Excited State Dynamics of Isocyano Rhenium(I) Phenanthroline Complexes from Time‐Resolved Spectroscopy

Abstract

The photophysical processes in a series of isocyano Re(I) phenanthroline complexes {[Re(CNR)n(CO)4‐n(phen)](PF6); n=2, 3, 4, R=2,6‐(iPr)2C6H3‐ or tBu‐ (n=2)} in acetonitrile have been studied by resonance Raman spectroscopy, transient resonance Raman spectroscopy, and femtosecond / nanosecond transient spectroscopy to elucidate the nature of their electronic transitions and emissive excited state(s). The kinetics of the intersystem crossing, vibrational relaxation and radiative decay of the metal‐to‐ligand charge transfer {MLCT [dπ(Re)→π*(phen)]} excited state have also been determined.

Optically Controlled Electron Transfer in a ReI Complex

“…This agrees surprisingly well with the S 0 → S 4 transition which according to DFT calculations has 77 % MLCT and 19 % ILCT character. The broadband ESA with peak at 450 nm seen at later times after excitation and subsequent ILCT dynamics, seems to be characteristic of a whole class of [Re(CO) 3 (α‐diimine)Cl] complexes, which is associated with the formation of a long‐lived triplet MLCT state via intersystem crossing as previously observed in Re I complexes [6b, c, g, 8a, c, 13] . Remarkably, the GSB signal in a range from 520 to 600 nm, which is assigned to the HOMO–LUMO transition with a charge flow from the TTF to DPPZ moieties, persists along with the triplet state ESA even after the back electron transfer following ILCT.…”

Design and Synthesis of Luminescent Bis(isocyanoborato) Rhenate(I) Complexes as a Selective Sensor for Cyanide Anion

“…In the crystal structure, the rhenium metal center adopted a distorted octahedral geometry with bite angles of phenanthroline ligand of about 75.6°, which is commonly observed in other related rhenium­(I) diimine complexes. ,, This is due to the steric requirement of the bidentate chelating phenanthroline ligand. For two isocyanoborate ligands, they are slightly deviated from linearity with the angles of CN–B in the range of 168.7–175.5°.…”

“…This is suggestive of a stronger π-backbonding interaction from dπ­(Re) orbital to π*­(CO) orbital due to the greater electron richness of metal center in these anionic rhenate complexes. In addition to these CO stretches, 1a and 1b also exhibit strong CN stretches at higher frequency, ranging from 2133 to 2151 cm –1 , comparable with those in the reported isocyano rhenium­(I) complexes and other isocyanoborato metal complexes. , Similarly, CN stretching frequencies in these bis­(isocyanoborato) rhenate­(I) complexes are lower than those of the neutral isocyanoborato complexes (2176–2210 cm –1 ). , …”

“…This is probably the result of the π-backbonding interaction from dπ­(Re) orbital to π*­(CN) orbital of the isocyanoborate ligands. The metal–ligand bond distances [Re–CO (1.90 Å) and Re–CNR (2.06 Å)] and the bond distances of CN (1.15 Å) and N–B (1.54 Å) are in the range typically reported in related Re­(I) complexes. ,,, …”

Temperature Dependent Emission Properties of ReI Tricarbonyl Complexes with Dipyrido-Quinoxaline and Phenazine Ligands

“…20,21 The useful photochemical and photophysical properties of these complexes arise from different classes of excited states, including metal-to-ligand charge transfer (MLCT), ligand-to-ligand charge transfer (LLCT), ligand-to-metal charge-transfer (LMCT), intraligand (IL) and metal-centered (MC) states, which the dynamics have been object of detailed experimental and theoretical studies. 1,[22][23][24][25] Among the different polypyridyl…”