Energy transfer and triplet exciton confinement in polymeric electrophosphorescent devices

Chen, Fang‐Chung; Chang, Shu Chen; He, Gufeng; Pyo, Seungmoon; Yang, Yang; Kurotaki, Masayuki; Kido, Junji

doi:10.1002/polb.10648

Cited by 146 publications

(134 citation statements)

References 33 publications

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“…We expected poly(3,6-fluorene) might have wider bandgap and much higher triplet energy level than poly(2,7-fluorene), and as a result it could be a good conjugated host material for the blue-and green-light-emitting triplet guests. In this Communication, we report the synthesis of a novel conjugated homopolymer, poly (9,9 0 -bis(2-ethylhexyl)-3, 6-fuorene) (P36EHF), with a wide bandgap of 3.65 eV showing PL and electroluminescence (EL) emission in the UV region peaked at around 344 and 400 nm, respectively. We have also shown that P36EHF has a triplet energy level at around 2.6 eV much higher than that of poly(2,7-fluorene)s. Therefore P36EHF can be a good host material for green-and even blue-light-emitting triplet emitters, such as iridium(III) fac-tris(2-phenylpyridine) (Ir(ppy) 3 ) and iridium(III) bis [2-…”

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confidence: 99%

“…The detailed procedure for synthesis of the monomer and intermediates and their characterization can be found in the Supporting Information (SI). The nickel-catalyzed Yamamato coupling polymerization was employed to obtain the desired homopolymer, poly (9,9 0 -bis(2-ethylhexyl)-3,6-fluorene, in good yield (80%). The polymer was readily soluble in common organic solvents such as chloroform, tetrahydrofuran (THF), and toluene.…”

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confidence: 99%

“…[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).…”

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High‐Triplet‐Energy Poly(9,9′‐bis(2‐ethylhexyl)‐3,6‐fluorene) as Host for Blue and Green Phosphorescent Complexes

Xiong

Zou

et al. 2008

Advanced Materials

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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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confidence: 99%

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confidence: 99%

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High‐Triplet‐Energy Poly(9,9′‐bis(2‐ethylhexyl)‐3,6‐fluorene) as Host for Blue and Green Phosphorescent Complexes

Xiong

Zou

et al. 2008

Advanced Materials

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“…Dexter transfer was considered to be unlikely since the T 1 level of PVK is lower in energy than the T 1 level of dbm, ∼ 2.5 and 2.6 eV, respectively. [8,25] The expected efficacy of energy transfer was evaluated by estimating the Förster radius R 0 , defined as the acceptordonor distance at which the probability of Förster energy transfer is equal to that of donor de-excitation by fluorescence or other processes, as follows:…”

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confidence: 99%

Emission Colour Tuning in Semiconducting Polymer Nanotubes by Energy Transfer to Organo‐ Lanthanide Dopants

