.PI.-.PI. and .SIGMA.-.PI. Interactions in .ALPHA.,.OMEGA.-Dinaphthyl and -Dianthryl Oligosilanes in Solution Bis(2-phenylbenzoyl) peroxide (2-PhBPO) photodecomposed by 100% O-O bond cleavage to give mainly biphenyl-2, 2'-carbolactone on 313 nm irradiation, however, on 254 nm, th...