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Issue 45, 2013
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Mechanoluminescent and efficient white OLEDs for Pt(II) phosphors bearing spatially encumbered pyridinyl pyrazolate chelates

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Three Pt(II) complexes with a formula of [Pt(Lx)2], x = 1, 2 and 3, in which the pyrazole chelate (Lx)H represents 4-(2,6-diisopropylphenyl)-2-(3-trifluoromethyl-1H-pyrazol-5-yl)pyridine (1), 5-(2,6-diisopropylphenyl)-2-(3-trifluoromethyl-1H-pyrazol-5-yl)pyridine (2) and 4-(tert-butyl)-2-(3-trifluoromethyl-1H-pyrazol-5-yl)pyridine (3), were synthesized, and their photophysical properties were examined. Single-crystal X-ray diffraction studies of 1 and 2 reveal a planar molecular geometry with both Lx chelates adopting a mutually trans configuration. Distinctive packing arrangements within the crystal lattices are observed, e.g., complex 2 shows structural repetitions that prohibit formation of intimate π–π stacking, while complex 1 exhibits an ordered alignment along the axis of the square planar core framework and, remarkably, shows mechanoluminescence and concentration dependent photoluminescence in the poly(methyl methacrylate) matrix (PMMA). In sharp contrast, derivatives 2 and 3 show only the luminescence derived from the monomeric and aggregated state, respectively, which is attributed to the imposed substituent effect. For application, organic light emitting diodes (OLEDs) were also fabricated using the aforementioned blue dopant 1, attaining the peak external quantum efficiency, current and power efficiencies of ηext = 9.1%, ηc = 18.4 cd A−1 and ηp = 16.6 lm W−1 respectively. With the same device structure, devices based on 3 exhibit an extremely high efficiency orange emission (20.0%, 47.6 cd A−1, 50.8 lm W−1) due to the occurrence of extensive π–π-stacking. Upon combining blue-emitting phosphor 1 and orange-emitting phosphor 3, two white OLED devices are fabricated, one of which obtained by sequentially doping 1, 3 and then 1 into separated layers exhibits performance efficiencies of 11.3%, 28.3 cd A−1, and 21.2 lm W−1, highly stable chromaticity (CIEx = 0.41–0.40 and CIEy = 0.43–0.41), and an adequate color-rendering index (CRI) of 80 at brightness of 370 to 10 800 cd m−2. The other device obtained by co-doping 1 and 3 into a single emissive layer shows improved efficiencies of 15.0%, 44.8 cd A−1, and 46.2 lm W−1, but with a lower CRI of 63.

Graphical abstract: Mechanoluminescent and efficient white OLEDs for Pt(ii) phosphors bearing spatially encumbered pyridinyl pyrazolate chelates

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Publication details

The article was received on 06 Aug 2013, accepted on 13 Sep 2013 and first published on 16 Sep 2013

Article type: Paper
DOI: 10.1039/C3TC31524J
Citation: J. Mater. Chem. C, 2013,1, 7582-7592
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    Mechanoluminescent and efficient white OLEDs for Pt(II) phosphors bearing spatially encumbered pyridinyl pyrazolate chelates

    L. Huang, G. Tu, Y. Chi, W. Hung, Y. Song, M. Tseng, P. Chou, G. Lee, K. Wong, S. Cheng and W. Tsai, J. Mater. Chem. C, 2013, 1, 7582
    DOI: 10.1039/C3TC31524J

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