Spin-orbit vibronic coupling in jahn-teller systems

The photochemistry of chromophores containing heavy elements is a theoretically and computationally little explored field. Experimentally, the photoinduced decomposition of transition-metal carbonyls, for example, has been of considerable interest in femtochemistry since many years. Transition-metal photochemistry has also served as a testbed for the demonstration of laser control of chemical reactions. Complexes of ruthenium, iridium or other transition metals with aromatic molecules are important chromophores for the photosensitation of photovoltaic cells. The photophysics of many of these complexes has been investigated with femtosecond spectroscopy. Most of these metal-organic complexes exhibit high symmetry (e.g. tetrahedral or octahedral symmetry) and are therefore prone to Jahn–Teller distortions in open-shell electronic states. The high density of excited electronic states in the visible or UV region of the spectrum and the multiple crossings and nonadiabatic couplings of potential-energy (PE) surfaces of the same or different spin-multiplicities render the photochemistry of transition-metal complexes considerably more challenging for theory and computation than the photochemistry of molecules built from first-row atoms.