The reduction of six spirocompounds in the absence and presence of polymethylmethacrylate (PMMA) matrix was investigated by in situ spectrochemical measurements. The effect of polymer concentration and chemical structure of spirocompounds on the electrochromism in solution was investigated and an advantage of the presence of the PMMA matrix for two spirooxazine compounds in the bleaching process was reported. The vertical ionization potentials obtained with semiempirical quantum mechanical calculations and those obtained from lambda(max) of the sample solutions in PMMA proved to be consistent with oxidation potentials obtained from cyclic voltametry experiments. This correlation can be explained by the stability of compounds br the PMMA matrix. Copyright (C) 1999 John Wiley & Sons, Ltd.