CONICET | Buscador de Institutos y Recursos Humanos

The time scale of the electronic processes in artificial photosynthetic andphotovoltaic devices is on the order of femto- to picoseconds and involves vibronic couplingof electrons and nuclei and also nuclear alleviation to enhance charge separation. Here wepresent an atomistic description of the photoexcited electron dynamics in a noncovalentlybonded system formed by an hydrogenated nanodiamond as donor and a perylene diimide asan acceptor. The complex shows extremely fast charge transfer, separation, and stabilizationwithin 90 fs (see figure 1). This stabilization is purely electronic in nature. To the best of ourknowledge, these results show for the first time that it is possible to stabilize charge withoutpolaron formation or nuclear relaxation, reaching a steady state enhanced by a pure electronicreorganization. A trap-door like mechanism is proposed by which the charge-transfer state isstabilized electrostatically in a dynamic fashion by the charge-separation-induced detuning ofdonor and acceptor states. The mechanism requires the combination of a donor−acceptor pairwith very different chemical hardness. This difference in response between the two systemsprovides the driving force for the purely electronic stabilization of the charge-transfer state.Another requisite is that the donor has a manifold of states initially in tune with the acceptoroptical gap that can transfer charge; this manifold acts as a reservoir that can fill the holewhile detuning. The hard system is then also required to be a nanosystem with a large densityof states in tune with the acceptor. This phenomenon could be extremely useful in electronicapplications where the efficient irreversible charge separation is critical, like light-harvesting1Keywords . Ultrafast Charge Transfer, Nanodiamonds, Light-Harvesting Devices References.[1] Medrano, Carlos R. and Sánchez ,G. Cristián, J. Phys. Chem. Lett. 2018, 9, 3517 devices.

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