Effect of Topologically Controlled Coulombic Interactions on the Dynamic Behavior of Photoexcited Nitrophenyl Alkyl Ethers in the Presence of Tertiary Amines with Limited Motion Freedom

Time-resolved electronic absorption spectroscopy has been successfully applied to clarify the mechanism of the "abnormal" photochemical cleavage of 4-nitrophenyl piperidinoaikyl ethers induced by controlled Coulombic disturbance of the "normal" electronic distribution of the radical anion intermediate. Thus, photolysis of 1-piperidino-2-(2-methoxy-4-nitrophenoxy)ethane (a system with an amine with limited freedom of motion) in acetonitrile leads to C-O bond photocleavage in a relatively slow process (k ≈ 4 × 105 s-1) from intermediate species that show radical-ion pair behavior. Systems with higher freedom of motion of the amine moiety, such as 1-piperidino-5-(2-methoxy-4-nitrophenoxy)pentane or 4-nitroveratrole 4- triethylamine, show the intermediate radicalion pairs mainly evolving to reduction products, probably a result of intermediates with geometries not allowed for the system with limited freedom of motion of the amine.