects of decoherence are seen, the diabatization procedure introduced here enables an explicit picture of dynamics in the branching plane, raising tantalizing questions about geometric phase effects in systems with dozens of atoms.

A molecular perspective on Tully models for nonadiabatic dynamics

“…This molecule has been the subject of different studies looking into the details of its ultrafast decay from the photoexcited S 2 state and using different levels of theory for the electronic structure and the nuclear dynamics. 98,[118][119][120] All previous work agreed on the ultrafast relaxation from the S 2 to the S 1 occurring within the first 50 fs of dynamics. This ultrafast decay is also in line with the photodynamics of the parent molecule 4-aminobenzonitrile, studied with MCTDH.…”

Excited-state dynamics of molecules with classically driven trajectories and Gaussians

“…More importantly, TSH-EDC is in good agreement with the AIMS/LR-TDDFT result, showing as expected that AIMS naturally accounts for decoherence effects thanks to its use of coupled TBFs. We note that a previous comparison of A-FSSH/LR-TDDFT with TSH/LR-TDDFT (supporting information of [189]) did not show such a pronounced difference between the dynamics with and without a correction. These simulations, however, used a different way of sampling initial conditions (initial conditions sampled from a ground-state ab initio molecular dynamics) and showed no residual S 2 population after 50 fs of dynamics, in contrast to the other TSH and AIMS simulations.…”

“…DMABN is a molecule famous for its dual fluorescence. Its ultrafast dynamics upon photoexcitation in the second excited electronic state (S 2 ) has been recently studied using TSH/LR-TDDFT [187], TSH/ADC(2) [188], A-FSSH/LR-TDDFT [189] and AIMS/LR-TDDFT [118]. All methods describe an ultrafast relaxation of the S 2 population towards S 1 in less than 50 fs, without a twist of the dimethylamino group (as proposed in an earlier theoretical work [190]).…”

Simulating the Nonadiabatic Relaxation Dynamics of 4-(N,N-Dimethylamino)benzonitrile (DMABN) in Polar Solution

“…Although the kinetic aspects of the relaxation processes of aminobenzonitriles have been the subject of several computational studies, [36][37][38][39][40][41][42][43][44][45] there is still insufficient data to conclusively support any one of the three kinetic models reviewed above. Many of the unanswered questions concern the role (if any) of the RICT structure.…”