The electronic absorption spectrum of the hexamethyl(Dewar benzene) radical cation (1(.+)) is presented for the first time. Partial stabilization of 1(.+) in organic glasses at cryogenic temperatures is explained in terms of matrix rigidity, which can inhibit the isomerization process. Annealing of the matrix leads to fast isomerization of 1(.+) to hexamethylbenzene radical cation (2(.+)) and, at high concentrations of 1, formation of the hexamethylbenzene dimer radical cation can be observed.