How the environment can tune the energy, the coupling, and the ultrafast dynamics of interacting chromophores: the effect of hydrogen-bonds

The role of hydrogen bonds (H-bonds) is central to understanding microscopic structures and functions in many functional biological and artificial materials. H-bonds stabilize and determine the 3D structure of biological macromolecules such as proteins and DNA and can play an essential role in determining the reactivity of the active site of enzymes. The directional nature of H-bonds has important implications not only for the final geometry of the complexes but also for their electronic properties.

In this work, we compared a biological pigment-protein complex, the Water-Soluble Chlorophyll-binding Protein (WSCP), and an artificial H-bonded BODIPY dimer, in order to verify how the presence of H-bond could affect the ultrafast dynamic relaxation in the excited state. 2D Electronic Spectroscopy is applied for this purpose since it allows to follow the ultrafast dynamics of complex systems, providing information on the temporal evolution of both coherent and non-coherent processes with a time resolution in the order of femtoseconds.

For both the systems, the directional nature of H-bonds has important implications for the electronic properties. In WSCP, it has been found that the transition dipole moments, the electronic coupling and the excitonic energy gaps are tuned by the presence of specific and directional interactions between the protein backbone and the formyl group on the Chl b moiety.[1] In the BODIPY dimer, the H-bonds activate new ultrafast dynamic channels in the relaxation dynamics of the dimer involving intra- and inter-molecular mechanisms.[2]

These findings suggest that the design of H-bonded structures is a particularly powerful tool to drive the ultrafast dynamics in complex materials since it implies the possibility of tuning the photophysics and the transport properties of complex systems by engineering specific interactions with the surroundings.

[1] E. Fresch, E. Meneghin, A. Agostini, H. Paulsen, D. Carbonera, and E. Collini, J. Phys. Chem. Lett. 11, 1059 (2020)

[2] E. Fresch, N. Peruffo, M. Trapani, M. Cordaro, G. Bella, M.A Castriciano and E. Collini, J. Chem. Phys. 154, 084201 (2021)

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