Semiconductor-based　photoredox　catalysis　brings　an　innovative　strategy　for　sustainable　organic　transformation　(e.g.,　C-C/C-X　bond　formation),　via　radical　coupling　under　mild　conditions.　However,　since　semiconductors　interact　with　photogenerated　radicals　unselectively,　the　precise　control　of　selectivity　for　such　organic　synthesis　by　steering　radical　conversion　is　extremely　challenging.　Here,　by　the　judicious　design　of　a　structurally　well-defined　and　atomically　dispersed　cocatalyst　over　semiconductor　quantum　dots,　we　demonstrate　the　precise　selectivity　switch　on　high-performance　selective　heterogeneous　coupling　photosynthesis　of　a　C-C　bond　or　a　C-　N　bond　along　with　hydrogen　production　over　the　Ni-oxo　cluster　and　single　Pd　atom-decorated　CdS　quantum　dots　crafted　onto　the　SiO2　support.　Mechanistic　studies　unveil　that　the　Ph(center　dot　CH)NH2　and　PhCH2NH2　center　dot+　act　as　dominant　radical　intermediates　for　such　divergent　organic　synthesis　of　C-C　coupled　vicinal　diamines　and　C-N　coupled　imines,　as　respectively　enabled　by　Ni-oxo　clusters　assisted　radical-radical　coupling　and　single　Pd　atom-assisted　radical　addition-elimination.　This　work　overcomes　the　pervasive　difficulties　of　selectivity　regulation　in　semiconductor-based　photochemical　synthesis,　highlighting　a　vista　of　utilizing　atomically　dispersed　cocatalysts　as　active　sites　to　maneuver　unselective　radical　conversion　by　engineering　quantum　dots　toward　selective　heterogeneous　photosynthesis.