The Journal of
Physical Chemistry
0 Copyright, 1982, by the American Chemical Society
V O L U M E 86, N U M B E R 14
JULY 8,
1982
LETTERS Photoperoxidation of Unsaturated Organic Molecules. 22. Tetraphenylc yclopentadienone B. Stevens" and K. L. Marsh Department of Chemistry, University of South Florida, Tampa, Florida 33620 (Received: February 4, 1982; In Final Form: May 13, 1982)
Although tetraphenylcyclopentadienone(TPC) both reacts with and quenches O2('Ag)with moderate efficiency, it exhibits no detectable self-sensitized photoperoxidation in hydrocarbon solvents. An analysis of the coronene-sensitized photoperoxidation of TPC as a function of TPC and dissolved-oxygen concentrations in benzene shows that TPC quenching of the coronene triplet state does not inhibit the reaction, indicating that the TPC triplet state produced must generate O2(.'Ag)with unit efficiency; accordingly the failure of TPC to act as an OZ(lAg) sensitizer is attributed to a negligible intersystem crossing yield, and energy transfer to the TPC triplet state must be excluded as a possible OZ('Ag)quenching process. However, the rate constant k~ = (2.6 0.3) X los M-l s-l for 02('Ag) quenching by TPC in benzene increases by a factor of
