Liquid substituted 2H-benzotriazole mixtures are prepared by alkylation with concomitant dealkylation, fragmentation and/or realkylation of 2-(2-hydroxy-5-alkylphenyl)-2H-benzotriazoles or of 2-(2-hydroxy-3,5-dialkylphenyl)-2H-benzotriazoles with straight or branched alkenes of 8 to 40 carbon atoms in the presence of an acid catalyst at 100 - 200°C. The liquid mixtures exhibit outstanding efficacy in protecting organic substrates from light induced deterioration as well as good resistance to loss by volatilization or exudation during the processing of stabilized compositions at elevated temperatures.