Li et al. research the influence of the chloro substituent position on the triplet reactivity of benzophenone derivatives. The 3-chlorobenzophenone (3-Cl-BP), 4-chlorobenzophenone (4-Cl-BP), and 4,4′-dichlorobenzophenone (4,4′-dichloro-BP) triplets exhibit similar hydrogen abstraction ability as has been found previously for the parent BP triplet. In IPA, the 3-Cl-DPK, 4-Cl-DPK, and 4,4′-dichloro-DPK radicals were observed and reacted with DMK radical, most likely at the para-position to form a para-LAT. In a MeCN: H2O/1:1 aqueous solvent, these DPK radicals were also observed but with a slower formation rate. All of these results indicate that the 2-chloro substituent reduces the hydrogen abstraction ability of the substituted BP triplet, not as may be expected that an electron-withdrawing group could increase its photoreduction activity[1].
