Two　copper(I)　iodide　tetramers,　namely,　[μ2-1,3-bis(diphenylphosphanyl)propane-κ2　P:P′]di-μ3-iodido-di-μ2-iodido-[1-(pyridin-3-yl)ethan-1-one-κN]tetracopper(I)　dichloromethane　disolvate,　[Cu4I4(C6H7NO)2(C27H26P2)2]·2CH2Cl2　(Cu　L　3　),　and　[μ2-1,3-bis(diphenylphosphanyl)propane-κ2　P:P′]di-μ3-iodido-di-μ2-iodido-[1-(pyridin-4-yl)ethan-1-one-κN]tetracopper(I),　[Cu4I4(C6H7NO)2(C27H26P2)2]　(Cu　L　4),　have　been　synthesized　from　reactions　of　CuI,　1,3-bis(diphenylphosphanyl)propane　(dppp)　and　3-　or　4-acetylpyridine　(3/4-acepy).　The　complexes　were　characterized　by　elemental　analysis,　IR　spectroscopy,　single-crystal　X-ray　diffraction　(XRD),　powder　XRD　and　photoluminescence　spectroscopy.　Both　complexes　possess　a　stair-step　[Cu4I4]　cluster　structure　with　a　crystallographic　inversion　centre　located　in　the　middle　of　a　Cu2I2　ring　(Z′　=　1/2).　The　dppp　ligands　each　adopt　a　bidentate　coordination　mode　that　bridges　two　CuI　centres　on　one　side　of　the　[Cu4I4]　cluster　and　the　acepy　ligands　act　as　terminal　ligands.　The　solid-state　samples　of　similar　complexes　show　highly　efficiency　thermally　activated　delayed　fluorescence　(TADF)　at　room　temperature.　At　ambient　temperature,　both　Cu　L3　and　Cu　L　4　exhibit　photoluminescence,　with　a　maximum　emission　in　the　region　560-580-14;nm　and　with　short　emissive　decay　times,　but　only　phosphorescence　was　observed　at　77-14;K.　The　narrow　gaps　between　the　higher　lying　singlet　state　and　the　triplet　state,　ΔE(S1　-　T1),　also　confirm　the　presence　of　TADF.　Structure　analysis　and　consideration　of　photoluminescence　indicates　that　the　position　of　the　acetyl　group　on　the　heterocyclic　ligand　has　an　obvious　influence　on　the　structural　arrangement,　on　intermolecular　interactions　and　on　the　observed　photophysical　properties.　©　2021　International　Union　of　Crystallography.