AbstractCâradical borylation is a significant approach for the construction of carbonïŁżboron bond. Photochemical borylation of aryl halides successfully applied this strategy. However, precise mechanisms, such as the generation of aryl radicals and the role of base additive (TMDAM) and water, remain controversy in these reactions. In this study, photochemical borylation of aryl halides has been researched by density functional theory (DFT) calculations. Indeed, the homolytic cleavage of the CïŁżX bond under irradiation with UVâlight is a key step for generation of aryl radicals. Nevertheless, the generation of aryl radicals may also undergo the process of single electron transfer and the heterolytic carbonïŁżhalogen bond cleavage sequence, and the latter is favorable during the reaction.