Exploring and optimization of Sc(OTf)3-based aerobic photocatalytic oxidation of benzylic substrates Upon the surprising observation of the photocatalytic activity of Sc(OTf)3, we directed our attention towards the aerobic oxidation of toluene (1a; Eox = +2.36 V vs SCE ) as a benchmark. The oxidation was performed with 5 mol% of Sc(OTf)3 (Ered = -1.15 V vs SCE 32 ; i.e. not strong enough in ground state to oxidize 1a) in O2-saturated acetonitrile (MeCN) under blue light irradiation (400 nm LED) for 24 h. Encouragingly, this experiment afforded benzoic acid (2a) as the sole product at an 80% yield (Fig. , entry 1). Under anaerobic conditions, or in the absence of light or Sc(OTf)3, the reaction did not proceed (entries 2-5). This system demonstrated significantly decreased effectiveness with 450 nm LED illumination (Entry 6). An assessment of Lewis acids revealed that Sc(OTf)3 was the optimal selection, probably due to its superior ability to bind strongly with O2 An investigation of catalyst loading (Fig. , entries 7 and 8 and Supplementary Section S2) also revealed that using a smaller amount of Sc(OTf)3, at 2.5 mol%, slightly reduced the yield of benzoic acid (2a), whereas employing 10 mol% of the catalyst notably achieved a full conversion to 2a. Moreover, the time-dependent yield profile showed an almost constant rate of toluene (1a) oxidation with increasing reaction time (Fig. ). Consequently, the plot of turnover frequency (TOF) values over the eaction time (4-20 h) remained stable, signifying maintenance of the photocatalytic activity of Sc(OTf)3 (see Supplementary Section S2).