Molecular and Electronic Structure in the Metal-to-Ligand Charge Transfer Excited States of fac-[Re(4,4‘-X₂bpy)(CO)₃(4-Etpy)]⁺* (X = CH₃, H, Co₂Et). Application of Density Functional Theory and Time-Resolved Infrared Spectroscopy

Abstract

Density functional theory (DFT) calculations have been conducted on the ground and metal-to-ligand charge transfer (MLCT) excited states of the series fac-[Re(4,4′-X 2 bpy)(CO) 3 (4-Etpy)](PF 6 ) (X ) CH 3 , H, and CO 2 Et; 4-Etpy is 4-ethylpyridine). The energy gap varies across this series, influencing excited-state geometries and electronic structures. The DFT calculations assist in assigning ν(CO) bands in the infrared and give insight into variations in the experimental values. The predicted bond length and angle changes in the excited state point to the importance of Re-CO σ bond polarization in the excited states as well as π*(4,4′-X 2bpy)-π*(CO) mixing suggested previously.

Ultrafast Excited State Dynamics Controlling Photochemical Isomerization of N‐Methyl‐4‐[trans‐2‐(4‐pyridyl)ethenyl]pyridinium Coordinated to a {ReI(CO)3(2,2′‐bipyridine)} Chromophore

“…At lower wavenumbers, a broad feature occurs between 1980 and 2030 cm À1 . It is composed of several bands due to A'(2) vibrations [63,64] of 3 MLCT states (C) and A'(1) vibrations of IL states (D, E). Another band due to A'' vibration [63,64] of the 3 MLCT states is seen at about 1965 cm À1 (F).…”

Relativistic effects in spectroscopy and photophysics of heavy-metal complexes illustrated by spin–orbit calculations of [Re(imidazole)(CO)3(phen)]+

“…Thus, MLCT states always involve depopulation of carbonyl * orbitals and should be viewed as Re I (CO) 3 → bpy CT. The *(CO) electronic depopulation upon excitation is clearly manifested by shifts of (CO) vibrations to higher energies [9,[12][13][14]22,24,[55][56][57][58][59]. Mixing of MLCT and L → N ∧ N LLCT characters is especially strong in complexes containing donating ligand L (halides, NCS − , amides, phosphides, alkoxides, thiolates, imidazole, etc.)…”

Photophysical properties and computational investigations of tricarbonylrhenium(I)[2-(4-methylpyridin-2-yl)benzo[d]-X-azole]L and tricarbonylrhenium(I)[2-(benzo[d]-X-azol-2-yl)-4-methylquinoline]L derivatives (X=N–CH3, O, or S; L=Cl−, pyridine)

“…7c and d. The orbital H-1 has a reduced Re d -p * (CO) character, in fact there is a consistent migration of electronic amplitude onto the Me-pyridine ring of the mpbN ligand. This mixing between the HOMO and LUMO orbitals accounts for the Re-N(2) (0.11 Å for 8) and Re-N(1) (0.06 Å for 8) distance shortening, as reported in Table 7 [45]. Partial oxidation of the metal center gives a reduction in CO back-bonding and thus a related increase in the rbond interaction with the nitrogen-ligands.…”