Photoinduced electron transfer in a dichromophoric peptide: a numerical experiment

In this study, we have applied a theoretical–computational methodology, developed in our laboratory and based on molecular dynamics simulations and quantum-chemical calculations, for modelling the kinetics of photoinduced electron-transfer (ET) reaction between two chromophores covalently linked to a peptide in acetonitrile solution. The results, in satisfactory agreement with the experimental data, reveal that the intensity and the fluctuation of the electric field exerted by the peptide onto the two chromophores, acting as the acceptor and the donor, is crucial for the efficiency of the ET reaction. The distance between the two chromophores also turns out to be very important for the ET reaction. In fact, at distances lower than 1.0 nm the reaction is found to proceed with a very high efficiency which drastically reduces when the two partners move away at higher distances. This is also supposed to represent the origin of the biexponential kinetic feature experimentally found and reproduced by our study. By a methodological point of view this study provides an example of a theoretical-computational perspective alternative to the most commonly utilized procedures for simulating photoinduced ET reactions in very complex systems which represent the molecular engine of the solar energy production.