Moynihan¹,

Iacopino²,

O’Carroll³

et al. 2007

Advanced Materials

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One-dimensional (1D) nanostructures based on molecular and polymeric materials are attracting significant research interest due to the many novel chemical, physical and electronic properties that may arise in highly anisotropic systems and the possibility for exploitation of such properties in a wide variety of applications. [1] In particular, the potential of semiconducting polymer nanowires and nanotubes has already been explored for initial demonstration of nanoelectronic and nanophotonic devices such as field effect transistors, [2] field emitters, [3] and sub-wavelength optically pumped lasers, [4] photodetectors [5] and electroluminescent diodes. [6] Successful realization of such devices will rely upon the ability to tune the opto-electronic characteristics of the constituent materials. For applications based on optical emission such as tagging, sensing, and electroluminescence, the ability to obtain pure emission colors will be essential, especially where multiplexing of optical signals, e.g., from distinct individual nanowire light sources, may be involved. However, it is difficult to achieve emission color purity in semiconducting polymers since their emission spectra have a large full-width-at-halfmaximum due to both inhomogeneous broadening and the presence of a vibronic progression. Emission color tuning in polymers has been addressed by the incorporation of luminescent chromophores such as fluorescent organic dyes, [7] phosphorescent metal complexes [8,9] and inorganic quantum dots.[10] These dopants "harvest" host matrix excitations by charge trapping and/or fluorescence resonance energy transfer processes, i.e., dipole-dipole coupling (Förster energy transfer) [11] and electron exchange (Dexter energy transfer), [12] allowing precise tuning of emission wavelength and color purity. The long-lived and near monochromatic emission of rare-earth ions, arising from weakly allowed f-f emissive transitions that are well shielded from the local environment by 5s 2 and 5p 6 electrons, has also made them attractive chromophores for such purposes.[13] While lanthanide ions are themselves insoluble in polymers, encapsulation of the ions with organic ligands as organo-lanthanide chelates allows incorporation within polymer hosts. These complexes may be designed to exploit the "antenna effect" to enhance the effective absorption cross sections of the lanthanide ions via the mechanism of ligand sensitization. [14] Ligand properties may be further tailored to ensure that a significant overlap between the host emission spectrum and the absorption spectrum of the ligands exists to permit efficient Förster energy transfer between host and dopants. [15] In this paper, we report the tuning of emission chromaticity in semiconducting polymer nanotubes by energy transfer from the host polymer to luminescent chromophore dopants. Poly(N-vinylcarbazole) (PVK), a blue emissive, hole conducting polymer was selected as the host matrix. This versatile polymeric semiconductor has been previously employed in applications ranging ...

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“…10 Therefore, better matching between the host material and deep blue dopant material with sufficient spectral overlap for Förster energy transfer 11 is required for deep blue emission with high efficiency. [12][13][14][15][16][17][18][19][20] Also, an OLED's quantum efficiency is determined by the carrier injection and recombination in the emitting layer (EML); therefore, the balance between electrons and holes in the EML is the most important factor to obtain higher quantum efficiency. This study contributes to the understanding of significant effects of double EMLs and host-dopant systems of blue OLEDs with 4,4'-bis (9-ethyl-3-carbazovinylene)-1,1'biphenyl (BCzVBi) doped to two different host materials of 4,4-bis (2,2-diphenylyinyl)-1,10-biphenyl (DPVBi) and 9,10-bis (2-naphthyl) anthracene (ADN).…”

Section: Introductionmentioning

confidence: 99%

Highly efficient blue organic light-emitting diodes using dual emissive layers with host-dopant system

Lee

Kim

et al. 2013

J. Photon. Energy

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Abstract. We fabricated highly efficient blue organic light-emitting diodes (OLEDs) by designing differing emitting layer structures with fluorescent host and dopant materials of 4,4-bis (2,2-diphenylyinyl)-1,10-biphenyl and 9,10-bis (2-naphthyl) anthracene as host materials and 4,4'-bis (9-ethyl-3-carbazovinylene)-1,1'biphenyl (BCzVBi) as a dopant material to demonstrate electrical and optical improvements. Best enhancement in luminance and luminous efficiency were achieved by a quantum well structure in device F with 8668 cd∕m 2 at 8 V and 5.16 cd∕A at 103.20 mA∕cm 2 , respectively. Among the blue OLED devices doped by BCzVBi, device B emits the deepest blue emission with Commission Internationale de l'É clairage coordinates of (0.157, 0.117) at 8 V. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

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Energy transfer and triplet exciton confinement in polymeric electrophosphorescent devices

Cited by 146 publications

References 33 publications

High‐Triplet‐Energy Poly(9,9′‐bis(2‐ethylhexyl)‐3,6‐fluorene) as Host for Blue and Green Phosphorescent Complexes

High‐Triplet‐Energy Poly(9,9′‐bis(2‐ethylhexyl)‐3,6‐fluorene) as Host for Blue and Green Phosphorescent Complexes

Emission Colour Tuning in Semiconducting Polymer Nanotubes by Energy Transfer to Organo‐ Lanthanide Dopants

Highly efficient blue organic light-emitting diodes using dual emissive layers with host-dopant system

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