Single-layer　carbon-based　dots　(SCDs)　were　chosen　as　a　model　to　investigate　the　effect　of　the　C-related　dangling　bonds　with　spin　S=1/2　and　functional　groups　on　the　electrochemiluminescent　(ECL)　and　fluorescent　(FL)　properties　of　CDs.　The　C-related　dangling　bonds　and　functional　groups　of　SCDs　were　tuned　by　chemical　reduction　with　NaBH4.　There　have　several　main　findings　via　investigating　the　ECL　and　FL　properties　of　SCDs　before　and　after　the　chemical　reduction.　First,　the　FL　and　ECL　of　CDs　are　highly　dependent　on　their　concentration,　and　luminescent　resonance　energy　transfer　is　observed　in　ECL　studies　when　the　concentration　of　CDs　is　high.　Second,　the　ECL　activity　of　CDs　is　greatly　enhanced　as　the　C-related　dangling　bonds　increase,　proving　that　the　ECL　of　CDs　originates　from　the　C-related　dangling　bonds.　Third,　the　FL　of　CDs　is　the　synthesis　of　the　inner　FL　originated　from　the　contained　isolated　sp(2)　units　and　the　defect　FL　from　the　C-related　dangling　bonds.　The　inner　FL　of　CDs　is　enhanced　greatly　by　removing　the　carboxyl　groups,　while　the　defect　FL　is　increased　slightly　due　to　the　increased　C-related　dangling　bonds.　We　believe　this　study　would　promote　our　understanding　in　the　ECL　and　FL　mechanisms　of　CDs,　advancing　the　applications　of　CDs　based　on　their　ECL　and　FL　properties.