Synthesis, optoelectronic properties of a dinuclear platinum(II) complex containing a binary cyclometalated ligand in the single-emissive-layer PLEDs.

A novel dinuclear platinum complex of (dfppy-mhb-dfppy)Pt(2)(acac)(2) was synthesized and characterized, where dfppy-mhb-dfppy is a binary C^N cyclometalated ligand containing two bridged 2,4-difluorophenylpyridine (dfppy) units and acac is 2,4-pentanedione anion. Compared to previously reported dinuclear platinum complexes with a binary ancillary ligand, this dinuclear platinum complex showed more intense excimer emission, peaking at 617 nm, besides its intrinsic emission in dilute dichloromethane solution. Single-emissive-layer (SEL) polymer light-emitting devices (PLEDs) using (dfppy-mhb-dfppy)Pt(2)(acac)(2) as dopant and a blend of poly (N-vinylcarbazole) (PVK) and 2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD) as host matrix exhibited stable white emission at 1 wt% doping concentration under applied voltages from 7 V to 11 V. The stable white emission observed in the (dfppy-mhb-dfppy)Pt(2)(acac)(2)-doped SEL PLEDs indeed implies that the dinuclear platinum complex constructed by a binary cyclometalated ligand has a potential application in white-emitting SEL PLEDs.

Star-shaped trinuclear cyclometalated platinum(II) complexes as single-component emitters in white-emitting PLEDs.

Two star-shaped phosphorescent small molecules, Ph-3FPt(pic) and 4Ph-3FPt(pic), are single-component emitters in polymer white-light-emitting diodes (WPLEDs) that are comprised of three blue-light-emitting phosphorescent chromophores of FPt(pic) and are attached to benzene-1,3,5-trioxy- and 1,3,5-tri(4-oxyphenyl)benzene cores through a hexyloxy chain, respectively. Compared to their corresponding mono- or dinuclear platinum complexes, this class of star-shaped homotrinuclear cyclometalated platinum(II) complexes exhibited controllable excimer emission. Stable white/near-white emission was obtained in single-emissive-layer PLEDs by using the Ph-3FPt(pic) or 4Ph-3FPt(pic) as a single dopant and a blend of poly(vinylcarbazole) and 2-(4-biphenyl)-5-(4-tert-butyl-phenyl)-1,3,4-oxadiazole as a host matrix at dopant concentrations of 1-4 wt.%. Our results provide an efficient way to control excimer formation and to obtain a single-component emitter for use in WPLEDs.

Synthesis and optoelectronic properties of a heterobimetallic Pt(II)-Ir(III) complex used as a single-component emitter in white PLEDs.

To tune aggregation/excimer emission and obtain a single active emitter for white polymer light-emitting devices (PLEDs), a heterobimetallic Pt(II)-Ir(III) complex of FIr(pic)-C(6)DBC(6)-(pic)PtF was designed and synthesized, in which C(6)DBC(6) is a di(phenyloxyhexyloxy) bridging group, FIr(pic) is an iridium(III) bis[(4,6-difluorophenyl)pyridinato-N,C(2)'] (picolinate) chromophore and FPt(pic) is a platinum(II) [(4,6-difluorophenyl)pyridinato-N,C(2)'] (picolinate) chromophore. Its physical and opto-electronic properties were investigated. Interestingly, the excimer emission was efficiently controlled by this heterobimetallic Pt(II)-Ir(III) complex compared to the PL profile of the mononuclear FPt(pic) complex in the solid state. Near-white emissions were obtained in the single emissive layer (SEL) PLEDs using this heterobimetallic Pt(II)-Ir(III) complex as a single dopant and poly(vinylcarbazole) as a host matrix at dopant concentrations from 0.5 wt% to 2 wt%. This work indicates that incorporating a non-planar iridium(III) complex into the planar platinum(II) complex can control aggregation/excimer emissions and a single phosphorescent emitter can be obtained to exhibit white emission in SEL devices.

Synthesis and optoelectronic properties of a carbazole-modified platinum(II) complex in polymer light-emitting devices.

To improve opto-electronic properties and efficiently suppress excimer emission, a phenylpyridine (ppy)-based platinum(II) complex (C(16)OCz-ppy)Pt(acac) was synthesized and characterized, where C(16)OCz-ppy is a 2-phenylpyridine derivative appending a carbazole moiety and three hexadecyloxy methyl units in the parent phenylpyridine, and acac is acetylacetone. This carbazole-modified platinum(II) complex exhibited good thermal stability and three times higher photoluminescent quantum yield than its parent (2-phenylpyridine-C(2),N)(2,4-pentanedionato-O,O)platinum(II) complex [(ppy)Pt(acac)]. Single-emissive-layer polymer light-emitting devices using (C(16)OC(Z)-ppy)Pt(acac) as dopant and a blend of poly(N-vinylcarbazole) and 2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole as host matrix presented a maximum current efficiency of 1.51 cd A(-1), which was 1.5 times higher than that from the (ppy)Pt(acac)-doped device with the same device structure. Little excimer emission and minor aggregation emission were observed in the (C(16)OC(Z)-ppy)Pt(acac)-doped PLEDs at different dopant concentrations and applied voltages. This work indicates that introducing a carbazole and three hexadecyloxy methyl groups into the planar platinum(II) complex can reduce molecular aggregation and excimer emissions, thus resulting in high luminance and stable EL spectra in comparison with the parent (ppy)Pt(acac).

Metallomesogens based on platinum(II) complexes: synthesis, luminescence and polarized emission.

Two series of heteroleptic cyclometalated platinum(II) complexes [(C(n)Oppy)Pt(acac) and (C(n)OFppy)Pt(acac)] have been prepared. Their liquid-crystal and optophysical properties were studied, in which C(n)Oppy is 2-(4-alkoxyphenyl)-5-(alkoxymethyl)pyridine and C(n)OFppy is 2-(3-fluoro-4-alkoxyphenyl)-5-(alkoxymethyl)pyridine. Only the heteroleptic cyclometalated platinum(II) complexes (n = 12 and 16) exhibited enantiotropic mesophase transitions with smectic (S(m)) structure. Intense polarized luminescence with a maximum peak at 532 nm and a polarization ratio as high as 10.5 were obtained in an aligned polyimide film under opto-excitation at room temperature. This research work provides a simple approach to realize high-efficiency polarized emission by heteroleptic cyclometalated platinum(II) complexes.