Fe(II)-polypyridines have recently gained a lot of attention as potential chromophores in artificial assemblies for solar energy conversion. The photoactive metal-to-ligand charge transfer states in these complexes, however, undergo ultrafast intersystem crossing (ISC) into the manifold of non-photoactive metal-centered states. The ISC in these systems is very difficult to control, thus limiting their utility. We employ density functional theory and a sparse grid interpolation algorithm to construct potential energy surfaces (PESs) in three dimensions for the photophysically relevant states of the [Fe(tpy)2]2+ complex (tpy = 2,2’;6’,2’’-terpyridine), with the goal to obtain a deeper understanding of the ground and excited state electronic structure of this system. We find that the PESs of all excited electronic states investigated are characterized by low-energy valleys along the tpy rocking angle coordinate. This results in the presence of large low-energy areas around the minimum energy crossing points on the intersection seams of different electronic states and indicates that inclusion of the tpy rocking coordinate is crucial for an adequate description of the PESs and surface crossing seams of [Fe(tpy)2]2+ complex. Finally, we suggest that tuning the energetics of the tpy ligand rocking motion could provide a way to controlling the ISC process in this complex.

Toward controlling the intersystem crossing in Fe(II)-polypyridines

251st National Meeting (2016)

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