Experimental data reveal that the incorporation of carbonyl groups into polymer matrix can significantly enhance singlet oxygen (O-1(2)) generation and suppress production of other reactive oxygen species. Excitonic processes investigated by phosphorescence spectro scopy reveal enhanced triplet-exciton generation in the modified g-C3N4, which facilitate O-1(2) generation through an energy transfer process. Benefiting from this, the modified g-C3N4 shows excellent conversion and selectivity in organic synthesis.