Photoinduced energy and electron transfer at graphene quantum dot/azobenzene interfaces

Abstract

To respond to the constant miniaturization of modern devices, it is imperative to develop novel classes of hybrid materials with outstanding functionalities. One of the most promising developments in this regard is photoswitchable nanoelectronics, which offer non-invasive structural changes via irradiation. Azobenzenes, in particular, represent a widely investigated group of compounds due to their reversible photoisomerization and flexibility to introduce modifications by functionalizing the aryl ring. Here, an interface consisting of graphene quantum dots (GQDs) and a pyrene functionalized azobenzene (AZO) is built and investigated to unravel the energy and charge transfer dynamics at play. The influence of the conformation, isomerization and thermal effects on the photophysics is described using a multiscale computational approach coupled to electronic structure calculations. By computing the photoinduced energy and charge transfer rates we found that the small exciton reorganization energy and favorable alignment of the energy levels at the interface favor excitation energy transfer. A significant increase of photoinduced hole transfer from AZO to GQDs is observed when thermal effects are considered. Moreover, these photoinduced processes for the azobenzene molecules in their trans configuration are always faster than those related to the cis isomer. This is due to a favorable overlap and a stronger interaction of the trans isomer, considered the active state, with the GQDs. On the other hand, the cis configuration, featuring slower photoinduced energy and charge transfer processes, can be considered as the inactive species. Nevertheless, its contribution to the overall photophysics remains non-negligible.