Rate-determining step for decay of triplet biradicals: intersystem crossing vs. chain dynamics

Journal Article · Wed Jun 25 04:00:00 EDT 1986 · J. Am. Chem. Soc.; (United States)

DOI:https://doi.org/10.1021/ja00273a012· OSTI ID:5532904

Zimmt, M B; Doubleday, C Jr; Turro, N J

The temperature and viscosity dependence of the lifetimes of triplet biradicals derived from 2-phenylcycloalkanones have been studied by means of nanosecond transient UV absorption. Arrhenius plots for the temperature range 20 to -90/sup 0/C are strongly curved. In the high-temperature range (ca. -10 to +20/sup 0/C) log A (S/sup -1/) and E/sub a/ (kcal/mol) are ca. 8.0 and 1.0, respectively. In the low-temperature range (-50 to -90/sup 0/C) the values are ca. 10-11 and 3-4, respectively, typical of chain cyclization processes. The biradical lifetimes are strongly affected by solvent viscosity at low temperature but are nearly insensitive to viscosity at room temperature. The data suggest a transition in the rate-determining step for biradical decay from intersystem crossing control at room temperature to chain dynamics control at low temperature. At room temperature and above, the observable biradicals are almost exclusively triplets, but at low temperature one observes the decay of an approximately equilibrium mixture of singlets and triplets.

• Research Organization: Columbia Univ., New York, NY
• OSTI ID: 5532904
• Journal Information: J. Am. Chem. Soc.; (United States), Journal Name: J. Am. Chem. Soc.; (United States) Vol. 108:13; ISSN JACSA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400301* -- Organic Chemistry-- Chemical & Physicochemical Properties-- (-1987)
400500 -- Photochemistry
ARRHENIUS EQUATION
CHEMICAL REACTIONS
DATA
DE-EXCITATION
DECOMPOSITION
ELECTRONIC STRUCTURE
ENERGY TRANSFER
ENERGY-LEVEL TRANSITIONS
EQUATIONS
EXPERIMENTAL DATA
INFORMATION
KETONES
LOW TEMPERATURE
MEDIUM TEMPERATURE
MULTIPLETS
NUMERICAL DATA
ORGANIC COMPOUNDS
PHOTOCHEMICAL REACTIONS
PHOTOLYSIS
PHYSICAL PROPERTIES
RADIATIONLESS DECAY
RADICALS
THERMODYNAMIC PROPERTIES
TRIPLETS