Using simulated transient absorption spectroscopy (TAS), we perform theoretical investigations of electronic excited state dynamics of polycyclic aromatic hydrocarbons (PAH). In this study, the steady state absorption spectrum of PAH was calculated both by real-time time-dependent density functional theory (RT-TDDFT) and linear-response time-dependent density functional theory (LR-TDDFT). The consistency of spectra from RT-TDDFT and LR-TDDFT is used to resolve the specific transitions in the dynamics process. For the simulated pump laser pulse, an electric field with Gaussian function was used with a carrier frequency tuned to be in resonance with the plasmonic  peak. The probe is an instantaneous broadband electric field, which is represented by a delta function. The transient absorption spectrum was simulated by repeating the procedure with different time delays. For naphthalene, the stimulated emission for the transition from the  peak to the ground state is companied by a transition from the  peak to the  peak.  The effect of nuclear motion in the electronic excited state dynamics is included by considering Ehrenfest dynamics. Different energies and polarizations of the pump laser are simulated to further understand the on/off resonance excitations in the molecules.

Electronic excited state dynamics of Polycyclic Aromatic Hydrocarbons (PAH) studied by simulated transient absorption spectroscopy

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