Laser studies of radiationless decay mechanisms in Os/sup 2 +///sup 3 +/ polypyridine complexes
The lowest energy excited states in Os(II) polypyridine complexes are of a metal-to-ligand charge transfer (MLCT) type and live for 10 to 40 ..mu..s at 4.2/sup 0/K. The long wavelength absorptions in the visible region of the spectrum in Os(III) polypyridine complexes arise from ligand-to-metal charge transfer (LMCT) transitions and do not produce detectable luminescence. This suggests that these LMCT states are very short lived. Results of picosecond absorption studies on the lifetimes the LMCT states in OsL/sub 3//sup 3 +/ complexes (L = 2,2'-bipyridine(bpy) or 1,10-phenanthroline(phen)) as functions of temperature and isotopic substitution are reported. The LMCT lifetimes at low temperature are contrasted with the low temperature lifetimes of the MLCT states of OsL/sub 3//sup 2 +/ complexes and both are examined from the perspective of a coarse-grained radiationless decay theory developed by Englman, R. and Jortner, J. (Molec. Phys. 1970, 18, 145). The agreement between experiment and theory suggests the following: (1) Englman and Jortner's theory of radiationless decay is useful for inorganic as well as organic systems; (2) mid-frequency (1300 to 1600 cm/sup -1/) vibrations are the important energy accepting modes for radiationless decay of the charge transfer excited states of OsL/sub 3//sup 2 +///sup 3 +/ complexes and; (3) the 10/sup 5/-10/sup 6/ difference in lifetimes between the MLCT states of OsL/sub 3//sup 2 +/ complexes and the LMCT states of OsL/sub 3//sup 3 +/ complexes is largely due to the difference in their energy gaps.
- Research Organization:
- Brookhaven National Lab., Upton, NY (USA)
- DOE Contract Number:
- AC02-76CH00016
- OSTI ID:
- 5146536
- Report Number(s):
- BNL-31632; CONF-8205114-1; ON: DE82019530
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
400201* -- Chemical & Physicochemical Properties
400301 -- Organic Chemistry-- Chemical & Physicochemical Properties-- (-1987)
400500 -- Photochemistry
ABSORPTION SPECTRA
AZINES
BIPYRIDINES
CHARGE TRANSPORT
COMPLEXES
DE-EXCITATION
ELECTROMAGNETIC RADIATION
ENERGY LEVELS
ENERGY TRANSFER
ENERGY-LEVEL TRANSITIONS
EXCITED STATES
HETEROCYCLIC COMPOUNDS
KINETICS
LASER RADIATION
LIGANDS
LOW TEMPERATURE
MEDIUM TEMPERATURE
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
OSMIUM COMPLEXES
PHENANTHROLINES
PYRIDINES
RADIATIONLESS DECAY
RADIATIONS
REACTION KINETICS
SPECTRA
TEMPERATURE DEPENDENCE
TRANSITION ELEMENT COMPLEXES