Excited State Time-Resolved Vibrational Dynamics: the Challenge of Charge Transfer Complexes

Charge transfer -CT- reactions are ubiquitous processes in nature. Photoexcited systems can be monitored to modulate the process and to rationally design photosensitive materials. Current vibrational spectroscopies provide experimental data with high time resolution, although the interpretation at molecular level requires the help of theory and computation. In this context, the atomistic description provided by theoretical analysis and ab initio molecular dynamics (AIMD¹) are a valid support. Isolated molecular systems are a good starting point to disentangle the complexity of anharmonicity and for the method's assessment. This contribution focuses on photoinduced CT reactions of benchmark systems showing a complex photophysical behaviour both in ground and excited state. To unravel the vibrational dynamics of key vibrational modes we use a theoretical approach² combining the AIMD simulations to the Wavelet Analysis in both electronic state. We focused vibrational relaxations of several vibrational modes moving towards quantification of the anharmonic coupling especially between high and low frequencies modes.

¹N. Rega,et al. J.Phys.Chem.B; 2004,108 (13); H. Schlegel, et al. J.Chem.Phys.; 2001 114(22)
²N. Rega,et al. Chem.Sci. 2018, 9.5:1126; PCCP, 10.1039/C8CP04707C, 2018