Abstract
We report the non-adiabatic dynamics of VIIICl3(ddpd), a complex based on the Earth-abundant first-row transition metal vanadium with a d2 electronic configuration which is able to emit phosphorescence in solution in the near-infrared spectral region. Trajectory surface-hopping dynamics based on linear vibronic coupling potentials obtained with CASSCF provide molecular-level insights into the intersystem crossing from triplet to singlet metal-centered states. While the majority of the singlet population undergoes back-intersystem crossing to the triplet manifold, 1–2% remains stable during the 10 ps simulation time, enabling the phosphorescence described in Dorn et al. Chem. Sci., 2021, DOI: 10.1039/D1SC02137K. Competing with intersystem crossing, two different relaxation channels via internal conversion through the triplet manifold occur. The nuclear motion that drives the dynamics through the different electronic states corresponds mainly to the increase of all metal–ligand bond distances as well as the decrease of the angles of trans-coordinated ligand atoms. Both motions lead to a decrease in the ligand-field splitting, which stabilizes the interconfigurational excited states populated during the dynamics. Analysis of the electronic character of the states reveals that increasing and stabilizing the singlet population, which in turn can result in enhanced phosphorescence, could be accomplished by further increasing the ligand-field strength.
Highlights
The development of photoactive coordination compounds largely focuses on 4d or 5d metals because they o en feature long-lived excited states that can be exploited in multiple applications
We report the non-adiabatic dynamics of VIIICl3(ddpd), a complex based on the Earth-abundant first-row transition metal vanadium with a d2 electronic configuration which is able to emit phosphorescence in solution in the near-infrared spectral region
Luminescence has been observed for homoleptic chromium(III) complexes using the ddpd,[12,13] H2tpda[14] and dqp[15] ligands (ddpd 1⁄4 N,N0-dimethyl-N,N0-dipyridine-2-ylpyridine-2,6diamine; H2tpda 1⁄4 2,6-bis(2-pyridylamino)pyridine; dqp 1⁄4 2,6di(quinolin-8-yl)pyridine), which emit at the beginning of in the near-infrared region of the light spectrum (NIR) at 775, 782, and
Summary
3d-metal complexes of chromium(0),[7] iron(III),[8,9] cobalt(III),[10] and copper(I)[11] exhibit luminescence in the visible region of the light spectrum. A mechanistic understanding of photoluminescence can help identifying the competing non-adiabatic relaxation pathways in a molecule This can enable a better modulation of quantum yields, which leads to design principles for improving luminescence in complexes based on Earth-abundant transition metals. Given its positive trade-off between accuracy and computational cost, TDDFT is likely the most popular method to study transition metal complexes,[31,32] and it has been applied in on-the- y surface hopping studies of other transition-metal complexes.[33,34,35,36,37] TDDFT can become problematic for open-shell systems with degenerate ground states due to its single-reference nature This is the case for pseudooctahedral vanadium(III) complexes, such as VIIICl3(ddpd), which possesses a d2 ground-state electron con guration. This analysis reveals the presence of an important higher-order excitation character in low-lying excited states with
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