Mainz 2017 – wissenschaftliches Programm
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MO: Fachverband Molekülphysik
MO 8: Fast Intramolecular Dynamics
MO 8.5: Vortrag
Dienstag, 7. März 2017, 15:45–16:00, N 25
Time-resolved fluorescence studies of a polycyclic tetrazolium compound in solution — •Tom Bolze, Jan-Lucas Wree, and Patrick Nuernberger — Physikalische Chemie II, Ruhr-Universität Bochum, 44780 Bochum
Tetrazolium salts are usually colorless and non-fluorescent, whereas the closely related formazans exhibit a bright range of colors. Since reduction of tetrazolium compounds often leads to formazans, numerous applications have been developed that exploit the color change. However, also photo-oxidation can occur, so that e.g. phenyl-benzo[c]tetrazolo-cinnolinium (PTC), one of the very few known fluorescent tetrazolium compounds, is formed from triphenyl-tetrazolium chloride (TTC) upon irradiation with ultraviolet (UV) light in alcoholic solution.
We investigate the fluorescence dynamics of PTC using time-correlated single-photon counting (TCSPC) and femtosecond fluorescence upconversion. PTC is first generated photochemically by UV excitation of TTC at 265 nm. Our TCSPC results in ethanol disclose an excited-state lifetime of ≈700 ps for PTC after S1 excitation and further indicate additional dynamics on an ultrafast time scale. As is evident in fluorescence upconversion measurements, these faster dynamics occur with a characteristic time constant of 6 ps for S1 excitation, whereas this time constant is significantly longer for S2 excitation, presumably reflecting the dissipation of different amounts of excess energy. Studies in more viscous solvents complement the results, and reaction pathways of excited PTC beyond the radiative one are discussed.