Temperature dependence of the lifetime of excited benzyl and other arymethyl radicals

Journal Article · Wed Aug 06 04:00:00 EDT 1986 · J. Am. Chem. Soc.; (United States)

DOI:https://doi.org/10.1021/ja00276a004· OSTI ID:5501859

Miesel, D; Das, P K; Hug, G L; Bhattacharyya, K; Fessenden, R W

The temperature dependence of the fluorescence lifetime of benzyl, benzyl-d/sub 7/, ..cap alpha..-methylbenzyl, and triphenylmethyl radicals has been studied in 2-methyltetrahydroduran from 77 to 300 K. Temperature independent and unusual temperature dependent relaxation pathways are observed for the excited states of all four radicals. Activation energies for the temperature-dependent relaxation process are approx.1400 cm/sup -1/ for all these radicals, and frequency factors are in the range of (2-20) x 10/sup 11/ s/sup -1/. For Ph/sub 3/C radicals, the temperature-dependent process leads to observable photochemistry. However, no photochemistry is observed to result from the thermally activated relaxation of benzyl radicals. Possible pathways of these nonradiative decay processes are discussed and contrasted with the weak temperature dependence for the relaxation of diphenylmethyl radicals. It is proposed that the temperature-dependent route for the radiationless decay of benzyl radicals results from differential vibronic mixing of the two excited states, the 1/sup 2/A/sub 2/ and 2/sup 2/B/sub 2/ states. Most efficient in that mixing seems to be C-C stretching vibrational modes.

• Research Organization: Argonne National Lab., IL
• DOE Contract Number: W-31109-ENG-38; AC02-76ER00038
• OSTI ID: 5501859
• Journal Information: J. Am. Chem. Soc.; (United States), Journal Name: J. Am. Chem. Soc.; (United States) Vol. 108:16; ISSN JACSA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400500* -- Photochemistry
ACTIVATION ENERGY
ALKYL RADICALS
ARYL RADICALS
BENZYL RADICALS
CHEMICAL REACTIONS
CHEMISTRY
DATA
DE-EXCITATION
ENERGY
ENERGY LEVELS
ENERGY TRANSFER
ENERGY-LEVEL TRANSITIONS
EXCITED STATES
EXPERIMENTAL DATA
FLUORESCENCE
INFORMATION
LIFETIME
LOW TEMPERATURE
LUMINESCENCE
MEDIUM TEMPERATURE
METHYL RADICALS
NUMERICAL DATA
PHOTOCHEMICAL REACTIONS
PHOTOCHEMISTRY
RADIATIONLESS DECAY
RADICALS
TEMPERATURE DEPENDENCE