A copper(I) coordination polymer, [Cu2I2L2] (CP 1), shows luminescence mechanochromism with a color change from greenish-blue to yellow upon the application of pressure. Powder X-ray diffraction and Raman studies reveal' that the changes iri the bond lengths in crystalline CP 1 are the main cause of luminescence mechanochromism. The luminescence mechanochromic process of CP 1 preserves its crystallinity with a small lattice distortion, despite very high pressure, and it is a non-phase-transition process. After the addition of several drops of acetonitrile to the ground and compressed samples, the original greenish-blue emissive and crystalline states are restored. Therefore, the luminescence color conversion processes are fully reversible.