Using our optimised conditions, we evaluated various substrates. Both electron-donating and electron-deficient aromatic compounds (Fig. ) revealed the promising photocatalytic activity of Sc(OTf)3 in most cases. Toluene (1a) yielded 80% benzoic acid (2a) and p-chlorotoluene (1b) (Eox = +2.43 V vs SEC ) underwent even complete conversion to its respective carboxylic acid 2b. As anticipated, the electron-deficient 4-(trifluoromethyl)toluene (1c), with the highest oxidation potential (Eox = +2.61 V vs SEC ), displayed considerable resistance to oxidation, resulting in trace product formation. Conversely, the less electron-deficient ester group-containing derivative 1d (Eox = +2.45 V vs SCE ) was effectively oxidised. Unexpectedly, 4-methylanisole 1e (Eox = +1.51 V vs SEC ), despite being the most electron-rich substrate, gave only a 4% yield. This could be attributed to the back-electron transfer (BET) process during the oxidation of 1e. Biphenyl 3 (Eox = +1.95 V vs SEC 34 ) underwent efficient oxidation, providing a complete yield of benzoic acid (2a). Oxidation of p-xylene (1f) afforded a mixture of 4-methylbenzoic acid (2f) (67%) and terephthalic acid (2g) (33%) after 24 h of irradiation. Ethylbenzene derivatives 4a-c provided reasonable yields of benzoic acid derivatives according to the electronic effect, although 4-ethyltoluene (4d) was oxidised to a mixture of 4-acetylbenzoic acid (2h) and 2f. By contrast, cumene (5) gave a poor yield of benzoic acid upon oxidation. Diphenylmethane (6) was transformed into a mixture of the corresponding ketone 7 and benzoic acid (2a). 9H-fluorene (8) was converted into fluorenone (9) as a sole product with excellent yield, while stilbene (10) yielded benzoic acid via oxidative C=C cleavage. Further investigation of the oxidation of various primary and secondary aryl alcohols, as depicted in Fig. , revealed that all the tested primary benzyl alcohols, including electron-rich and highly electrondeficient ones 11a-d and o-chlorobenzyl alcohol (11e), were oxidised to the corresponding benzoic acids 2 in quantitative yields. (13c), as anticipated. Surprisingly, the oxidation of 1-phenylethanol (12a) resulted in a low conversion to the corresponding ketone 13a, for a yield of only 23%. A mixture of benzophenone (15) and benzoic acid was obtained following the oxidation of diphenylmethanol (14). By contrast, cinnamyl alcohol (16) underwent a C=C bond cleavage during oxidation to generate a quantitative yield of benzoic acid. Notably, 4-methoxybenzyl methyl ether (17) yielded benzoic acid and not the corresponding ester. The optimised conditions were subsequently used at a preparative scale, with 1 mmol of the selected substrates (see Fig. ) to confirm the practicality and effectiveness of our aerobic photocatalytic oxidation approach employing Sc(OTf)3 (see Supplementary Section S3 for details). The reaction progression was monitored using 1 H NMR analysis and the time was optimised to achieve the maximal conversion of reactants to products. Interestingly, p-xylene (1f), a substrate with two potential oxidation sites, was oxidised chemoselectively to 2f at the preparative scale after appropriately adjusting the reaction time. b Isolated yield (in green); experiments were performed at a 1 mmol scale (see Supplementary Section S3 for details). c Only 2f as the sole product. d 48 h. e 59% of 13b and 16% of 2b, 24 h.