This　work　aimed　to　develop　organic　photocatalysts　(PCs)　that　could　mediate　organocatalytic　atom　transfer　radical　polymerization　(O-ATRP)　under　visible　light.　Through　the　core-modification　of　known　chromophoric　structures　and　ring-locking　to　reach　a　conjugation　extension,　annulated　N-aryl　benzo[kl]acridines　were　identified　as　effective　visible　light-responsive　photocatalysts.　The　corresponding　selenium-doped　structure　showed　excellent　performance　in　the　O-ATRP　of　methacrylates,　which　could　afford　polymer　products　with　controlled　molecular　weights　and　low　dispersities　under　the　irradiation　of　visible　light　at　a　100　ppm　catalyst　loading.