2-LASER-SENSITIZED DECOMPOSITION OF CARBON-TETRACHLORIDE - PHOTOACID GENERATION

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 absorption monitored at 430 nm. The bleaching quantum yield was determined by Aberchrome 540 actinometry, PHI(Bleach) = 0.03 +/- 0.006. While addition of 1 --> 3 M benzene did not effect the transient behavior at 430 nm, the extent of bleaching at 490 nm decreased with increasing benzene concentration, indicating the production of a new transient species concurrent with triplet bleaching. Dependence of the extent of bleaching on benzene concentration and the wavelength of this new absorption supports its assignment to the chlorine atom-benzene pi-complex, confirming that sensitized CCl4 decomposition occurs from the ATN triplet manifold, likely via energy transfer. One- and two-laser photolysis of ATN in 50-50 CCl4/methanol (MeOH) resulted in transient behavior similar to that observed in pure CCl4, but product analysis indicated production of acid (not observed in pure CCl4). The quantum yield for acid production under one-laser conditions was PHI(Acid) (one-laser, from ground 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 generated, the quantum yield for production of acid from the triplet state was calculated: PHI(Acid) (two-laser, from triplet state) = 1.9 +/-0.7.