Solvatochromism of carbenium–arene EDA (electrondonor–acceptor) complexes and their behaviour on silica

Abstract

AbstractSpectral characteristics of two different types of electron donor–acceptor (EDA) complexes with charged components (arene–carbenium and anion–π acceptor) are presented. The UV–Vis absorption maxima of the charge‐transfer (CT) band (νmax,CT) of the EDA complexes were measured in various solvents and after adsorption on silica. Tropylium, triarylmethylium and diarylmethylium ions in combination with aromatic π donors, e.g. pyrene, acenaphthene and methoxy‐substituted benzene derivatives and also the tetraethylammonium iodide–1,3,5‐trinitrobenzene complex have been investigated by means of a special UV–Vis technique in transparent slurries of silica nanoparticles in 1,2‐dichloroethane. Multiple linear regression analyses of the νmax,CT values of the EDA complexes in various solvents and on silica with the Kamlet–Taft solvent parameters and structure–reactivity terms of the complex components, e.g. the oxidation potential of the arene component or the Hammett substituent constant, σp+, of the arylmethyl component, show their related properties to the solution complexes. The influence of the electron‐pair donating capacity of a solvent on νmax,CT of carbenium/arene complexes was compared with the property of the silica surface in order to link EDA complexes. For the diarylmethyl carbenium ion–pyrene complexes on silica, the presence of a σ‐like structure is discussed. Copyright © 2001 John Wiley & Sons, Ltd.