Three different imidazolylidene ligand precursors with methyl groups in 4- and 5-position were synthesized and selected to build a series of nine cyclometalated platinum(II) complexes. Next to the carbene ligands, β-diketonate and bis(pyrazolyl)borate motifs were used as auxiliary ligands. All complexes were fully characterized by standard techniques, five of them also by solid-state structure determinations. All of the synthesized platinum complexes show phosphorescence at room temperature in a PMMA matrix with quantum yields of up to 92% in the green-blue to pure blue area (CIE color coordinates of 0.154; 0.119) of the visible spectrum. Quantum chemical calculations (PBE0/6-311G*) as well as electrochemical experiments provided additional insight into the properties of these compounds.