Selective formation of amorphous, nematic (N), and beta phases in poly(9,9-di-n-octyl-2,7-fluorene) (PFO) films was achieved via judicious choice of process parameters. Phase structure and film morphology were carefully examined by means of X-ray diffraction as well as electron microscopy. "Amorphous" thin films were obtained by quick evaporation of solvent. Slow solvent removal during film formation or extended treatment of the amorphous film with solvent vapor resulted in predominantly the beta phase, which corresponds to a frozen (due to decreased segmental mobility upon solvent removal) and intrinsically metastable state of transformation midway between a solvent-induced clathrate phase and the equilibrium crystalline order in the undiluted state. The frozen transformation process is reactivated upon an increase in temperature beyond 100 degrees C. Compared to the amorphous film, extended backbone conjugation in the beta phase is evidenced from the emergence of a characteristic absorption peak around 430 nm near the absorption edge. For films of frozen nematic order (obtained by quenching from the nematic state), the conjugation length is also greater than the amorphous films as revealed by an absorption shoulder around 420 nm. Well-behaved single-chromophore emission with single-mode phonon coupling was observed for the beta phase; in the case of nematic films, dual-mode phonon coupling must exist if single-chromophore emission is assumed. In comparison, the emission spectrum of the amorphous film of generally shorter conjugation lengths exhibited mixed characteristics of nematic and beta phases, implying the presence of minor populations of extended conjugation similar to those in nematic and beta phases, which are of biased weightings in the emission spectra. All these films consist of nanograins (ca. 10 nm in size) of collapsed chains; the films are therefore inherently inhomogeneous in this length scale. In combination with previous observations on the crystalline (alpha and alpha') forms, the phase behavior of PFO is then generally summarized in terms of relative thermodynamic stability. 相似文献
Triple-layer-type organic electroluminescent devices were fabricated using charge-transporting poly(N-vinylcarbazole) (PVK) as a hole-transporting emitter layer. Electron-transporting layers consisting of a triazole derivative (TAZ) and an aluminum complex (Alq) layer were used to maximize the carrier recombination efficiency. The EL device with a structure of glass substrate/indium-tinoxide/PVK/TAZ/AIq/Mg:Ag showed bright blue emission from the PVK layer with a luminance of over 700 cd/m2. The emission color was tuned to a desirable color in the visible region through doping the PVK layer with fluorescent dyes. Bright white emission, in particular, was obtained for the first time at a high luminance level of over 3000 cd/m2 by using three kinds of fluorescent dyes each emitting red, green or blue. 相似文献
Steady-state and time-resolved photoluminescence have been used to investigate the optical properties of bilayer and blend films made from poly(9,9-dioctyl-fluorene-2,7-diyl) (PFO) and poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH PPV). Energy transfer has been observed in both systems. From steady-state photoluminescence measurements, the energy transfer was characterized by the effective enhancement of the MEH PPV emission intensity after exciting the donor states. Relatively faster decays for the PFO donor emission have been observed in the blends as well as in the bilayer structures, confirming effective energy transfer in both structures. In contrast to the bilayers, the time decay of the acceptor emission in the blends presents a long decay component, which was assigned to the exciplex formation in these samples. For the blends the acceptor emission is in fact a composition of exciplex and MEH PPV emissions, the later being due to Fo?rster energy transfer from PFO. In the bilayers, the exciplex is not observed and temperature dependence photoluminescence measurements show that exciton migration has no significant contribution to the energy transfer. The efficiency and very long range of the energy transfer in the bilayers is explained assuming a surface-surface interaction geometry where the donor/acceptor distances involved are much longer than the common Fo?rster radius. 相似文献
We report on the heterobimetallic system, Eu[Ag(x)Au(1-x)(CN)(2)](3) (x = 0-1) in which sensitization of europium luminescence occurs by energy transfer from [Ag(x)Au(1-x)(CN)(2)](-) donor excited states. The donor states have energies which are tunable and dependent on the Ag/Au stoichiometric ratio. These layered systems exhibit interesting properties, one of which is their emission energy tunability when excited at different excitation wavelengths. In this paper, we report on their use as donor systems with Eu(III) ions as acceptor ions in energy transfer studies. Luminescence results show that the mixed metal dicyanides with the higher silver loading have a better energy transfer efficiency than the pure Ag(CN)(2)(-) and Au(CN)(2)(-) donors. The better energy transfer efficiency is due to the greater overlap between the donor emission and acceptor excitation. Additionally, more acceptor states are available in the high silver loading mixed metal Eu(III) complexes. The results from a crystal structure determination and Raman experiments are also presented in this paper and provide information about metallophilic interactions in the closed-shell d(10) metal-metal [Ag(x)Au(1-x)(CN(2)](-) dicyanide clusters. 相似文献
