Intraligand charge-transfer excited states in Re(I) complexes with donor-substituted dipyridophenazine ligands

Christopher B. Larsen, Holly Van Der Salm, Charlotte A. Clark, Anastasia B.S. Elliott, Michael G. Fraser, Raphael Horvath, Nigel T. Lucas, Xue Zhong Sun, Michael W. George, Keith C. Gordon

Research output: Journal PublicationArticlepeer-review

52 Citations (Scopus)

Abstract

The donor-acceptor ligands 11-(4-diphenylaminophenyl)dipyrido[3,2-a: 2′,3′-c]phenazine (dppz-PhNPh2) and 11-(4- dimethylaminophenyl)dipyrido[3,2-a:2′,3′-c]phenazine (dppz-PhNMe2), and their rhenium complexes, [Re(CO)3X] (X = Cl-, py, 4-dimethylaminopyridine (dmap)), are reported. Crystal structures of the two ligands were obtained. The optical properties of the ligands and complexes are dominated by intraligand charge transfer (ILCT) transitions from the amine to the dppz moieties with λabs = 463 nm (ε = 13 100 M-1 cm-1) for dppz-PhNMe 2 and with λabs = 457 nm (ε = 16 900 M -1 cm-1) for dppz-PhNPh2. This assignment is supported by CAM-B3LYP TD-DFT calculations. These ligands are strongly emissive in organic solvents and, consistent with the ILCT character, show strong solvatochromic behavior. Lippert-Mataga plots of the data are linear and yield Δμ values of 22 D for dppz-PhNPh2 and 20 D for dppz-PhNMe2. The rhenium(I) complexes are less emissive, and it is possible to measure resonance Raman spectra. These data show relative band intensities that are virtually unchanged from λexc = 351 to 532 nm, consistent with a single dominant transition in the visible region. Resonance Raman excitation profiles are solvent sensitive; these data are modeled using wavepacket theory yielding reorganization energies ranging from 1800 cm-1 in toluene to 6900 cm-1 in CH3CN. The excited state electronic absorption and infrared spectroscopy reveal the presence of dark excited states with nanosecond to microsecond lifetimes that are sensitive to the ancillary ligand on the rhenium. These dark states were assigned as phenazine-based 3ILCT states by time-resolved infrared spectroscopy. Time-resolved infrared spectroscopy shows transient features in which Δν(CO) is approximately -7 cm-1, consistent with a ligand-centered excited state. Evidence for two such states is seen in mid-infrared transient spectra.

Original languageEnglish
Pages (from-to)1339-1354
Number of pages16
JournalInorganic Chemistry
Volume53
Issue number3
DOIs
Publication statusPublished - 3 Feb 2014
Externally publishedYes

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Inorganic Chemistry

Fingerprint

Dive into the research topics of 'Intraligand charge-transfer excited states in Re(I) complexes with donor-substituted dipyridophenazine ligands'. Together they form a unique fingerprint.

Cite this