T. Gannon et Wg. Mcgimpsey, 2-LASER-SENSITIZED DECOMPOSITION OF CARBON-TETRACHLORIDE - PHOTOACID GENERATION, Journal of organic chemistry, 58(21), 1993, pp. 5639-5642
Laser flash photolysis (308 mn) of 2-acetylnaphthalene (ATN) in carbon
tetrachloride (CCl4) solution yielded the ATN triplet, T1, state (T-T
absorption: lambda(max) 430 nm). Excitation of T1 to an upper triplet
state, T(n), with a 445-nm pulsed dye laser (ca. 1 mus after the 308-
nm pulse) resulted in extensive permanent bleaching of the T-T absorpt
ion monitored at 430 nm. The bleaching quantum yield was determined by
Aberchrome 540 actinometry, PHI(Bleach) = 0.03 +/- 0.006. While addit
ion of 1 --> 3 M benzene did not effect the transient behavior at 430
nm, the extent of bleaching at 490 nm decreased with increasing benzen
e concentration, indicating the production of a new transient species
concurrent with triplet bleaching. Dependence of the extent of bleachi
ng on benzene concentration and the wavelength of this new absorption
supports its assignment to the chlorine atom-benzene pi-complex, confi
rming that sensitized CCl4 decomposition occurs from the ATN triplet m
anifold, likely via energy transfer. One- and two-laser photolysis of
ATN in 50-50 CCl4/methanol (MeOH) resulted in transient behavior simil
ar to that observed in pure CCl4, but product analysis indicated produ
ction of acid (not observed in pure CCl4). The quantum yield for acid
production under one-laser conditions was PHI(Acid) (one-laser, from g
round state) = 0.0044 +/- 0.0006. Two-laser irradiation resulted in a
ca. 15-fold increase in the amount of acid produced. From the value of
PHI(Bleach) and the ratio of moles triplet bleached to moles acid gen
erated, the quantum yield for production of acid from the triplet stat
e was calculated: PHI(Acid) (two-laser, from triplet state) = 1.9 +/-0
.7.