In　this　work,　six　iridium(III)　complexes　have　been　designed,　synthesized　and　characterized.　The　molecular　structures　of　complex　1　([(pba)2Ir(bpy-2N(CH3)2)]PF6),　2　([(pba)2Ir(bpy-2NH2)]PF6)　and　3　([(pba)2Ir(bpy-2CH3)]PF6)　were　determined　by　single　crystal　X-ray　diffraction.　Upon　addition　of　Hcy　(homocysteine)　to　the　solution　of　complex　1,　a　luminescent　variation　from　orange　red　to　green　was　observed　by　the　naked　eye,　corresponding　to　a　large　blue　shift　from　604　nm　to　498　nm　(~106　nm).　While　the　emission　intensity　of　complex　1　was　almost　no　change　after　addition　of　other　common　amino　acids　including　Cys　(cysteine)　and　GSH　(glutathione).　The　aldehyde　group　of　complex　1　formed　a　new　thiazinane/thiazolidine　ring　with　Hcy/Cys　confirmed　by　1H　NMR　and　high-resolution　mass　spectrometry.　And　the　new　product　1-Hcy　had　a　higher　quantum　yield　than　1-Cys.　Theoretical　calculations　showed　that　the　HOMO　(highest　occupied　molecular　orbital)　of　1-Hcy　was　located　on　the　newly　formed　six-membered　thiazinane　ring,　which　was　different　from　the　HOMO　of　1-Cys.　Compared　with　the　other　iridium(III)　complexes,　we　can　speculate　that　the　large　blue　shift　and　enhancement　of　the　emission　intensity　of　the　complex　1　were　related　to　the　strong　electron　donating　ability　of　the　modified　amino　groups　on　bipyridine　ligand.　This　will　provide　an　idea　for　the　design　of　ratio-based　luminescence　probes　for　Hcy　in　future.　©　2021　Elsevier　B.V.