PHOTOCHEMICAL BEHAVIOR OF STABLE FREE-RADICALS - THE PHOTOCHEMISTRY OF PERCHLORODIPHENYLMETHYL RADICAL

The excitation of perchlorodiphenylmethyl radical (PDM) at 530 nm leads to the lowest excited doublet, D1 (tau = 31 ns), from which emission is observed (PHI = 1 X 10(-3) +/- 0.0003). This state is quenched by electron donors and acceptors at a rate at or close to diffusion control and at much slower rates by oxygen and hydrogen atom donors. Fragmentation of PDM (PHI(d) = 0.06) occurs from a higher excited doublet (D(n), n greater-than-or-equal-to 2) producing intermediates that are trapped by O2, chlorine, or hydrogen donors, yielding products 1-6. Experimental evidence suggests a structure-photoreactivity correlation in the perchlorinated arylmethyl radicals in which the partitioning between photochemical cyclization or fragmentation depends on the twist angle between the appended phenyl rings.