Square planar platinum complexes have attracted a great deal of interest as phosphorescent chromophores for potential application in many areas, such as sensors, photocatalysts, OLEDs, and photovoltaic devices. For example, platinum [1,3-di(pyrid-2-yl)benzene] chloride (Pt-1) is reported to have a high quantum efficiency over 0.60 and a short radiative lifetime around microsecond. In this presentation, we will discuss our studies on the family of Pt-1. Novel platinum chloride complexes were designed, synthesized, and characterized. The emission color of platinum complexes can be tuned over a large range i.e. blue, green, red, and near infra-red, by varying the functional groups of platinum complexes, thus giving prospects to full-color display. Design, synthesis, photo-physics, electrochemistry and electroluminescent properties of these novel platinum complexes will be discussed. As supported by the spectral analysis of some Pt complexes, small Huang-Rhys factor and high extinction coefficient of triplet transitions provide a strong indication of strong mixing of 1MLCT character into the lowest exited state for this class of platinum complexes.