Synthesis and Characterization of Luminescent Cyclometalated Platinum(II) Complexes of 1,3-Bis-Hetero-Azolylbenzenes with Tunable Color for Applications in Organic Light-Emitting Devices through Extension of π Conjugation by Variation of the Heteroatom

A series of luminescent cyclometalated platinum(II) complexes of N&ANDC&ANDN ligands [N&ANDC&ANDN = 2,6-bis(benzoxazol-2-yl)benzene (bzoxb), 2,6-bis(benzothiazol-2-yl)benzene (bzthb), and 2,6-bis(N-alkylnaphthoimidazol-2-yl)benzene (naphimb)] has been synthesized and characterized. Two of the platinum(II) complexes have been structurally characterized by X-ray crystallography. Their electrochemical, electronic absorption, and luminescence properties have been investigated. In dichloromethane solution at room temperature, the cyclometalated N&ANDC&ANDN platinum(II) complexes exhibited rich luminescence with well-resolved vibronic-structured emission bands. The emission energies of the complexes are found to be closely related to the electronic properties of the N&ANDC&ANDN ligands. By varying the electronic properties of the cyclometalated ligands, a fine-tuning of the emission energies can be achieved, as supported by computational studies. Multilayer organic light-emitting devices have been prepared by utilizing two of these platinum(II) complexes as phosphorescent dopants, in which a saturated yellow emission with Commission International de I'Eclairage coordinates of (0.50, 0.49) was achieved.