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 cl eavage of 4-nitrophenyl piperidinoalkyl ethers induced by controlled C oulombic disturbance of the ''normal'' electronic distribution of the radical anion intermediate. Thus, photolysis of 1-piperidino-2-(2-meth oxy-4-nitrophenoxy (a system with an amine with limited freedom of mot ion) in acetonitrile leads to C-O bond photocleavage in a relatively s low process (k approximate to 4 x 10(5) s(-1)) from intermediate speci es that show radical-ion pair behavior. Systems with higher freedom of motion of the amine moiety, such as 1-piperidino-5-(2-methoxy-4-nitro phenoxy)pentane or 4-nitroveratrole + triethylamine, show the intermed iate radical-ion 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.