We have designed and synthesized a series of deep-blue light-emitting polyfluorenes, PF-27SOs and PF-36SOs, by introducing electron-deficient 9,9-dimethyl-9H-thioxanthene 10,10-dioxide isomers (27SO and 36SO) into the poly(9,9-dioctylfluorene) (PFO) backbone. Compared with PFO, the resulting polymers exhibit an equivalent thermal decomposition temperature (>415 °C), an enhanced glass transition temperature (>99 °C), a decreased lowest unoccupied molecular orbital energy level (ELUMO) below −2.32 eV, a blue-shifted photoluminescence spectra in solid film with a maximum emission at ~422 nm, and a shoulder peak at ~445 nm. The resulting polymers also show blue-shifted and narrowed electroluminescence spectra with deep-blue Commission Internationale de L'Eclairage (CIE) coordinates of (0.16, 0.07) for PF-27SO20 and (0.16, 0.06) for PF-36SO30, compared with (0.17, 0.13) for PFO. Moreover, simple device based on PF-36SO30 achieves a superior device performance with a maximum external quantum efficiency (EQEmax = 3.62%) compared with PFO (EQEmax = 0.47%). The results show that nonconjugated 9,9-dimethyl-9H-thioxanthene 10,10-dioxide isomers can effectively perturb the conjugation length of polymers, significantly weaken the charge-transfer effect in donor–acceptor systems, substantially improve electroluminescence device efficiency, and achieve deep-blue light emission. 相似文献
Summary: Blends of poly(9,9‐dioctylfluorene) (PFO) and poly(2‐methoxy‐5(2′‐ethyl‐hexyloxy)‐1,4‐phenylenevinylene) (MEH‐PPV) were found to phase separate into 40–50 nm crystalline PFO domains and to exhibit efficient white electroluminescence when the composition is below 30 wt.‐% MEH‐PPV. The 5 wt.‐% nanocrystalline blends had a luminance of 4 000 cd · m−2, an external quantum efficiency of 3.1%, and a current efficiency of 3.7 cd · A−1. Transmission electron microscopy, electron diffraction, and atomic force microscopy of blends with higher MEH‐PPV content and the two homopolymers showed them to be amorphous. Only orange‐red electroluminescence, characteristic of MEH‐PPV, was observed from the amorphous blends due to efficient energy transfer from PFO. These results demonstrate that energy transfer processes in binary PFO:MEH‐PPV blends and light‐emitting devices based on them can be controlled through the morphology and composition.
Organic light‐emitting diodes (OLEDs) have been greatly developed in recent years owing to their abundant advantages for full‐color displays and general‐purpose lightings. Blue emitters not only provide one of the primary colors of the RGB (red, green and blue) display system to reduce the power consumption of OLEDs, but are able able to generate light of all colors, including blue, green, red, and white by energy transfer processes in devices. However, it remains a challenge to achieve high‐performance blue electroluminescence, especially for nondoped devices. In this paper, we report a blue light emitting molecule, DPAC‐AnPCN, which consists of 9,9‐diphenyl‐9,10‐dihydroacridine and p‐benzonitrile substituted anthracene moieties. The asymmetrically decoration on anthracene with different groups on its 9 and 10 positions combines the merits of the respective constructing units and endows DPAC‐AnPCN with pure blue emission, high solid‐state efficiency, good thermal stability and appropriate HOMO and LUMO energy levels. Furthermore, DPAC‐AnPCN can be applied in a nondoped device to effectively reduce the fabrication complexity and cost. The nondoped device exhibits pure blue electroluminescence (EL) locating at 464 nm with CIE coordinates of (0.15, 0.15). Moreover, it maintains high efficiency at relatively high luminescence. The maximum external quantum efficiency (EQE) reaches 6.04 % and still remains 5.31 % at the luminance of 1000 cd m?2 showing a very small efficiency roll‐off. 相似文献
Green emission in polyfluorenes (PFs) has been attributed to aggregation or excimer emission, but recently it was reassigned as an on-chain fluorenone defect. We show here that, in dialkyl-substituted PFs that is hydrogen-free at the 9'-position of the fluorene, blue emission with very weak green emission is observed from end-capped polydioctylfluorene (PFO) for both photoluminescence and electroluminescence spectra, while the low-energy green emission at 507 nm is very pronounced only in uncapped PFO (PFOun). The facts that there is no detectable infrared absorption at around 1721 cm(-1) due to >C=O stretching vibration in PFOun and no charge-trapping occurring in the light-emitting device from PFOun are in contrast with those found in the literature-reported copolymers with fluorenone units, which have detectable infrared absorption at 1721 cm(-1) and charge-trapping in devices. We found that this green emission at around 507 nm originates from the end-group-enhanced aggregation by use of UV-vis absorption, photoexcitation spectra, and steady-state photoluminescent and electroluminescent spectra. The end-group-enhanced aggregation is much weaker in other PFs with less-ordered structures. 相似文献
Poly(9,9-dioctylfluorene) (PFO) shows highly efficient blue emission with photo excitation occurring between 340–400 nm. Here
we show that PFO can in dilute solution emit at a wavelength well below that at which it is being exited. This, we propose
is related to an energy transfer from conjugated parts of the polymer chain into more localised states which then emit at
a lower wavelength. These localised states can be considered as defects in the conjugation of the polymer or as chain ends.
