True quantum yields and adsorption constants as tools for a mechanistic study of the TiO2-sensitized photooxidation of benzylic derivatives

摘要: Abstract The quantum yields (Φ) of the colloidal TiO2-sensitized photooxidation 4- (1) and 3-methoxybenzyl alcohol (2) together with 4-methoxybenzyltrimethyl- (3) 4-methoxybenzyltriisopropylsilane (4) were determined in CH3CN, presence HClO4 for 3 4. true (Φ0) 1, 2 3, obtained from a Langmuir–Hinshelwood isotherm treatment Φ at different substrate concentrations, are linearly correlated IA−1/2, where IA is light intensity. According to previously suggested mechanisms alcohols silanes, kinetic scheme that justifies this correlation suggested. It shown ratio slopes (from Φ0 versus IA−1/2 plots) 1 equal 0 /Φ any IA; depends on rate constants scheme, case principally electron transfer constant, ket. On contrary, 4 kp, cation radical desilylation confirming steric hindrance nucleophylic assistance CSi fragmentation by bulky isopropyl group SiR3 moiety. Differently Φ0, adsorption semiconductor under irradiation (KD, above treatment) independent IA. Moreover, as K D =K , structural modifications within two silanes should be far enough away site. For all substrates, (the dark constant) five times greater than KD, showing change does not depend structure but result experimental conditions.