Photosensitized dissociation of di-tert-butyl peroxide. Energy transfer to a repulsive excited state

Journal Article · Wed Feb 11 00:00:00 EST 1981 · J. Am. Chem. Soc.; (United States)

DOI:https://doi.org/10.1021/ja00393a024· OSTI ID:6875577

Scaiano, J C; Wubbels, G G

Energy transfer from a variety of aromatic hydrocarbons and ketones to di-tert-butyl peroxide has been examined by using nanosecond laser flash photolysis techniques. Triplet energy transfer to the peroxide leads to its efficient cleavage into two tert-butoxy radicals. Representative rate constants for triplet quenching in benzene at 25/sup 0/C are 7.9 x 10/sup 6/, 3.4 x 10/sup 6/, and 7.0 x 10/sup 4/M/sup -1/s/sup -1/ for p-methoxypropiophenone, benzophenone, and benz(a)anthracene, respectively. The rate of transfer for p-methoxypropiophenone (E/sub T/ = 72.5 kcal/mol) is approximately temperature independent; for lower energy sensitizers ca. 0.17 kcal/mol activation energy is required for each kilocalorie per mole decrease in triplet energy. No evidence indicating exciplex intermediacy was found. A model for energy transfer to a repulsive state of the peroxide is proposed in which no activation energy is required if the sensitizer meets the energy requirements at the 0-0 equilibrium distance. For sensitizers of lower triplet energy, energy transfer to a repulsive state is proposed to occur from a thermally activated ground state having a greater than equilibrium oxygen-oxygen bond length. The same mechanism may apply in other systems where the acceptor lacks low-lying excited states. A few rate constants for the quenching of singlet sensitizers have also been determined by using fluorescence techniques.

• Research Organization: Univ. of Notre Dame, IN
• OSTI ID: 6875577
• Journal Information: J. Am. Chem. Soc.; (United States), Vol. 103:3
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
AROMATICS
ENERGY TRANSFER
KETONES
PEROXIDES
PHOTOLYSIS
BENZOPHENONE
FLUORESCENCE
LASER RADIATION
RADICALS
SCINTILLATION QUENCHING
TRIPLETS
CHEMICAL REACTIONS
DECOMPOSITION
ELECTROMAGNETIC RADIATION
LUMINESCENCE
MULTIPLETS
ORGANIC COMPOUNDS
OXYGEN COMPOUNDS
PHOTOCHEMICAL REACTIONS
RADIATIONS
400500* - Photochemistry