Excited state absorption (ESA) phenomena underlie many optical response properties of molecules and materials, such as saturable and reverse saturable absorption of visible light. Ultrafast transient spectroscopy is providing a wealth of experimental data on ESA and theoretical methods which can predict ESA are of great utility for elucidating the absorbing excited states. We utilized a real-time (RT) time-dependent density functional theory (TDDFT) propagation of excited state density matrices to simulate optical response in the presence of an electric field delta pulse. Excited state densities were obtained at the linear response (LR) TDDFT level of theory. Due to the adiabatic approximation, the LR-TDDFT densities are non-stationary states in the density propagations utilizing ground state functionals. This issue can be mitigated by performing RT-TDDFT propagations without external perturbation, and in our case we remove the dipole fluctuations from the propagations with applied electric field. This method affords full ESA spectra and can be utilized on large systems with high density of states. A variety of systems will be discussed including organic chromophores, metalloporphyrins, and oligo-porphyrins. This talk will compare the RT-TDDFT approach to calculating ESA with other methods, such as quadratic response TDDFT, and discuss dependence of the calculated ESA spectra on propagation parameters, basis set, and functional. I will highlight application of the RT-TDDFT method for screening the optical limiting capabilities of reverse saturable absorbing chromophores.

Excited state absorption from real-time time-dependent density functional theory simulations: Predicting molecular optical response by excited state density propagation

253rd National Meeting (2017)

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