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-F₂). Upon fs Soret band excitation at ~400 nm, the energy relaxed almost completely to 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.

Tuning the photophysical properties of iron-based transition-metal complexes is crucial for their employment as photosensitizers in solar energy conversion. For the optimization of these new complexes, a detailed understanding of the excited-state deactivation paths is necessary. Here, we report femtosecond transient mid-IR spectroscopy data on a recently developed octahedral ligand-field enhancing [Fe(dqp)₂]²⁺ (C1) complex with dqp = 2,6-diquinolylpyridine and prototypical [Fe(bpy)₃]²⁺ (C0). By combining mid-IR spectroscopy with quantum chemical DFT calculations, we propose a method for disentangling the ⁵Q₁ and ³T₁ multiplicities of the long-lived metal-centered (MC) states, applicable to a variety of metal-organic iron complexes. Our results for C0 align well with the established assignment toward the ⁵Q₁, validating our approach. For C1, we find that deactivation of the initially excited metal-to-ligand charge-transfer state leads to a population of a long-lived MC ⁵Q₁ state. Analysis of transient changes in the mid-IR shows an ultrafast sub 200 fs rearrangement of ligand geometry for both complexes, accompanying the MLCT → MC deactivation. This confirms that the flexibility in the ligand sphere supports the stabilization of high spin states and plays a crucial role in the MLCT lifetime of metal-organic iron complexes.

The orientation of the Q_y transition dipole moment (tdm) in Chlorophyll a (Chl a) is a fundamental parameter for optimizing energy transfer in light harvesting systems. Here, we apply polarization resolved transient VIS-pump/IR-probe and 2D-IR spectroscopy in combination with density functional theory (DFT) calculations to determining the orientation of the Q_y tdm for hexacoordinated Chl a. Analysis of the 2D-IR spectra provide a comprehensive study of the C═O vibrations, allowing us to refine the modeling of the vibrational tdm (vtdm) vectors. Polarization resolved transient IR spectra provide relative angles between the Q_y tdm and different probed vtdms, which determine cones of possible orientations of the Q_y tdm. Calculating the intersection of three cones from linearly independent vtdm vectors, we determine the orientation of the Q_y tdm. We find that the Q_y tdm for hexacoordinated Chl a is oriented along the y-axis of the macrocycle, exhibiting only a small angular deviation within -1° to 4°.