Absorption Spectroscopy, Emissive Properties, and Ultrafast Intersystem Crossing Processes in Transition Metal Complexes: TD-DFT and Spin-Orbit Coupling.

Absorption spectroscopy, emissive properties, and ultrafast intersystem crossing processes in transition metal complexes are discussed in the light of recent developments in time-dependent density functional theory (TD-DFT), spin-orbit coupling (SOC) effects, and non-adiabatic excited states dynamics. Methodological highlights focus on spin-orbit and vibronic couplings and on the recent strategies available for simulating ultra-fast intersystem crossings (ISC).The role of SOC in the absorption spectroscopy of third-row transition metal complexes is illustrated by two cases studies, namely Ir(III) phenyl pyridine and Re(I) carbonyl bipyridine complexes.The problem of luminescence decay in third-row transition metal complexes handled by TD-DFT linear and quadratic response theories including SOC is exemplified by three studies: (1) the phosphorescence of Ir(III) complexes from the lowest triplet state; (2) the emissive properties of square planar Pt(II) complexes with bidentate and terdentate ligands characterized by low-lying metal-to-ligand-charge-transfer (MLCT) and metal-centered (MC) states; and (3) the ultra-fast luminescence decay of Re(I) carbonyl bipyridine halides via low-lying singlet and triplet charge transfer states delocalized over the bipyridine and the halide ligands.Ultrafast ISC occurring in spin crossover [Fe (bpy)3]2+, in [Ru (bpy)3]2+, and [Re (Br)(CO)3(bpy] complexes are deciphered thanks to recent developments based on various approaches, namely non-radiative rate theory within the Condon approximation, non-adiabatic surface hopping molecular dynamics, and quantum wave packet dynamics propagation.