Simulations of Photoinduced Charge Transfer in Nanodiamond-Acceptor Complex

CARLOS RAÚL MEDRANO; CRISTIAN GABRIEL SANCHEZ

Buenos Airres

Encuentro; XIX Encuentro de superficies y materiales nanoestructurados - NANO2019; 2019

The time scale of the electronic processes in artificial photosynthetic and photovoltaic devices is on the order of femto- to picoseconds and involves vibronic coupling of electrons and nuclei and also nuclear alleviation to enhance charge separation. Here we present an atomistic description of the photoexcited electron dynamics in a noncovalently bonded system formed by an hydrogenated nanodiamond as donor and a perylene diimide as an acceptor using the TD-DFTB method provided by the dftb+ code. The complex shows extremely fast charge transfer, separation, and stabilization within 90 fs (see figure 1). This stabilization is purely electronic in nature. To the best of our knowledge, these results show for the first time that it is possible to stabilize charge without polaron formation or nuclear relaxation, reaching a steady state enhanced by a pure electronic reorganization. A trap-door like mechanism is proposed by which the charge-transfer state is stabilized electrostatically in a dynamic fashion by the charge-separation-induced detuning of donor and acceptor states. The mechanism requires the combination of a donor−acceptor pair with very different chemical hardness. This difference in response between the two systems provides the driving force for the purely electronic stabilization of the charge-transfer state ​[1]​. This work also includes a study of the influence of the nuclear motion in the charge transfer mechanism by performing Ehrenfest dynamics simulations. These calculations show an impact in the amount of charge transferred but it does not seem to affect the proposed mechanism. This phenomenon could be extremely useful in electronic applications where the efficient irreversible charge separation is critical, like light-harvesting devices.