These may produce quasi monomer or quasi dimer species within the chain, which will have a HOMO-LUMO gap of higher energy
than the conjugated polymer. These then fluoresce at the lower wavelength; essentially causing, by energy transfer, a process
of energy up-conversion.
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We report the synthesis of a new pyrene, dipicolinic acid-based ligand ( L1H ) and its corresponding multi-emissive and multifunctional europium complex [Eu( L1 )3] that is capable of single component color switchable emission from red to blue and also white. At high concentration (10 mM) the single component system results in near pure white emission (CIE coordinates x,y=0.329, 0.324). Furthermore, the system showed ratiometric oxygen sensing with oxygen significantly quenching the pyrene centered emission but not the Eu3+ emission, resulting in an overall emission color change from blue to red on increasing oxygen content. 相似文献
Highly fluorescent nanoparticles of the conjugated polymer poly(9,9-dioctylfluorene) (PFO) with distinct phases were prepared, and their photophysical properties were studied by steady state and time-resolved fluorescence spectroscopy. An aqueous suspension of PFO nanoparticles prepared by a reprecipitation method was observed to exhibit spectroscopic characteristics consistent with the glassy phase of the polymer. We demonstrate that controlled addition of organic solvent leads to partial transformation of the disordered polymer chains into the planarized conformation (beta-phase), with the fractions of each component phase dependent on the amount of solvent added. Fluorescence spectroscopy of the PFO nanoparticles containing beta-phase indicates efficient energy transfer from the glassy-phase regions of the nanoparticles to the beta-phase regions. Salient features of the nanoparticles containing beta-phase include narrow, red-shifted fluorescence and increased fluorescence quantum yield as compared to the glassy-phase nanoparticles. Fluorescence lifetime measurements indicate that the increased quantum yield of the beta-phase PFO originates from a decrease in the nonradiative decay rate, with little change in the radiative rate. This decrease is likely due to exciton trapping by the beta-phase, which leads to a reduction in the energy transfer efficiency to quencher species present within the nanoparticle. 相似文献
An electron transporting moiety (1,3,4-oxadiazole) and a hole transporting moiety (carbazole) were combined to create 2-(4-biphenylyl)-5-(4-carbazole-9-yl)phenyl-1,3,4-oxadiazole (CzOxa), a three layer device with a configuration of ITO/TPD(50 nm)/CzOxa(40 nm)/AlQ(40 nm)/Mg0.9Ag0.1(200 nm)/Ag(80 nm) which exhibited a blue emission peak at approximately 470 nm (x = 0.14, y = 0.19) with a maximum luminance of 26,200 cd m(-2) at a drive voltage of 15 V and a maximum luminous efficiency of 2.25 lm W(-1). 相似文献
The electrochemical reaction of lithium with a vacancy-containing titanium hydroxyfluoride was studied. On the basis of pair distribution function analysis, NMR, and X-ray photoelectron spectroscopy, we propose that the material undergoes partitioning upon initial discharge to form a nanostructured composite containing crystalline Li(x)TiO(2), surrounded by a Ti(0) and LiF layer. The Ti(0) is reoxidized upon reversible charging to an amorphous TiF(3) phase via a conversion reaction. The crystalline Li(x)TiO(2) is involved in an insertion reaction. The resulting composite electrode, Ti(0)-LiF/Li(x)TiO(2) ? TiF(3)/ Li(y)TiO(2), allows reaction of more than one Li per Ti, providing a route to higher capacities while improving the energy efficiency compared to pure conversion chemistries. 相似文献