Ultrafast Solution-Phase Photophysical and Photochemical Dynamics of Hexaiodobismuthate(III), the Heart of Bismuth Halide Perovskite Solar Cells.

The ultrafast relaxation pathways in a hexaiodide bismuth(III) complex, BiI, excited at 530 nm in acetonitrile solution are studied by means of femtosecond transient absorption spectroscopy supported by steady-state absorption/emission measurements and DFT computations. Radiationless relaxation out of the Franck-Condon, largely metal-centered (MC) triply degenerate T state (46 ± 19 fs), is driven by vibronic coupling due to the Jahn-Teller effect in the excited state. The relaxation populates two lower-energy states: a ligand-to-metal charge transfer (LMCT) excited state of π I(5p) → Bi(6p) nature and a luminescent "trap" A(P) MC state.

Ultrafast dynamics in LMCT and intraconfigurational excited states in hexahaloiridates(iv), models for heavy transition metal complexes and building blocks of quantum correlated materials.

The population and structural dynamics of IrCl is studied in acetonitrile and aqueous solutions in comparison to isoelectronic IrBr using ultrafast broadband, dispersed transient absorption, with both octahedra excited with 85 fs pulses at four different wavelengths, encompassing the first seven t-based electronic states. Ligand-to-metal charge transfer (LMCT) 420 or 490 nm excitation of IrCl into U'(T) + E''(T) states, superimposed due to Ham effect, or U'(T), respectively, leads to symmetry lowering due to Jahn-Teller effect in these excited states with the subsequent 100 fs decay into U'(T). This first LMCT state is formed vibrationally coherent in the 104 cm t (scissor) or 243 cm e (out-of-phase-stretch) Jahn-Teller modes for the respective excitation wavelength.