To shed light on the reaction mechanism, a control experiment was carried out by additional incorporated stoichiometric radical scavenger 2,2,6,6-tetramethylpiperidinyloxyl (TEMPO) into the reaction system of dihydroquinazolinone 2a with α-trifluoromethyl styrene 3a. As exhibited in Scheme 5A, the model reaction was completely compressed without any production of the desired gem-difluoroallylation product 4aa. By contrast, the cyclohexyl radical generated via C-C bond cleavage of 2a was trapped by TEMPO and a TEMPO-adduct 6 was isolated in 25% yield. Additionally, for the model reaction of 2a and 3a, aside from the desired gem-difluoroalkene 4aa, Scheme 5. Mechanistic Study and Proposed Mechanism. methylquinazolinone 7 was also obtained in 95% yield as the concomitant side product. A radical clock experiment was carried out with cyclopropyl methyl-substituted dihydroquinazolinone 2s as substrate. Under the standard conditions, the ringopening product 4ta was achieved in 50% yield, which suggested the generation of alkyl radical in this transformation. As per these results and previous reports, 19-20 we proposed a plausible reaction mechanism. As illustrated in Scheme 5B, photocatalyst was first excited by visible light to generate a highly oxidizing species 4CzIPN*, which readily oxidized dihydroquinazolinone 2 via a single electron transfer (SET) to afford a radical cation intermediate Int-1 with concomitant generation of the reduced-state 4CzIPN. Driven by gaining aromatic stabilization energy through aromaticity restoration, C-C cleavage of prearomatic dihydroquinazolinone 2 occurred to deliver alkyl radical Int-2 and methylquinazolinone 7. Radical addition of Int-2 onto α-trifluoromethyl alkenes 3 then happened to forge α-CF3 alkyl radical Int-3, which was smoothly reduced to α-CF3 carbanion Int-4 by reduced-state 4CzIPN. Finally, α-CF3 carbanion Int-4 smoothly proceeded β-fluoride elimination to arrive at the gem-difluoroalkenes 4. Alternatively, in the presence of a strong electron-withdrawing group to stabilize carbanion Int-4, direct protonation prevailed over the defluorinative process to yield trifluoromethylated products 5.