Solvent–iodine atom charge transfer absorption in liquid alkanes and cycloalkanes

Abstract

The transient absorptions produced in photolyzed solutions of I₂ in alkanes and cycloalkanes have been investigated by laser flash photolysis, using the frequency-doubled Nd³⁺ line at 530 nm. In most cases, a broad absorption was found, with a poorly-defined maximum in the range 270–350 nm, which disappeared uniformly according to second-order kinetics.

In methylcyclohexane + CCl₄ mixtures, the transient absorption spectrum varies with solvent composition in the manner to be expected if it represents the sum of contributions from each component, in proportion to the concentration. This clearly supports the idea of “contact” charge transfer absorptions rather than charge transfer “complexes”. However in mixtures of perfluoro-n-hexane and n-hexane the transient absorbance is not a linear function of n-hexane concentration, but the changes in the transient absorption spectrum with composition appear largely attributable to the considerable change of dielectric constant from neat alkane to almost neat perfluoroalkane.