Ultrafast spin crossover photochemical mechanism in [Fe(2,2'−bipyridine)3]2+ revealed by quantum dynamics

Abstract

The role of triplet intermediates in the photoinduced spin crossover reaction of [FeII(2,2'-bipyridine)3]2+ is still under debate. Employing quantum dynamics, we show that the metal-centered (MC) triplets are responsible for the transfer to the quintet high-spin state. This photochemical pathway is made possible thanks to bipyridine stretching vibrations, facilitating the transfer between the initial metal-ligand charge transfer (MLCT) states to the MC triplets. These results show the central role of ligands in modulating the excited state spectrum and the photochemical mechanism, opening the route for increased metal-centered lifetime that increases the effciency of iron-based photocatalysts.

Ultrafast Electronic Relaxation in Aqueous [Fe(bpy)3]2+: A Surface Hopping Study

“…However, the relative energies among three different spin multiplicities are sensitive to the details of the models. For example, the vertical excitation energies to 3 T 2g lie in a range of 15599–16042 and 19438–21132 cm –1 for the present model and the model in ref , respectively. Therefore, the differences appeared in the details of the computed pathways may originate from the differences of computed potential energy surfaces such as the locations of the crossing points of MLCT/ 5 T 2g and MLCT/ 3 MC, though further investigations are necessary to confirm this.…”

“…Note that the wavepacket quantum dynamics simulations based on 9 selected vibrational modes have been recently performed for the isolated [Fe(bpy) 3 ] 2+ to explore the relaxation mechanism. 29 The model effective Hamiltonian of [Fe(bpy) 3 ] 2+ is described in the previous study, 28 and the details pertinent to this study are briefly outlined here. The basis functions (all the (3d) 6 and (3d) 5 (π*) 1 configurations) of the model effective Hamiltonian matrix H eff are expressed by the Slater determinants Φ composing of the metal 3d atomic orbitals and model orbitals to represent ligand π*, where the 3d and π* are assumed to be orthogonal.…”

“…However, the present emphasis is to obtain insights into the relaxation mechanism by explicitly dealing with the multiple excited states and all the nuclear degrees of freedom. Note that the wavepacket quantum dynamics simulations based on 9 selected vibrational modes have been recently performed for the isolated [Fe­(bpy) 3 ] 2+ to explore the relaxation mechanism …”

“…Note that the wavepacket quantum dynamics simulations based on 9 selected vibrational modes have been recently performed for the isolated [Fe(bpy) 3 ] 2+ to explore the relaxation mechanism. 29 The model effective Hamiltonian of [Fe(bpy) 3 ] 2+ is described in the previous study, 28 and the details pertinent to this study are briefly outlined here. The basis functions (all the (3d) 6 where ES, EX, and CT represent the M−L electrostatic, exchange, and charge-transfer interactions, respectively.…”

“…These points are different from the present results. In the wavepacket quantum dynamics study of the isolated [Fe(bpy) 3 ] 2+ , 29 the possibility of the direct pathway was excluded, and the 3 T 1g was discussed to be the main intermediates. These details are also different from the present results.…”