En Route to the Formation of High-Efficiency, Osmium(II)-Based Phosphorescent Materials

Abstract

Triosmium cluster complexes [Os3(CO)8(fppz)2] (2a) and [Os3(CO)8(fptz)2] (2b) bearing two 2-pyridyl azolate ligands were synthesized in an attempt to establish the reaction mechanism that gives rise to the blue-emitting phosphorescent complexes [Os(CO)2(fppz)2] (1a) and [Os(CO)2(fptz)2] (1b) [(fppz)H = 3-(trifluoromethyl)-5-(2-pyridyl)pyrazole; (fptz)H = 3-(trifluoromethyl)-5-(2-pyridyl)triazole]. X-ray structural analysis of 2b showed an open triangular metal framework incorporating multisite-coordinated 2-pyridyltriazolate ligands. Treatment of 2 with the respective 2-pyridylazolate ligand led to the formation of blue-emitting complex 1b, confirming their intermediacy, while the reaction of 2b with phosphine ligand PPh2Me afforded two hitherto novel hydride complexes 3 and 4, for which the reversible interconversion was clearly established at higher temperatures (> 180 degrees C). The single-crystal X-ray diffraction analyses of 3 and 4 confirmed their monometallic and isomeric nature, together with the coordination of two phosphine ligands located in the trans-disposition and one CO and one hydride located opposite to the pyridyl triazolate chelate. Subtle differences in photophysical properties were examined for isomers 3 and 4 on the basis of steady state absorption and emission, the relaxation dynamics, and temperature-dependent luminescent studies. The results, in combination with time-dependent density function theory (TDDFT) calculations, provide fundamental insights into the future design and preparation of highly efficient phosphorescent emitters.

Theoretical study on the electronic structures and phosphorescent properties of a series of iridium(III) complexes with the different positional N-substitution in the pyridyl moiety

“…complexes have attracted considerable attention as the emitting layers in organic light-emitting diodes (OLEDs) because of their good color purity, high phosphorescence emission quantum yields, short excited triplet state lifetime, and high photochemical stability [1][2][3][4][5][6][7][8]. Especially, phosphorescent Ir(III) complexes have been extensively investigated due to their good phosphorescent emission properties since the pioneering works were performed by Thompson and coworkers [9][10][11].…”

Organic light‐emitting materials based on iridium(III) complexes bearing phenanthroimidazole ligands

“…Therefore, both singlet and triplet excitons can be harnessed, and then strong electroluminescence with an internal efficiency theoretically approaching to 100% can be achieved. [5][6][7][8] Host materials in phosphorescent organic light-emitting diodes (PhOLEDs) have drawn intensive attention owing to their capability to prevent triplet-triplet annihilation and concentration quenching effect. [9][10][11] The Ir(III) complexes reported generally contain two cyclometalated ligands and a bidentate, monoanionic ancillary ligand, or with three cyclometalated ligands.…”

“…The strong spin–orbit coupling induced by a heavy‐metal ion promotes an efficient intersystem crossing (ISC) between the singlet and the triplet excited state manifold. Therefore, both singlet and triplet excitons can be harnessed, and then strong electroluminescence with an internal efficiency theoretically approaching to 100% can be achieved . Host materials in phosphorescent organic light‐emitting diodes (PhOLEDs) have drawn intensive attention owing to their capability to prevent triplet–triplet annihilation and concentration quenching effect .…”

Synthesis of a highly phosphorescent emitting iridium(III) complex and its application in OLEDs

“…The strong spinorbit coupling induced by a heavy-metal ion, such as Os, Ir, and Pt promotes an efficient intersystem crossing (ISC) between the singlet and the triplet excited state manifold. Therefore, both singlet and triplet excitons can be harnessed and then strong electroluminescence with an internal efficiency theoretically approaching to 100% can be achieved [6][7][8][9][10]. In particular, cyclometalated iridium(III) complexes show high phosphorescent efficiencies and relatively short lifetimes, and thus behave as one of the most promising class of phosphorescent dyes in OLEDs.…”