Next, we tested the effect of TFA in this photocatalytic fluorination reaction, since it promoted fluorination of 1a (Table , entry 11). Adding 2.0 eq. TFA at the start of the fluorination reaction of 1c, promoted the reaction only to 45% yield of 2c and 4.0 eq. TFA gave 2c in a worse (24%) yield. Although TFA was a superior promotor for 1a's fluorination it was an inferior promoter for 1c's fluorination. The on-line NMR irradiation kinetic experiment (Scheme 6) revealed a long induction period (9.2 h) where scarcely any product is formed (Scheme 6, A). In the presence of 1.0 eq. of H-TEDA(BF 4 ) 2 , the induction period shortened from 9.2 h to 1.4 h (Scheme 6, B). To put in perspective, after 9.2 h of in situ illumination, only 5 mM of product was formed in the standard reaction whereas 16 mM of product was generated by addition of 1.0 eq. H-TEDA(BF 4 ) 2 in the beginning of the reaction. Overall, by addition of 1.0 eq. of H-TEDA(BF 4 ) 2 the induction phase was shortened, and product formation was increased (Scheme 6, C). Another substrate from the same study was 4-phenylbutyl acetate (1b). The key difference from 1a and 1c is that 1b does not contain any attached (benzoyl) photosensitizer, thus eliminating the possibility of background self-fluorination. Substrate 1b was reported to afford only 19% yield of 2b when treated with 1 mol% photocatalyst (MFB) under 400 nm irradiation