Ricerc@Sapienza

Photophysical and photochemical processes are often ruled by molecular vibrations coupled to specific electronic states. Dissecting the corresponding, often overlapping, spectroscopic signals from different electronic states is a challenge hampering their interpretation. This is crucial, for example, to understand photosynthesis, where interactions between electronic and vibrational degrees of freedom play a major role for rapid and efficient energy transfer. Despite huge effort from different research fields, assigning vibrational features to the related electronic states remains a demanding task, preventing the development of competitive bio-inspired artificial harvesting systems. In order to tackle this problem, the present research proposes development of a chirp modulator for Impulsive Stimulated Raman Spectroscopy (ISRS), a powerful technique able to coherently stimulate and record Raman-active modes using broadband pulses. Building on our recent theoretical predictions [Monacelli L. et al, J. Phys. Chem. Lett., 8, 966 (2017)], here we aims to experimentally demonstrate that tuning the chirp of the femtosecond pulse that probes the vibrational oscillations in ISRS affects the relative phase between the different contributions to the signal, leading to constructive or destructive interference. Using probe chirp as a novel control knob allow us to selectively enhance desired vibrational features and distinguish spectral components arising from different excited states. The proposed experimental scheme will be applied to the study of excited state vibrational spectra of LH2 complexes in purple bacteria.