White polymeric light-emitting diode based on a fluorene polymer∕Ir complex blend system

WOLEDs offer new design opportunities in practical solid-state lighting and could play a significant role in reducing global energy consumption. Obtaining white light from organic LEDs is a considerable challenge. Alongside the development of new materials with improved color stability and balanced charge transport properties, major issues involve the fabrication of large-area devices and the development of low-cost manufacturing technology. This Review will describe the types of materials (small molecules and polymers) that have been used to fabricate WOLEDs. A range of device architectures are presented and appraised.

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“…4). [48] A peak EQE of 2.8% and luminance of 16 000 cd m À2 at applied voltage of 5 V (i.e., 4.57 cd A…”

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Recent Advances in White Organic Light‐Emitting Materials and Devices (WOLEDs)

2010

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“…PF2/6 has potential in thin-film device applications as a white light emitting diode made via "doping" with rubrene 19 or star-like tris-cyclometalated oligofluorenylpyridine iridium͑III͒ ͓Ir͑Fl x Py͒ 3 ͔ guests. 20,21 If polarized white emitters of high charger mobility, achieved via alignment, are desired, it is important to understand how these guest molecules perturb alignment and crystallite orientation.To date, the crystallite orientation has been studied only in pure PF2/6, 18 and therefore there is an interest to extend this work for the host-guest system. The ultimate question is whether guest molecules tune the equatorial crystallite orientation while still maintaining a reasonable degree of meridional orientation.…”

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Influence of star-like iridium complexes in the graphoepitaxy of polyfluorene thin films

et al. 2006

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We report on the impact on the equatorial and meridional orientation in hairy-rod poly͓9,9-bis͑2-ethylhexyl͒-fluorene-2,7-diyl͔ thin films when blended with tris-cyclometalated oligo-fluorenylpyridine iridium͑III͒ complex. The presence of this transition-metal complex does not alter the underlying helical motif of the polymer chain or the hexagonal unit-cell intermolecular packing. However, systematic changes in the resulting texture patterning of the crystallites are observed. Crystallites with two preferred a-b orientations, so called type I and II and differing by 30 degrees, are superimposed on an isotropic background that is designated as type III. The extent of meridional alignment for all three is found to be similar. DOI: 10.1103/PhysRevB.74.214203 PACS number͑s͒: 61.10.Ϫi, 82.35.Lr, 81.07.Bc, 81.16.Dn Manipulating and controlling the molecular-level structure of functionalized polymers in bulk and at surfaces is central to the science and applications of these materials. Hairy-rod polymers 1 are one important example and, among those with -conjugated backbones 2 ͓e.g., poly͑p-phenylenes͒, 3 polyfluorenes ͑PFs͒, 4 and ladder derivatives 5 ͔, the nature of the main chain conformation and interchain packing are crucial factors in ultimately determining optical and transport properties. The structural characteristics at larger length scales are equally as important, and this has been the main emphasis in a number of recent studies. A classic example is the poly͑3-alkylthiophene͒ family 6 in which the extent of structural isomorphism or regioregularity strongly affects the internal crystallite structure 7 and the subsequent structural evolution when intercalated or doped. 8 Among PFs, important blue emitting polymers, even small differences in the molecular structure can influence the charge carrier mobility 9 and fluorescence. 10 Poly͓9,9-bis͑2-ethylhexyl͒-9H-fluorene-2,7-diyl͔ ͑or PF2/6͒ ͑Ref. 11͒ is a well-known helical PF polymer functionalized with branched alkyl side chains. PF2/6's optical properties 12 are relatively insensitive to either changes in the molecular weight ͑MW͒ or processing history, and so it is an excellent model system for studies of intermolecular self-organization. 13 However, this intermolecular assembly is affected by changes in the MW ͑or number averaged MW, M n ͒. In PF2/6, there is a threshold MW, M n * , at which there is a crossover in the phase behavior. 14 Low MW samples exhibit only a single nematic liquid crystal phase ͑n-LC and M n Ͻ M n * ͒ while high MW samples ͑M n Ͼ M n * ͒ include a distinctive thermotropic transition between this n-LC phase and a hexagonal crystalline phase. This threshold MW also marks sharp changes in both meridional alignment 15 and surface morphology. 16 In aligned films on rubbed polyimide ͑PI͒, the rigid PF2/6 lies on the substrate with the helical axes pointing along the rubbing direction ͑denoted z here͒. Consequently, meridional alignment leads to a large absorption and dispersion of the refractive index in the ͑xy0͒ plane along the z...

