The spectra of the radical cations produced following laser excitation of a range of anthracene derivatives and amines adsorbed on silica gel are reported and their geminate ion-electron recombination kinetics investigated. Silica gel is shown to be a convenient medium in which to study unstable species such as radical ions which are either very short-lived or inaccessible in a solution environment. Triplet-triplet absorption spectra for dialkyl- and dialkoxy-substituted anthracenes adsorbed on silica gel are consistent with solution phase studies. Tn contrast to solution phase studies, radical cations from these molecules are readily observed on silica gel acid are produced via a multiphoton ionization route. The positions of the radical cation absorption spectra, in contrast to both the ground state and triplet-triplet absorption spectra, are a sensitive function of both substituent and substitution patterns. For substitution across the short molecular axis, electron-donating substituents elicit a hypsochromic spectral shift. In contrast, substitution by electron-donating substituents in the 2,3- or 2,6-positions give rise to bathochromic shifts in the radical cation absorption spectra. Also studied are the kinetics of geminate ion-electron recombination, which when compared with measured oxidation potentials demonstrate that charge transfer energetics are not the only factor controlling the observed recombination rates.