Dinuclear cyclometalated platinum(ii) complexes containing a deep blue fluorescence chromophore: synthesis, photophysics and application in single dopant white PLEDs

Abstract

To control excimer/aggregation emission and achieve a single active emitter of aggregation for controllable white polymer light-emitting devices (PLEDs), two star-shaped dinuclear platinum(II) complexes of C₆DBCzC₆-DFPt(pic) and DPy(TPA)-C₆DBCzC₆-DFPt(pic) were synthesized and characterized, in which DBCz is a 3,6-diphenyl-carbazole bridged core, C₆ is an unconjugated dioxyhexyloxy linkage, DPy(TPA) is (4,4′-di(pyren-1-yl)triphenylamine), a deep blue-emitting fluorescent chromophore, and DPtF(pic) is a dinuclear platinum(II) [(4,6-difluorophenyl)-pyridinato-N,C^2′](picolinate) blue-emitting phosphorescent chromophore. Compared to its parent complex C₆DBCzC₆-DFPt(pic), DPy(TPA)-C₆DBCzC₆-DFPt(pic) showed a lower lying highest occupied molecular energy level (HOMO) and lowest unoccupied molecular energy level (LUMO). Under a current of 2.5 mA, near-white emission was obtained in the DPy(TPA)-C₆DBCzC₆-DFPt(pic)-doped devices at dopant concentrations from 4 wt% to 10 wt%. However, green-yellow emission was obtained in the C₆DBCzC₆-DFPt(pic)-doped devices with the same device configuration using a blend of polyvinylcarbazole (PVK) and 2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD) as a host matrix, respectively. This indicates that incorporating a deep blue fluorescent chromophore into a green-yellow emitting dinuclear platinum(II) complex is an available way to control aggregation/excimer emissions and get white-emitting PLEDs with a single dopant.