Mechanochemical control of photoinduced processes

Resum

This thesis is focused on the study of photoinduced processes under external forces. Specifically, the results could be divided in three sections. In the first one, external forces were applied ti different kind of photoswitches, in order to improve selected properties. The second one concerns the study of the forces applied to the reactive chromophore by the surrounding opsin pocket, forming together the well known rhodopsin photoreactive protein. The last one involves the modulation of photophysical processes, in particular the triplet energy transfer. More in detail, the principal objectives and results of this Thesis are summarized as follows: • Through the application of external forces, selected properties of the norbornadiene-quadricyclane system and of azobenzene were considerably improved. Indeed, both systems were considered for possible applications as a molecular solar-thermal (MOST) system. Especially, by applying the knowledge adquired with our novel methodology, different substituent patterns were proposed. • The accurate investigation of the norbornadiene-quadrcyclane photochemistry. The most relevant coordinates describing all processes were detected and it was demonstrated that it is mandatory to include the dynamic electronic correlation effects and a proper basis set augmentation to include Rydberg states, usually neglected. • An insight on the role of the opsin pocket in the retinal photoisomerization. The preliminary study was focused on the forces exerted by the opsin on its chromophore, in particular on the stretching coordinates of the retinal backbone, where the incoming photon energy is initially dissipated thrugh structural vibrations.. • Design of specific donors and/or acceptors for the Triplet energy transfer process. In particular, the principal coordinates able to modulate the T1-S0 energy gap of porphyrin (an archetypal energy donor) were identified, followed by a proposal of different substitution patterns in order to maximize the yield of this kind of process. • Another kind of Triplet energy transfer was also considered as a possible mechanism to explain vision in dim-light conditions. Especially, it was demonstrated that the energy transfer from photosensitizers to rhodopsin is a possible channel to trigger the retinal photoisomerization.