Hydrogen isotope effects on the excited-state decay properties of polynuclear metal carbonyl hydrides. Emission properties of H/sub 4/Re/sub 4/(CO)/sub 12/ and (n-Bu/sub 4/N)/sub 2/(H/sub 6/Re/sub 4/(CO)/sub 12/)
The two pairs of complexes H/sub 4/Re/sub 4/(CO)/sub 12/,D/sub 4/Re/sub 4/(CO)/sub 12/ and (n-Bu/sub 4/N)/sub 2/(H/sub 6/Re/sub 4/(CO)/sub 12/),(n-Bu/sub 4/N)/sub 2/(D/sub 6/Re/sub 4/(CO)/sub 12/) have been compared with respect to excited-state decay properties. The H/sub 4/Re/sub 4/(CO)/sub 12/ complex exhibits emission from the lowest excited state at 298 K in hydrocarbon solution or as a solid and also at 77 K in glassy hydrocarbon solution or as a pure solid. The emission maximum is between 13700 and 14600 cm/sup -1/ depending on solvent conditions, and the lifetimes range from < 0.02 ..mu..s at 298 K in 3-methylpentane solution (PHI approx. = 0.003) to 16 ..mu..s at 77 K in 3-methylpentane glass (PHI = 0.25). The effect of replacing /sup 1/H by /sup 2/H is to lengthen emission lifetime by 20 to 30% with an equal percent increase in emission quantum yield. The lowest (emissive) excited state can be rapidly quenched by anthracene (triplet energy approx. = 42 kcal/mol) but not by trans-stilbene (triplet energy approx. = 50 kcal/mol), consistent with the high-energy onset (approx. 46 kcal/mol) of the structureless emission spectrum of H/sub 4/Re/sub 4/(CO)/sub 12/ attributable to a lowest-lying triplet excited state associated with a Re/sub 4/ localized electronic transition. (n-Bu/sub 4/N)/sub 2/(H/sub 6/Re/sub 4/(CO)/sub 12/) does not detectably emit in solution or as the solid at 298 K, but emission is detectable at 77 K from the solid or glassy solutions of the salt. The emission is at approx. 18000 cm/sup -1/ with a lifetime of approx.2 ..mu..s and a quantum yield of approx. 0.01. The effect of /sup 1/H replacement by /sup 2/H is to increase lifetime and quantum yield by approx. 50% depending on the medium. Under a given set of conditions for either H/sub 4/Re/sub 4/(CO)/sub 12/ or (H/sub 6/Re/sub 4/(CO)/sub 12/)/sup 2 -/, the effect of replacing /sup 1/H by /sup 2/H is to lower the rate constant for nonradiative decay; there is no effect on the radiative decay constant. 4 figures, 2 tables.
- Research Organization:
- Massachusetts Inst. of Tech., Cambridge
- OSTI ID:
- 6341956
- Journal Information:
- J. Am. Chem. Soc.; (United States), Vol. 103:9
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
DEUTERIUM
ISOTOPE EFFECTS
RHENIUM COMPLEXES
EXCITED STATES
ABSORPTION SPECTRA
ANTHRACENE
CARBONYLS
DECAY
ELECTRONIC STRUCTURE
EMISSION SPECTRA
EXPERIMENTAL DATA
LOW TEMPERATURE
MEDIUM TEMPERATURE
RHENIUM HYDRIDES
AROMATICS
COMPLEXES
CONDENSED AROMATICS
DATA
ENERGY LEVELS
HYDRIDES
HYDROCARBONS
HYDROGEN COMPOUNDS
HYDROGEN ISOTOPES
INFORMATION
ISOTOPES
LIGHT NUCLEI
NUCLEI
NUMERICAL DATA
ODD-ODD NUCLEI
ORGANIC COMPOUNDS
RHENIUM COMPOUNDS
SPECTRA
STABLE ISOTOPES
TRANSITION ELEMENT COMPLEXES
TRANSITION ELEMENT COMPOUNDS
400202* - Isotope Effects
Isotope Exchange
& Isotope Separation