Radical cations of perinaphthocyclopropanes. Conditions for the observation of 1,3-perinaphthadiyl radical cations

gamma -Irradiation of 7,7a-dihydro-6bH-cycloprop[a]acenaphthylene (1) and i ts 7,7-dimethyl derivative (2) in haloalkane glasses at 77 K yields persist ent parent radical cations of these compounds. On visible irradiation, 1(.) is transformed into the radical cation of phenalene, 3(.+), which was als o generated independently from neutral 3. The transformation 1(.+)--> 3(.+) presumably proceeds by opening of the central cyclopropane bond and subseq uent H-shift in the resulting perinaphthadiyl radical cation which is, howe ver, not observed. Surprisingly, the dimethyl derivative, 2(.+), is also tr ansformed into a phenalene radical cation by visible photolysis. In this ca se the mechanism is probably a different one, involving a distonic diyl cat ion obtained by cleavage of a lateral cyclopropane bond. In contrast to the above, the ring opening of the dicyclopropa[a,g]pyracyclene 4 radical cati on proceeds stepwise, and the perinaphthadiyl cation intermediate can be ob served. A second photochemical ring opening yields the radical cation of 2, 7-dihydro-2,2,7,7-tetramethylpyrene that was generated independently from t he neutral precursor. The electronic absorption spectra of all observed radical cations are discu ssed in conjunction with the corresponding photoelectron spectra (where ava ilable) and with quantum chemical calculations.