Luminescence studies of pyridine .alpha.-diimine rhenium(I) tricarbonyl complexes

• Published in: Inorganic chemistry Vol. 29; no. 21; pp. 4335 - 4340
• Main Authors: Sacksteder, LouAnn, Zipp, Arden P, Brown, Elizabeth A, Streich, Julie, Demas, J. N, DeGraff, B. A
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 01.10.1990
• Subjects: 140505 - Solar Energy Conversion- Photochemical, Photobiological, & Thermochemical Conversion- (1980-); AROMATICS; Atomic and molecular physics; AZAARENES; AZINES; CARBONYLS; COMPLEXES; CONVERSION; ENERGY CONVERSION; Exact sciences and technology; Fluorescence and phosphorescence; radiationless transitions, quenching (intersystem crossing, internal conversion); HETEROCYCLIC COMPOUNDS; LUMINESCENCE; Molecular properties and interactions with photons; ORGANIC COMPOUNDS; ORGANIC NITROGEN COMPOUNDS; PHENANTHROLINES; PHOTOSENSITIVITY; Physics; PYRIDINES; RHENIUM COMPLEXES; SENSITIVITY; SOLAR ENERGY; SOLAR ENERGY CONVERSION; TRANSITION ELEMENT COMPLEXES; Cationic complex; Ligand effect; Temperature; Nitrogen heterocycle; Organic ligand; Transition metal Carbonyl Complexes; Experimental study; Quantum yield; Charge transfer transition; Emission spectrum; Phosphorescence spectrum; Inorganic compound; Lifetime; Electrochemical properties; Rhenium Carbonyl Complexes; Visible radiation; Visible spectrum
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/ic00346a033

The room- and low-temperature luminescences of ReL(CO){sub 3}X where L = 2,2{prime}-bipyridine, 1,10-phenanthroline, or 5-phenyl-1,10-phenanthroline and X = substituted pyridine or quinoline were studied. Relatively small but useful variations in the state energies can be effected by altering the Hammett {sigma} values of substituents on the pyridines. All complexes exhibit metal to ligand charge-transfer (MLCT) phosphorescences at room temperature. However, by choice of suitable ligands, the emissions can be switched to ligand-localized phosphoresecence on cooling to 77 K. This behavior is explained on the basis of the proximity of the lowest MLCT and {pi}-{pi}{sup *} triplet states and the changes in energy of the MLCT state as a function of temperature. At room temperature the MLCT state can equilibrate to an energy that is lower than that of {sup 3}{pi}-{pi}{sup *} state and give MLCT luminescence. In rigid low-temperature media, however, the MLCT state cannot relax during the excited-state decay and emission is from the lower energy {sup 3}{pi}-{pi}{sup *} state. At room temperature, lifetimes are predominantly affected by alterations in the nonradiative rate constant, as described by the energy-gap law. From {sigma} values of the substituents, both state energies and lifetimes can be predicted before synthesis. The design of new luminescent complexes is discussed. 25 refs., 6 figs., 2 tabs.