Photophysics of a copper phenanthroline elucidated by trajectory and wavepacket-based quantum dynamics: a synergetic approach

On-the-fly excited state molecular dynamics is a valuable method for studying non-equilibrium processes in excited states and is beginning to emerge as a mature approach much like its ground state counterparts. In contrast to quantum wavepacket dynamics methods, it negates the need for modelling potential energy surfaces, which usually confine nuclear motion within a reduced number of vibrational modes. In addition, on-the-fly molecular dynamics techniques are easily combined with the atomistic description of the solvents (through the QM/MM approach) making it possible to explicitly address the effect of the environment. Herein, we study the nonadiabatic relaxation of photoexcited [Cu(dmp)2]+ (dmp = 2,9-dimethyl-1,10-phenanthroline) using QM/MM Trajectory Surface Hopping (TSH). We show that the decay of the initially excited singlet state into the lowest singlet (S1) state occurs within 100 fs, in agreement with previous experiments, and is slightly influenced by the solvent. Using a principal component analysis (PCA), we also identify the dominant normal modes activated during the excited state decay, which are then used to design the vibronic Hamiltonian for quantum wavepacket dynamics simulations.