Charge transfer rates at a bio-inorganic interface

We have investigated the role of molecular bridges in determining the electronic structure and transfer rates at interfaces in which natural or expanded guanine is attached through a thiol bond to a Au(111) surface as a model for charge injection at the DNA@Au interface. Our study is based on van der Waals-corrected ab initio density functional theory calculations. We have considered two linkers with different length and chemistry. We find that the shorter linker allows for a larger electronic coupling between the metal and the guanine, with a modulation of 3 orders of magnitude. The aromatic size expansion of guanine further enhances the electronic coupling by a factor of 2. Our findings demonstrate that even in the case of potentially through-bond charge transfer, the donor-acceptor distance regulates the electronic coupling. Furthermore, we establish a procedure for computing the donor-acceptor coupling between delocalized metal states and localized molecular states. © 2014 American Chemical Society.