Design and synthesis of cyclometalated transition metal complexes as functional phosphorescent materials

Abstract

Cyclometalated Ir(III) and Pt(II) compounds are among the most promising phosphorescent emitters for various applications, such as organic light emitting diodes (OLEDs), chemical sensors and bioimaging labels. This family of complexes exhibits high thermal and photo-stability, excellent quantum efficiency, and relatively short lifetime. More importantly, their luminescent properties can be fully tunable by modifying the coordinating ligands. In this thesis, a series of 2-(1,2,3-triazol-4-yl)-pyridine derivatives, referred to as the "click" ligands, are used to build phosphorescent Ir(III) and Pt(II) compounds. The robust and tolerant nature of the copper mediated 1,3-dipolar cycloaddition reactions offers great flexibility in the molecular design. Chapter 1 and Chapter 2 focus on the synthesis of heteroleptic cyclometalated Ir (III) and Pt(II) complexes by utilizing the Cu(I) triazolide intermediates generated in "click" reactions as transmetalating reagents. Ligand synthesis and metalation can be achieved in one pot under mild reaction conditions. For the Ir(III) system, the "click" ligands show switchable coordination modes, between the C, N- and N, N-chelation. These ligands act as C, N, N-bridging units to form unique zwitterionic dinuclear complexes with two cyclometalated Pt(II) units. In Chapter 3, cyclometalated Pt(II) complexes with N, N-chelating "click" ligands are synthesized. Their aggregation-induced solid-state emission is highly responsive to environmental stimuli, such as solvents, heat and mechanical force. This family of compounds represents the first thermotropic Col(h) liquid crystals with only one sidechain. Furthermore, the combined liquid crystalline and mechanochromic properties make them attractive functional materials.