Photoprocesses in diphenylpolyenes. 2. Excited-state interactions with stable free radicals

Journal Article · Sat Jan 01 04:00:00 EST 1983 · J. Am. Chem. Soc.; (United States)

DOI:https://doi.org/10.1021/ja00358a002· OSTI ID:7050928

Chattopadhyay, S K; Das, P K; Hug, G L

Singlet and triplet quenching by two stable free radicals, viz., di-tert-butylnitroxy (DTBN) and 4-hydroxy-2,2,6,6-tetramethylpiperidinyl-1-oxy (HTMP), have been studied with three all-trans ..cap alpha..,..cap omega..-diphenylpolyenes, Ph(t-C=C)/sub n/Ph, n = 2-4, as excited-state substrates in different solvents. Data are presented for fluorescence quenching rate constants (0.8-2.1 x 10/sup 10/ M/sup -1/ s/sup -1/ in cyclohexane/methanol), the fraction of singlet quenching events that result in triplet generation (0.06-0.60), and rate constants for triplet quenching (0.18-4.8 x 10/sup 8/ M/sup -1/ s/sup -1/ in solvents ranging from dimethyl sulfoxide to cyclohexane). As with aromatic hydrcarbons, the dependence of triplet quenching rate constants for polyenes on triplet energy (E/sub T) is found to be parabolic; that is, they first decrease systematically on going from trans-stilbene (n = 1) to trans-1,6-diphenyl-1,3,5-hexatriene (n=3) and then increase on going from the latter to trans-1,8-diphenyl-1,3,5,7-octatetraene (n = 4). Possible interactions in terms of charge transfer, energy tranfer, and electron exchange as well as roles of torsional motions and twisted configurations of polyenes in the quenching processes are discussed. 29 references, 5 figures, 4 tables.

• Research Organization: Univ. of Notre Dame, IN
• OSTI ID: 7050928
• Journal Information: J. Am. Chem. Soc.; (United States), Journal Name: J. Am. Chem. Soc.; (United States) Vol. 105:20; ISSN JACSA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400500* -- Photochemistry
ALKANES
CYCLOALKANES
CYCLOHEXANE
ELECTRON TRANSFER
ENERGY LEVELS
ENERGY TRANSFER
EXCITED STATES
FLUORESCENCE
HYDROCARBONS
KINETICS
LUMINESCENCE
METHANE
ORGANIC COMPOUNDS
ORGANIC PHOSPHORUS COMPOUNDS
POLYENES
QUENCHING
RADICALS
REACTION KINETICS