Theoretical spectroscopy for unraveling the intensity mechanism of the optical and photoluminescent spectra of chiral Re(I) transition metal complexes

Rami Shafei; Ai Hamano; Christophe Gourlaouen; Dimitrios Maganas; Keiko Takano; Chantal Daniel; Frank Neese

doi:10.1063/5.0153742

Theoretical spectroscopy for unraveling the intensity mechanism of the optical and photoluminescent spectra of chiral Re(I) transition metal complexes

J Chem Phys. 2023 Aug 28;159(8):084102. doi: 10.1063/5.0153742.

Authors

Rami Shafei^{1

2}, Ai Hamano^{3

4}, Christophe Gourlaouen³, Dimitrios Maganas¹, Keiko Takano⁴, Chantal Daniel³, Frank Neese¹

Affiliations

¹ Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, 45470 Mülheim an der Ruhr, Germany.
² Department of Chemistry, Faculty of Science, Beni-Suef University, Salah Salem Str., 62511 Beni-Suef, Egypt.
³ Laboratoire de Chimie Quantique, Institut de Chimie, UMR 7177 CNRS-Université de Strasbourg, 4, Rue Blaise Pascal CS 90032, F-67081 Strasbourg Cedex, France.
⁴ Department of Chemistry and Biochemistry, Graduate School of Humanities and Sciences Ochanomizu University, 2-1-1 Otsuka, Bunkyo-ku, Tokyo 112-8610, Japan.

PMID: 37606333
DOI: 10.1063/5.0153742

Abstract

In this work, we present a computational study that is able to predict the optical absorption and photoluminescent properties of the chiral Re(I) family of complexes [fac-ReX(CO)3L], where X is either Cl or I and L is N-heterocyclic carbene extended with π-conjugated [5]-helicenic unit. The computational strategy is based on carefully calibrated time dependent density functional theory calculations and operates in conjunction with an excited state dynamics approach to treat in addition to absorption (ABS) and photoluminescence (PL), electronic circular dichroism (ECD), and circularly polarized luminescence (CPL) spectroscopies, respectively. The employed computational approach provides, an addition, access to the computation of phosphorescence rates in terms of radiative and non-radiative relaxation processes. The chosen molecules consist of representative examples of non-helicenic (NHC) and helicenic diastereomers. The agreement between theoretical and experimental spectra, including absorption (ABS, ECD) and emission (PL, CPL), is excellent, validating a quantitative interpretation of the spectral features on the basis of natural transition orbitals and TheoDore analyses. It is demonstrated that across the set of studied Re(I) diastereomers, the emission process in the case of NHC diastereomers is metal to ligand charge transfer in nature and is dominated by the easy-axis anisotropy of the emissive excited multiplet. On the contrary, in the cases of the helicenic diastereomers, the emission process is intra ligand charge transfer in nature and is dominated by the respective easy-plane anisotropy of the emissive excited multiplet. This affects remarkably the photoluminescent properties of the molecules in terms of PL and CPL spectral band shapes, spin-vibronic coupling, relaxation times, and the respective quantum yields. Spin-vibronic coupling effects are investigated at the level of the state-average complete active space self-consistent field in conjunction with quasi-degenerate second order perturbation theory. It is in fact demonstrated that a spin-vibronic coupling mechanism controls the observed photophysics of this class of Re(I) complexes.