Spektroskopie / Bildgebung

The optically active states in a novel Ruthenium-terpyridine complex displaying an unusually broad and redshifted absorption in the visible range are investigated experimentally and theoretically. While the latter feature renders the complexes promising lead structures for sensitizers in dye-sensitized solar cells, a detailed knowledge on the correlation of structural elements with features in the absorption spectrum is indispensable in order to develop strategies for spectroscopy/theory-guided design of such molecular components. Time-dependent density functional theory including solvent effects is employed to assign the UV-vis absorption and resonance Raman (RR) spectra of unprotonated and protonated forms, providing a detailed photophysical picture of a novel class of Ru-polypyridine-based black absorbers which can be tuned by external pH stimuli. The complexes present two absorption maxima in the visible region, which the calculations assign to MLCT and IL states, respectively. RR simulations are done in resonance with both bands and a good agreement is found with the experiment. The examination of the frontier orbitals and the RR spectra of the MLCT state show that protonation favors a charge transfer excitation to the imidazole ligand.