Optical Activity of Spin‐Forbidden Electronic Transitions in Metal Complexes from Time‐Dependent Density Functional Theory with Spin‐Orbit Coupling

Abstract

The calculation of magnetic transition dipole moments and rotatory strengths was implemented at the zeroth-order regular approximation (ZORA) two-component relativistic time-dependent density functional theory (TDDFT) level. The circular dichroism of the spin-forbidden ligand-field transitions of tris(ethylenediamine)cobalt(III) computed in this way agrees very well with available measurements. Phosphorescence dissymmetry factors g lum and the corresponding lifetimes are evaluated for three N-heterocyclic-carbene-based iridium complexes, two of which contain helicene moieties, and for two platinahelicenes. The agreement with experimental data is satisfactory. The calculations reproduce the signs and order of magnitude of g lum , and the large variations of phosphorescence lifetimes among the systems. The electron spin contribution to the magnetic transition dipole moment is shown to be important in all of the computations.

Low-Temperature Luminescence in Organic Helicenes: Singlet versus Triplet State Circularly Polarized Emission

“…Triplet emission lifetimes and dipole strengths were determined from TD-DFT calculations including the spin–orbit interaction. ,− These calculations used the 2021 release of the Amsterdam Density Functional (ADF) program . The CAM-B3LYP functional, DZP (DZ on hydrogens) Slater-type basis sets, and the zeroth-order regular approximation (ZORA) two-component relativistic Hamiltonian were employed for these calculations.…”

“…47 The CAM-B3LYP functional, DZP (DZ on hydrogens) Slater-type basis sets, 48 and the zeroth-order regular approximation (ZORA) two-component relativistic Hamiltonian were employed for these calculations. Magnetic transition dipole moments and rotatory strengths for the T 1 − S 0 transitions were obtained with a recent modification of ADF, 44 implementing the CDSPECTRUM keyword for SO-TDDFT calculations. This code has been available since the 2021 release and will be documented in detail in future releases.…”

Helical Induction, Chiroptical Properties, and Quantitative Prediction of the Dissymmetry Factor on the Circularly Polarized Phosphorescence of Iminopyrrolyl Platinum(II) Complexes

“…Thus far, there have only been a few theoretical studies, e.g., the estimation of the absolute |g| values of the lowest triplet states 28 and g values of CPP. 29 This is owing to the complexity of the triplet state, that is, spin-disallowed character and three existing triplet sublevels with different magnetic quantum numbers. The development of novel chiral complexes and the theoretical analysis of CPP are significant and urgent to unveil the chiroptical properties of the triplet state.…”

“…In recent years, chiral platinum, − iridium, − ruthenium, rhenium, and chromium , complexes bearing chiral and achiral ligands have been reported as circularly polarized phosphorescence (CPP) emitters. In contrast to the octahedral complexes, the reported chiral Pt­(II) complexes possess unique helicene, − , binaphthyl, , cyclophane, , cylinder-like, and other second-order , chiral structures owing to the square planar coordination, leading to diverse and rich photophysical properties (Figure S1).…”

“…Despite the significant progress in the field, mechanistic studies of CPP to control the g value remain insufficient. Thus far, there have only been a few theoretical studies, e.g., the estimation of the absolute | g | values of the lowest triplet states and g values of CPP . This is owing to the complexity of the triplet state, that is, spin-disallowed character and three existing triplet sublevels with different magnetic quantum numbers.…”