The luminescent Cu(I) coordination polymers [Cu2I2(m,m'-bpy)](n) (CuI-m; m,m'-bpy = m,m'-bipyridine; m = 3, 4) were successfully synthesized by the solvent-free thermal reaction of the metal salt CuI with the organic linkers m,m'-bpy. Powder X-ray diffraction analysis revealed that CuI-3 was immediately formed when a mixture of CuI and 3,3'-bpy was ground in a mortar at room temperature (20 degrees C). In contrast, a temperature >120 degrees C was required to synthesize the CuI-4 isomer, probably because of the higher melting point of the 4,4'-bpy linker. Although excess bpy linker was necessary to afford the CuI-m in high yield, the quantitative synthesis, without any purification processes, was successfully achieved by simple heating at 140 degrees C, whereby the excess bpy linker was thermally removed by evaporation. Single crystal X-ray structural analysis indicated that in CuI-3 the dinuclear {Cu2I2} rhombic cores were bridged by 3,3'-bpy linkers. A similar structure was observed for CuI-4; however, the intermolecular pi-pi stacking that was effective in CuI-4 was suppressed in CuI-3 because of the twisted configuration of the two pyridyl rings of the 3,3'-bpy linker. CuI-3 exhibited bright green emission with the maximum (lambda(em)) at 519 nm and a high emission quantum yield (Phi = 0.58) in the solid state at room temperature, in contrast to the weak red emission of CuI-4 (lambda(em) = 653 nm, Phi < 0.01). Emission decay analysis and density functional theory calculations suggested that the CuI-m emissions could be attributed to the delayed fluorescence from the metal-to-ligand charge-transfer excited state effectively mixed with the halide-to-ligand charge-transfer excited state.