Charge–transfer excitation of electron donor–acceptor complexes of arylcyclopropanes

Abstract

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