Ultrafast Dynamics of Sb-Corroles: A Combined Vis-Pump Supercontinuum Probe and Broadband Fluorescence Up-Conversion Study

Clark Zahn, Till Stensitzki, Mario Gerecke, Alexander Berg, Atif Mahammed, Zeev Gross, Karsten Heyne
2017 Molecules  
Corroles are a developing class of tetrapyrrole-based molecules with significant chemical potential and relatively unexplored photophysical properties. We combined femtosecond broadband fluorescence up-conversion and fs broadband Vis-pump Vis-probe spectroscopy to comprehensively characterize the photoreaction of 5,10,15-tris-pentafluorophenyl-corrolato-antimony(V)-trans-difluoride (Sb-tpfc-F 2 ). Upon fs Soret band excitation at~400 nm, the energy relaxed almost completely to Q band electronic
more » ... o Q band electronic excited states with a time constant of 500 ± 100 fs; this is evident from the decay of Soret band fluorescence at around 430 nm and the rise time of Q band fluorescence, as well as from Q band stimulated emission signals at 600 and 650 nm with the same time constant. Relaxation processes on a time scale of 10 and 20 ps were observed in the fluorescence and absorption signals. Triplet formation showed a time constant of 400 ps, with an intersystem crossing yield from the Q band to the triplet manifold of between 95% and 99%. This efficient triplet formation is due to the spin-orbit coupling of the antimony ion. to the optimized application of corroles [8, [28] [29] [30] [31] [32] [33] [34] [35] [36] [37] [38] [39] . However, there are only a few in-depth reports tracking the photoreaction of corroles [35, [39] [40] [41] [42] [43] [44] [45] [46] . A combined study on the ultrafast electronic and vibrational dynamics of a brominated corrole system demonstrated intersystem crossing to the triplet manifold with a time constant of 100 ps and a quantum yield of close to one [39] . Whether efficient intersystem crossing can only be achieved by heavy atom insertion at the macrocycle ring or can also be realized by varying the peripheral substituents and/or axial ligands, causing macrocycle distortion and thus leading to changes in the electronic structure of the complex, is not fully understood. Moreover, it is also unclear if the absorption spectra of the triplet and singlet excited states are similar for most corroles or if the spectra are sensitive to metal ions and ligands. It has been reported that excitation of the Soret band at around 400 nm leads to energy relaxation into Q band states between 500 nm and 700 nm within a picosecond, accompanied by the rise of Q band fluorescence [37] . Whether an intersystem crossing takes place during Soret band to Q band transitions is unknown. Here we report a study into the ultrafast electronic dynamics of a 5,10,15-tris-pentafluorophenylcorrolato trianion (tpfc) chelating an antimony metal ion. The antimony corrole is further stabilized by two axial fluorides forming a Sb-tpfc-F 2 complex (see inset of Figure 1 ). The ultrafast dynamics were investigated by a combination of two complementary time-resolved spectroscopy methods: broadband fluorescence up-conversion and broadband absorption spectroscopy. Molecules 2017, 22, 1174 2 of 13 tracking the photoreaction of corroles [35, [39] [40] [41] [42] [43] [44] [45] [46] . A combined study on the ultrafast electronic and vibrational dynamics of a brominated corrole system demonstrated intersystem crossing to the triplet manifold with a time constant of 100 ps and a quantum yield of close to one [39] . Whether efficient intersystem crossing can only be achieved by heavy atom insertion at the macrocycle ring or can also be realized by varying the peripheral substituents and/or axial ligands, causing macrocycle distortion and thus leading to changes in the electronic structure of the complex, is not fully understood. Moreover, it is also unclear if the absorption spectra of the triplet and singlet excited states are similar for most corroles or if the spectra are sensitive to metal ions and ligands. It has been reported that excitation of the Soret band at around 400 nm leads to energy relaxation into Q band states between 500 nm and 700 nm within a picosecond, accompanied by the rise of Q band fluorescence [37] . Whether an intersystem crossing takes place during Soret band to Q band transitions is unknown. Here we report a study into the ultrafast electronic dynamics of a 5,10,15-tris-pentafluorophenylcorrolato trianion (tpfc) chelating an antimony metal ion. The antimony corrole is further stabilized by two axial fluorides forming a Sb-tpfc-F2 complex (see inset of Figure 1 ). The ultrafast dynamics were investigated by a combination of two complementary time-resolved spectroscopy methods: broadband fluorescence up-conversion and broadband absorption spectroscopy.
doi:10.3390/molecules22071174 pmid:28703762 fatcat:6a6iygzqzveuzktlxielmzpuui