Spin–Orbit Treatment of UV–vis Absorption Spectra and Photophysics of Rhenium(I) Carbonyl–Bipyridine Complexes: MS-CASPT2 and TD-DFT Analysis

Abstract

The lowest-lying spectral transitions in [ReX(CO)(3)(bpy)] (X = Cl, Br, I; bpy = 2,2'-bipyridine) complexes were calculated by means of spin-orbit time-dependent density functional theory (SO-TD-DFT) and spin-orbit multistate complete active space second-order perturbation theory (SO-MS-CASPT2). Computational results are compared with absorption spectra measured in different solvents and used to qualitatively explain the temperature dependence of the phosphorescence decay parameters that were measured for the whole series of complexes. Spin-orbit excited-state calculations interpret their electronic absorption spectra as arising from a bunch of spin mixed states with a singlet component of only 50-90% (depending on the halide), and attribute the phosphorescence decay to thermal population of spin-mixed states with a substantial singlet character.

Spin-Vibronic Quantum Dynamics for Ultrafast Excited-State Processes

“…18,19,44−46 By combining spectroscopic measurements and CASSCF/MS-CASPT2 and TD-DFT calculations, we have shown that whereas both spinfree and spin−orbit quantum chemical calculations simulate UV−vis electronic spectra of [Re(X)(CO) 3 bpy)] (X = Cl, Br, or I) complexes in a reasonable agreement with experiment, they give a very different interpretation of the absorption bands and only the SO treatment can account for the observed spectral features. 44,46 Going further we computed the spin− orbit coupled TD-DFT potential energy curves as a function of the Re−X bond elongation, as well as of the Re−X bond stretching modes, for the electronic ground state and the lowest excited states of [Re(X)(CO) 3 (bpy)] (X = Cl, Br, or I) taking into account solvent effects. 19,46 When SOC is activated the five lowest electronic excited states, S1, S2, T1, T2, and T3, the electronic densities of which are depicted in Scheme 1 for [Re(Br)(CO) 3 (bpy)], generate 11 "spin−orbit" states of mixed metal-to-ligand-charge-transfer MLCT/halide-LCT character within 0.5 eV, see Scheme 2 and Figure 2 further below.…”

“…44,46 In the Pauli approximation, the electronic Hamiltonian H el is expressed as the sum of the nonrelativistic (electrostatic), H es , and the "spin−orbit", H SO , Hamiltonians:…”

Electron transfer dynamics and excited state branching in a charge-transfer platinum(ii) donor–bridge-acceptor assembly

“…The identical absorption maxima for 1 and 2, which are only slightly different compared to the Cl precursor 3, and the absence of any >350 nm absorbances in the NAP-free building block 4, confirm the lack of PTZ involvement in the initial excitation event. 89,92,93 Using the transient absorption and infrared spectroscopic data, and extracting energy levels of the electronic states from cyclic voltammetry and emission data, one can construct an energy level diagram for 1 as presented in Fig. Following an initial ultrafast electronic evolution on the 0.5-1 ps timescale, strong stimulated emission is observed at the same spectral position as that assigned to the emission from a [Ph-CuC-Pt-CuC]-to-NAP charge transfer excited state in the steady-state emission spectra.…”

A general method to describe intersystem crossing dynamics in trajectory surface hopping

“…A number of studies have used quantum wavepacket dynamics, where inclusion of SOC is straightforward; however, these studies are usually restricted to few degrees of freedom. Examples include dihalogens in argon matrices, [80][81][82] transition-metal complexes, [83][84][85][86][87][88][89][90][91][92][93][94][95] and collision reactions. [96] Further, quantum dynamical studies investigated ISC in benzene, [97] hydrogen fluoride, [98] and sulphur dioxide.…”