Synthesis and Characterization of Metal Complexes Possessing the 5-(2-Pyridyl) Pyrazolate Ligands:  The Observation of Remarkable Osmium-Induced Blue Phosphorescence in Solution at Room Temperature

Abstract

A total of three distinctive main group and transition metal complexes containing the 2-pyridyl pyrazolate (pypz) ligand were prepared, namely, [B(C 6 F 5 ) 2 (pypz)] (1), [Ru(CO) 2 -(pypz) 2 ] (2), and [Os(CO) 2 (pypz) 2 ] (3), where (pypz)H ) 3-trifluoromethyl-5-(2-pyridyl)pyrazole. Single-crystal X-ray diffraction studies were carried out on complexes 2 and 3, revealing octahedral coordination geometry with two CO ligands located at cis dispositions. While the pypz ligand arrangement for complex 2 is in cis-(N py ,N py ) and trans-(N pz ,N pz ), complex 3 reveals a different configuration, cis-(N pz ,N pz ) and trans-(N py ,N py ) (N py for pyridine-N and N pz for pyrazolate donor sites). Similar to that of the in-situ-prepared pypz anion, the boron complex [B(C 6 F 5 ) 2 (pypz)] (1) exhibits a strong emission centered at 380 nm, which is unambiguously assigned to fluorescence derived from the S 1 (ππ*) f S 0 transition. In contrast to the nonluminescent behavior for Ru complex 2, the Os complex 3 displays unique, strong room-temperature phosphorescence, showing vibronic progressions at 430, 457, and 480 nm. The remarkable differences in photophysical properties were rationalized by a combination of π-electron accepting CO ligand, relative pypz orientation, and heavy-atom-enhanced spinorbit coupling effects.

Iridium(I) Pyridyl Azolate Complexes with Saturated Red Metal‐to‐Ligand Charge Transfer Phosphorescence; Fundamental and Potential Applications in Organic Light‐Emitting Diodes

“…The strong absorption bands in the UV region are assigned to the spin-allowed 1 pp* transition of the pyridyl azolate ligands. [14] The lower-lying energy absorption at about 420 nm is broad with some structural features. It seems reasonable to assign this broad absorption feature to the multiple components of the d p !p* (or MLCT) transition on the basis of their positions and relative intensities.…”

New heteroleptic cyclometalated iridium(III) complexes containing 2-(2′,4′-difluorophenyl)-4-methylpyridine for organic light-emitting diode applications

“…The mixing of singlet and triplet excited states by doping phosphorescent dyes into a charge-transporting host as emissive layers greatly enhances the internal phosphorescence quantum efficiency of OLEDs toward 100% [12][13][14]. Adequate modification of the coordinated ligands can tune the emission color from red/green to blue, although blue phosphorescent emitters are more difficult to achieve than red/ green [15][16][17].…”

Synthesis and Photophysical Properties of Rhenium(I)-Alkynyl Molecular Rectangles

“…Luminescence decay measurements were performed with an Edinburgh single-photon counting instrument. The flash photolysis apparatus for the measurement of transient absorption spectra in the nanosecond time domain has been described elsewhere 21 . The excitation wavelength of 355 nm from a Nd:YAG laser (Continuum Surlite II, third harmonic) was used as the excitation source, coupled with a fast response photomultiplier (Hamamatsu model R5509-72) operated at -80°C in nanosecond flash photolysis experiments (pulse width ca.…”