CHARGE-TRANSFER EXCITATION OF ELECTRON DONOR-ACCEPTOR COMPLEXES OF ARYLCYCLOPROPANES

Electron-transfer (ET) reactions of mono- and di-arylcyclopropanes 1 a nd 2 have been investigated by employing charge-transfer (CT) excitati on of their electron donor-acceptor (EDA) complexes with tetracyanoeth ylene (TCNE) or p-chloranil (CA), For the TCNE complexes, no reaction is observed following photoexcitation within their CT bands, Picosecon d absorption spectroscopic experiments with phenylcyclopropane la and 1,1-diphenylcyclopropane 2a reveal that the photogenerated ion radical pairs [1a(.+), TCNE(.-)] and [2a(.+), TCNE(.-)] are too short-lived t o undergo chemical reaction, For the CA complexes, net chemical change is observed in the CT excitation of the 2a-CA complex though the effi ciency is very low, The other arylcyclopropane-CA complexes are found to be unreactive, Factors concerned with the reactivity of 1 and 2 upo n their CT-excitation are discussed.