GENERATION AND IDENTIFICATION OF 1,4-PERINAPHTHADIYL RADICAL-CATION -FIRST OBSERVATION OF THE ELECTRONIC ABSORPTION-SPECTRUM OF AN IONIZEDDIRADICAL

gamma-Irradiation of 6b,7,8,8a-tetrahydrocyclobut[a]acenaphthylene (CA N) in haloalkane glasses at 77 K yields a persistent radical cation, C AN(.+), whose electronic absorption spectrum has been obtained. Irradi ation at >640 nm converts this into an isomer which is identical with that formed by ionization of ,4-dihydro-1,4-ethanonaphtho[1,8-de][1,2] diazepine (END) and subsequent irradiation of the radical cation at la mbda > 540 nm. In both cases, further irradiation at 450 nn yields the radical cation of 1,8-divinylnaphthalene (DVN.+) which was identified by ionization of DVN generated in situ by photolysis of CAN. These re lated observations identify the photoisomer of CAN(.+) as 1,4-perinaph thadiyl radical cation (7,8,9,10-tetrahydrocyclohepta[de] naphthalene- 7,10-diylium, CND.+). [GRAPHICS] The molecular and electronic structur es of all observed radical cations, as well as their electronic absorp tion spectra, are discussed on the basis of B3LYP and CASPT2 quantum c hemical calculations and, in the case of CAN(.+) and DVN.+, also by re ference to the photoelectron spectra of the neutral hydrocarbons. The CAN(.+)-->PND.+-->DVN.+ sequence of photoreactions is discussed on the basis of orbital and state correlation diagrams.