Color change due to phase transition in N-(2,4-dinitrophenyl)-o-anisidine

N-(2,4-dinitrophenyl)-o-anisidine changes its color from orange to red with change in crystal structures. The orange phase transforms irreversibly int o red phase by heating In the present study, we observed the transformation process by atomic force microscopy to make clear the microscopic transitio n mechanism. The observed images revealed that the red phase is resulted by sublimation of molecules from orange crystal by changing its conformation to the red one and re-adherence to the orange surface with epitaxial relati on.