Ricerc@Sapienza

Vibrations play a crucial role in many photophysical and photochemical processes in which excitations reside on electronically excited states. Specific coupling between electronic and vibrational degrees of freedom rules structural rearrangement events and efficient energy transfer phenomena. However, despite huge efforts from different research fields, assigning vibrational signals from spectroscopic measurements with congested spectra uniquely to a specific electronic state, ground or otherwise, remains a demanding task. In order to tackle this issue, the present research proposes the development of a chirp modulator for Impulsive Vibrational Scattering (IVS), a powerful technique able to coherently stimulate and probe Raman-active modes using femtosecond broadband pulses. Recently, we have theoretically demonstrated that in IVS the signal originates from different physical processes interfering with each other in a mode-specific way. Building on our previous results and on an existing pump-probe setup, here we propose the realization of a femtosecond pulse shaper able to control the chirp of the ultrashort probe pulse, used for real-time monitoring the molecular vibrations in IVS. The proposed experimental scheme will be used for experimentally demonstrating how a fine tuning of the probe chirp can be used as a novel control knob, allowing us to selectively enhance desired vibrational features and to distinguish spectral components arising from different excited states. Harnessing the possibility to assign the pertaining electronic state to a given molecular vibration, we will be able to track the ultrafast dynamics of photosynthetic complexes, in order to address the highly debated case of vibrational relaxation and energy transfer processes in these essential reaction centres.