During the last two decades, organic and polymer lightemitting devices (OLEDs/PLEDs) have been the subject of intense academic and industrial research because of their potential applications in full-color flat-panel displays and solid-state lighting. [1][2][3] Recently, phosphorescent PLEDs, in which heavy metal complexes (such as Ir and Pt complexes) are doped into appropriate polymer host materials, have attracted increasing interest owing to the possible full utilization of both singlet and triplet excitons combined with solution processability.[4] Many studies [5] have shown that in order to realize high device efficiency, in phosphorescent PLEDs, the triplet energy state (E T ) of the polymer host should be located at higher energy than that of the guest complexes. Otherwise, triplet excitons on the guest could undergo back-transfer to the triplet state of the host, and as a result the host polymer would become a luminescence quencher of triplet emitters.[6] Since most conjugated polymers have a low-lying triplet state, so far only red-phosphorescent PLEDs with a conjugated polymer as the host have shown high device efficiency. [7] For green-and blue-light-emitting triplet emitters [8] with typically a higher triplet state than that of conjugated polymers, [9] the devices with the conjugated polymer host are poor. Therefore for green-and blue-light-emitting triplet devices, typically nonconjugated poly(vinylcarbazole) (PVK) has been used as the polymer host, since PVK has a relatively high triplet energy state (2.5 eV).[5c] Since PVK is a nonconjugated polymer with high resistivity, typically, the operating voltage of these devices is relatively high. Therefore in order to obtain phosphorescent PLEDs with high efficiency and low power consumption, it is crucially important to develop a wide-bandgap conjugated polymer host with high-lying triplet energy state.The most widely used polymer hosts for fluorescent guest dyes are poly(2,7-fluorene)s and their derivatives, owing to their wide bandgap, high photoluminescence (PL) quantum efficiency, and excellent conductivity.[10] However, many authors have reported that poly(2,7-fluorene)s are not a good host for blue-and green-light-emitting triplet complexes because of their low-lying triplet energy state (2.15-2.3 eV).[5b,5d,6a] Surprisingly, despite poly(2,7-fluorene)s having been investigated for many years, there have been almost no reports on a fluorene homopolymer with fluorene units linked at the 3,6 position. As poly(3,6-carbazole)s [8,11] and poly(3,6-silafluorene)s [12] show higher triplet energy levels than their 2,7-counterparts, we thought it of interest to synthesize poly(3,6-fluorene)s and investigate their photophysical properties. The group of van Dijken and Brunner reported a 3,6-spirofluorene copolymer and oligomers with carbazole. [8a,13] Recently, Mo et al. [14] reported synthesis of poly(3,6-fluorene) by Ni-catalyzed coupling, but their polymer showed a strange and extremely broad PL spectra in the film and neither detailed photophysical p...

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High quality PbS nanocrystals are synthesized reproducibly through lead stearate and sulfur stabilized by oleylamine in a non-coordinating solvent. The morphology, crystalline form and phase composition of PbS nanocrystals are examined by transmission electron microscopy (TEM), high-resolution TEM, x-ray diffraction (XRD), energy-dispersive x-ray spectroscopy (EDS) and x-ray photoelectron spectroscopy (XPS). The as-synthesized PbS nanocrystals have strong absorption and photoluminescence emissions in the near-infrared region. The size of PbS nanocrystals from 5 to 13 nm can be adjusted through the optimization of the synthesis conditions. The smaller PbS nanoparticles are obtained at the lower reaction temperature, lower precursor concentration, larger oleylamine quantity and larger lead precursor/sulfur ratio. The basic oleylamine enhances the reactivity of both lead stearate precursor and sulfur precursor in the reaction.