Synthesis and optoelectronic properties of dinuclear cyclometalated platinum (II) complexes containing naphthalene-functionalized carbazole groups in the single-emissive-layer WPLEDs

Abstract

To tune excimer/aggregation emission and obtain single emissive dopants for white polymer light-emitting diodes (WPLEDs), two novel star-shaped dinuclear cyclometalated platinum (II) complexes, namely DPtF(pic)C6TPhC6D(dHCz) and DPtF(pic)C6TPhC6D(dNaCz), have been synthesized and characterized, where DPtF(pic) is dinuclear platinum (II) [(4,6-difluorophenyl)-pyridinato-N,C2′](picolinate) blue-emitting phosphorescent chromophore, D(dHCz) and D(dNaCz) are blue emitting fluorescent chromophores containing carbazole or naphthalene functionalized carbazole group, respectively, TPh is p-terphenyl used as central bridging core, finally, each parts of molecular skeleton are wired through nonconjugated hexyloxy ether linkage (C6). Their thermal, electrochemical and optophysical properties were primarily investigated. The device fabricated with these complexes doped into a host polyvinylcarbazole (PVK) blend with 30 wt % of an electron transport material 1,3-bis-(5-(4-(tert-butyl)phenyl)-1,3,4-oxadiazol-2-yl)benzene (OXD-7) showed near-white emission at lower dopant concentration. At 1 wt % dopant concentration, DPtF(pic)C6TPhC6D(dHCz) exhibited near-white emission with a luminous efficiency (LE) of 1.12 cd/A and a maximum external quantum efficiency (EQE) of 0.57% (Commission Internationale de I'Eclairage(CIE) chromaticity coordinates: (0.27, 0.40)) at 2.72 mA/cm2. At the same dopant concentration, DPtF(pic)C6TPhC6D(dNaCz) showed much tunable near-white emission with a LE of 0.99 cd/A and a EQE of 0.51% (CIE: 0.30, 0.41) at 0.87 mA/cm2.