title: 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.
authors.affiliation: Department of Chemistry, National Tsing Hua University, Hsinchu 300, Taiwan.
authors.forename: Fang-Chi
authors.initials: FC
authors.lastname: Hsu
authors.forename: Yung-Liang
authors.initials: YL
authors.lastname: Tung
authors.forename: Yun
authors.initials: Y
authors.lastname: Chi
authors.forename: Cheng-Chih
authors.initials: CC
authors.lastname: Hsu
authors.forename: Yi-Ming
authors.initials: YM
authors.lastname: Cheng
authors.forename: Mei-Lin
authors.initials: ML
authors.lastname: Ho
authors.forename: Pi-Tai
authors.initials: PT
authors.lastname: Chou
authors.forename: Shie-Ming
authors.initials: SM
authors.lastname: Peng
authors.forename: Arthur J
authors.initials: AJ
authors.lastname: Carty