Several new square planar platinum(II) complexes based on modified 2-phenylpyridine derivatives as the main ligand and picolinic acid as the auxiliary ligand were synthesized and their photophysical properties, and mechanochromic and liquid crystalline behavior were investigated. It is found that only the Pt–L¹ complexes, in which one flexible long chain is attached to each end of 2-phenylpyridine, display monotropic smectic liquid crystalline behavior. Moreover, mechanochromism has been observed by grinding the solid complexes. It seems that the liquid crystalline and mechanochromic properties of these complexes are relative to the number of flexible alkoxy chains in the cyclometalated ligand.