A new class of brightly phosphorescent Pt(II) compounds that contain an N<^>C-chelate phenyl-1,2,3-triazolyl ligand (ptrz) and an N<^>C-chelate pyridyl-1,2,4-triazolyl ligand (pytrz) in the central core is achieved. The impact of various substituent groups on phosphorescence of this class of molecules is examined. Crystal structural analyses revealed that this class of compounds has a great tendency to form stacked dimers-one of which is persistent even in the gas phase-leading to excimer emission. The introduction of bulky substituents, such as diphenyl amino (NPh2) or trityl (CPh3), is found to greatly diminish the excimer emission. Using this approach, several highly efficient blue and green phosphorescent Pt(II) compounds with. em at approximate to 450-460 nm and Phi(p) approximate to 0.70 to 1.00 are obtained. These molecules are highly robust with exceptionally high thermal stability. Bright bluish-green electrophosphorescent devices with external quantum efficiencies as high as 16.7% are fabricated.