Blue light photocatalysis of carbazole-based conjugated microporous polymers: Aerobic hydroxylation of phenylboronic acids to phenols

Aerobic hydroxylation of phenylboronic acids to phenols has attracted considerable attention but is exceedingly challenging due to the obstacle in the activation of oxygen (O2). Here, two carbazole-based conjugated microporous polymers (CMPs), namely TCB-CMP and EFC-CMP, were fabricated through polymerization of 1,3,5-tri(9H-carbazole-9-yl)benzene (TCB) and 9,9′-(9,9-diethyl-9H-fluorene-2,7-diyl)bis(9H-carbazole) (EFC), respectively. Gratifyingly, with N,N'-diisopropylethylamine (DIPEA) as the hole (h+) quencher, blue light photocatalysis of both carbazole-based CMPs could execute the aerobic hydroxylation of phenylboronic acids in ethanol (C2H5OH). Importantly, the EFC-CMP imparted superior photocatalytic activity to TCB-CMP due to the favorable reduction of O2 to superoxide anion (O2•–) by electron (e–). Thereby, O2•– conducted the highly selective aerobic hydroxylation of phenylboronic acids. The aerobic hydroxylation of a wide range of phenylboronic acids to corresponding phenols was achieved with high yields. The work further demonstrates the feasibility of taming the oxidation potential of CMPs in producing delicate products like phenols.