The concept of finite temperature Wigner phase-space sampling allowing the population of vibrationally excited states is introduced and employed to study temperature effects on the absorption spectrum of 2-nitronaphtalene (2NN) and its relaxation dynamics. It is found that, despite the fact that the general deactivation mechanism of 2NN after light irradiation does not change with increasing temperature, i.e., after excitation to the singlet manifold, 2NN deactivates via internal conversion in less than 100 fs and then undergoes intersystem crossing to the triplet manifold before decaying to the lowest triplet state in less than 150 fs, the intersystem crossing rate increases at higher temperatures. This increase is attributed to the appearance of a new deactivation pathway, which is not operative at lower temperatures. The present example illustrates that appropriate initial conditions beyond the idealized temperature of 0 K are indispensable to obtain reliable excited state mechanisms, which can be then related to experimental conditions.

Density functional theory is an efficient computational tool to investigate photophysical and photochemical processes in transition metal complexes, giving invaluable assistance in interpreting spectroscopic and catalytic experiments. Optimally-tuned range-separated functionals...

Density functional theory is an efficient computational tool to investigate photophysical and photochemical processes in transition metal complexes, giving invaluable assistance in the interpretation of spectroscopic and catalytic experiments. Optimally-tuned range-separated functionals are particularly promising, as they were created to cure some of the fundamental deficiencies present in approximate exchange-correlation functionals. In this paper, we scrutinize the selection of optimally tuned parameters and its influence on the excited state dynamics, using the example of the iron complex [Fe(cpmp)_2 ]^{2+} with push-pull ligands. Various tuning strategies are contemplated, based on pure self-consistent DFT protocols, as well as on the comparison with experimental spectra and multireference CASPT2 results. The two most promising sets of optimal parameters are then employed to carry out nonadiabatic surface-hopping dynamical simulations. Intriguingly, we find that the two sets lead to very different relaxation pathways and timescales, showcasing the complexity of iron-complexes excited state landscapes and the difficulty of obtaining an unambiguous parametrization of long-range corrected functionals without experimental input.