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“…Since RET can be reasonably ruled out as the dominant mechanism because of the poor spectral overlap, such quenching can be ascribed then only to Dexter energy transfer, which does not require dipole-dipole coupling and mostly relies on the wave function overlap between the donor and acceptor. [32] This is significant only at very short distances (ca. 10 Å) and, given the low degree of π-π stacking of the solidstate film (vide infra), this also tells us that intrachain Dexter energy transfer from the P4T donor to the DAD units is the dominating quenching process.…”

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Triazolobenzothiadiazole‐Based Copolymers for Polymer Light‐Emitting Diodes: Pure Near‐Infrared Emission via Optimized Energy and Charge Transfer

Murto

Minotto

Zampetti

et al. 2016

Advanced Optical Materials

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A series of new near‐infrared (NIR) emitting copolymers, based on a low band gap 6‐(2‐butyloctyl)‐4,8‐di(thiophen‐2‐yl)‐[1,2,3]triazolo[4′,5′:4,5]benzo[1,2‐c]‐[1,2,5]thiadiazole (TBTTT) fluorophore copolymerized into a high band gap poly[3,3′‐ditetradecyl‐2,2′‐bithiophene‐5,5′‐diyl‐alt‐5‐(2‐ethylhexyl)‐4H‐thieno[3,4‐c]pyrrole‐4,6(5H)‐dione‐1,3‐diyl] (P2TTPD) host backbone, for polymer light‐emitting diode (PLED) applications is reported. PLEDs fabricated from the host polymer (P2TTPD‐0) show external quantum efficiencies (EQEs) up to 0.49% at 690 nm, with turn‐on voltage (Von) at only 2.4 V. By incorporating the TBTTT segments into the host polymer backbone, pure NIR emission peaking at ca. 900 nm is obtained with Von remaining below 5 V. This work demonstrates that such a low Von can be attributed to efficient intrachain energy and/or charge transfer to the TBTTT sites. When the NIR emitting copolymer (P2TTPD‐10) is blended with P2TTPD‐0, the TBTTT are confined to well‐separated polymer chains. As a result, the EQE from the blend is lower and the Von higher than that obtained from the pure copolymer (P2TTPD‐1.0) with equal content of TBTTT. An analogous copolymer (P4T‐1.0), consisting of poly[3,3′‐ditetradecyl‐2,2′:5′,2′′:5′′,2′′′‐quaterthiophene‐5,5′′′‐diyl] (P4T) as the host and 1% TBTTT as the NIR emitter, further demonstrates that pure NIR emission can be obtained only through optimized molecular orbital energy levels, as in P2TTPD‐1.0, which minimizes chances for either charge trapping or exciton splitting.

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White polymeric light-emitting diode based on a fluorene polymer∕Ir complex blend system

Cited by 135 publications

References 18 publications

Recent Advances in White Organic Light‐Emitting Materials and Devices (WOLEDs)

Recent Advances in White Organic Light‐Emitting Materials and Devices (WOLEDs)

Influence of star-like iridium complexes in the graphoepitaxy of polyfluorene thin films

Triazolobenzothiadiazole‐Based Copolymers for Polymer Light‐Emitting Diodes: Pure Near‐Infrared Emission via Optimized Energy and Charge Transfer

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