Moreover, photocatalytic methodologies for direct C-H cyanation are limited and still require further exploration. We first used diphenyl ether (18a) (Eox = 1.88 V, vs. SCE) as a benchmark substrate and performed the cyanation using TMSCN as a nucleophilic cyanating agent (12 equiv.) in oxygen-saturated MeCN under blue light irradiation (400 nm) for 24 h. Our preliminary investigations (Fig. , entry 1) showed that a mixture of 4-phenoxybenzonitrile (19a) and 2-phenoxybenzonitrile (19b) could be obtained in a good yield of 74%, with notable regioselectivity towards the para-substituted isomer. Control experiments demonstrated that the cyanation of 18a ceased in the absence of light or Sc(OTf)3, or under anaerobic conditions (entries 2-5). Raising the wavelength of the irradiation source from 400 nm to 450 nm resulted in only trace yields of the desired product (entry 6). For explanation, the cyanating agent TMSCN was used in a significant excess (12 equiv.) to avoid competitive photooxidation reactions (see Supplementary Section S4). Similarly, as was observed for the benzylic oxidations, switching Sc(OTf)3 to Mg(OTf)2, Zn(OTf)2, La(OTf)3, or Ba(OTf)2 resulted in the cessation of cyanation under otherwise identical experimental conditions (see Supplementary Section S4). Switching from MeCN to MeOH or DMSO also completely inhibited the reaction, whereas the reaction in MeNO2 occurred with remarkable conversion. Reaction in dioxane gave small amount of product (Fig. , entries 7-10). Reducing the amount of the Sc(OTf)3 catalyst (2.5 mol%) lowered the yield, whereas doubling the amount (10 mol%) gave a slightly higher yield (entries 11 and 12). Using the optimised conditions, we next investigated the direct cyanation of various arenes, including both electron-rich and electron-poor substrates, as depicted in Fig. . Cyanation of 1,3,5-trimethoxybenzene (18b) and 1,3-dimethoxybenzene (18c) furnished the corresponding carbonitriles 19c and 19d, respectively, as sole products in quantitative yields. Cyanation of 3-chloroanisole (18d) resulted in a mixture of 4-chloro-2-methoxybenzonitrile (19e) and 2-chloro-4-methoxybenzonitrile (19f) in excellent yields, with 3.9:1 regioselectivity. Efficient cyanation of biphenyl (18e) occurred, yielding 4-phenylbenzonitrile (19g). Cyanation of butoxybenzene (18f) led to the formation of 4-butoxybenzonitrile (19h) in a quantitative yield; however, the efficiency of this system in the cyanation of electron-poor substrates was only modest. Cyanation of methyl 2-methoxybenzoate (18g) and 1-methoxy-2-(trifluoromethyl)benzene (18h) gave poor yields of the desired products 19i and 19j, respectively. The highly electron-poor substrates, such as chlorobenzene (18i), methyl benzoate (18j), and trifluorotoluene (18k), did not yield any cyanation products. Subsequent application of the optimised conditions using 1 mmol of the selected substrates 18a and 18d led to cyanation products in good yields, thereby confirming the practicality of our cyanation approach on a preparative scale.