Excited states and dynamics of functional Re(I) complexes embedded in metalloproteins

In this project the excited states and the photoinduced dynamics of Rhenium(I) complexes embedded in metalloproteins will be investigated theoretically. Depending on the biological environment and depending on the ligands which functionalize the Re(I) center, these metal complexes can exhibit different functionalities, i.e. they can isomerize, trigger electron transfer or simply emit light. Ultrafast laser experiments have been performed on such systems; however, a mechanistic description of the photoinduced processes is still lacking. This project, therefore, is aimed at discovering and rationalizing the effects of the environment on the photochemistry and photophysics of this family of complexes. Such understanding is fundamental to advance the design of photosynthetic devices, as well as many other systems with applications for material science and molecular biology. To this aim, novel theoretical tools and multi-scale computational strategies will be developed through the combination of three groups with complementary expertise: (1) the calculation of electronically excited states (Strasbourg), (2) the simulation of dynamical processes with quantum (Strasbourg) and semi-classical (Vienna) methods, and (3) the description of biological environments (Nancy). While obtaining specific understanding for molecular systems with experimental interest, the planned consortium will deliver unique methodologies general applicable in the field of photonics. The planned objectives cannot be achieved by a single team. Instead, this consortium is designed to gather complementary know-how in different competences and will allow for synergetic advances, especially in the field of method development.

The aim of this project was to model and simulate light-responsive transition metal complexes in complex bio-environments, such as proteins. In particular, the focus of research was to calculate excited states and the photoinduced dynamics of Re (I) complexes, which experimentally are employed embedded in metallo-labeled mutants of a blue copper protein. The Re (I)-protein system is fascinating because depending on the surrounding ligands and on the environment, specific functions, such as electron transfer triggering, luminescent probing, or isomerization, can in principle be achieved. Given the intricacies of the system, in close collaboration with the partner research groups in Strasbourg and Nancy, we developed new computational approaches that allowed us to investigate the system with increasing degrees of complexity in an efficient and accurate manner. Synergies were exploited between the three groups, which used, developed, extended, and combined complementary techniques involving molecular mechanics from the group in Nancy, quantum dynamics expertise from the group in Strasbourg, and trajectory surface hopping dynamics from our group in Vienna. In this fashion, it was possible to simulate for the first time the excited state dynamics of a [Re(CO)3(Phen)(Im)]+ complex in aqueous solution, as well as in the presence of an amino acid embedded in the blue copper protein, and analyze its spin-dynamics and the charge and energy transfer, respectively. Most of the tools developed are general and can be used for any system in the presence of an environment, which will open new avenues of research. Very importantly, all the developed methods are implemented in openly distributed software, such as our dynamics code SHARC, which now is able to simulate dynamics of transition metal complexes in complex environments.