PVK Emission Research Articles

Dual and Multi-Emission Hybrid Micelles Realized through Coordination-Driven Self-Assembly.

Building novel functional nanomaterials with a polymer is one of the most dynamic research fields at present. Here, three amphiphilic block copolymers of 8-hydroxyquinoline derivative motifs (MQ) with excellent coordination function were synthesized by Reversible Addition-Fragmentation Chain Transfer Polymerization (RAFT) polymerization. The coordination micelles were prepared through the self-assembly process, which the MQ motifs were dispersed in the hydrophobic polystyrene (PSt) blocks and hydrophilic Poly(N-isopropylacrylamide (PNIPAM)) blocks, respectively. The dual-emission micelles including the intrinsic red light emission of quantum dots (QDs) and the coordination green light emission of Zn2+-MQ complexes were built by introducing the CdSe/ZnS and CdTe/ZnS QDs in the core and shell precisely in the coordination micelles through the coordination-driven self-assembly process. Furthermore, based on the principle of three primary colors that produce white light emission, vinyl carbazole units (Polyvinyl Carbazole, PVK) with blue light emission were introduced into the hydrophilic PNIPAM blocks to construct the white light micelles that possess special multi-emission properties in which the intrinsic red light emission of QDs, the coordination green light of Zn2+-MQ complexes, and the blue light emission of PVK were synergized. The dual and multi-emission hybrid micelles have great application prospects in ratiometric fluorescent probes and biomarkers.

Electrical and optical properties of organic light-emitting diodes with rhenium(I) complexes using DC and AC methods

Four rhenium(I) tricarbonyl complexes with 1,10-phenanthroline and derivative bearing electron-donating CH3 and OCH3 substituents were doped into host material poly (9-vinylcarbazole) (PVK) with a mass ratio of 8% as the emissive layer in organic light-emitting diodes (OLEDs). All complexes showed photoluminescence in the solution and embedded into a PVK matrix (λmax∼520–550 nm). The comparison with the bare PVK emission and the compound/PVK film shows that the emission of the polymer was quenched through an energy transfer process from PVK to the dopant. The electrical properties of the devices with FTO/PEDOT:PSS/Complex:PVK/Al architecture were investigated using the DC method by curves of current density-voltage and the AC method as admittance spectroscopy, which showed that the behavior of the devices is controlled by charge carrier injection rather than bulk transport.

Facile Preparation of Fluorescent Nanoparticles with Tunable Exciplex Emission and Their Application to Targeted Cellular Imaging

Fluorescent nanoparticles with a tunable emission show a good potential for usage in biological imaging. Exciplex emission usually appears with a large red shift from the normal emission peak. The integration of exciplex emission into nanoparticles offers a rational strategy to designing fluorescent nanoparticles with a tunable emission. In this work, we doped electron acceptors into the electron donor poly(N-vinylcarbazole) (PVK) to develop novel fluorescent nanoparticles with a conveniently modulated PVK emission. Through careful design of the molecular structures of the electron acceptors, we demonstrated that controlled donor–acceptor spatial stacking and electron transitions could regulate the exciplex emission of the PVK/acceptor nanoparticles. Thus, the structurally controlled exciplex formation allowed for the preparation of multicolored fluorescent nanoparticles. Moreover, further modifications with the cyclic peptide RGD showed little disruption to the structure of the PVK/acceptor nanoparticles...

Synthesis, characterization, photophysical and electrochemical properties of fac-tricarbonyl(4,7-dichloro-1,10-phenanthroline)rhenium(I) complexes

The fac-[Re(CO)3Cl(Cl2phen)] and fac-[Re(CO)3(py)(Cl2phen)]PF6 complexes were synthesized, purified and characterized by 1H NMR, UV–Vis and IR spectroscopies and both photophysical and electrochemical behaviors were investigated. The electronic absorption spectra exhibit two main absorption bands: the higher energy band, which was assigned to IL, and the lower energy band, assigned to MLCT. The fac-[ReCl(Cl2phen)(CO)3] and fac-[Re(py)(Cl2phen)(CO)3]PF6 complexes showed emission at room temperature in both CH3CN solution (λmax=640nm, ϕ=0.0027; λmax=590nm, ϕ=0.055) and rigid media (λmax=590nm, λmax=535nm in PMMA) arising from the lowest lying metal to ligand charge transfer (3MLCTRe→Cl2phen) excited state. Additionally, the PVK emission band is almost completely quenched in the presence of 4% rhenium(I) complex. Both compounds showed metal-centered oxidation, Re(I)→(II), and ligand-based reduction, Cl2phen→Cl2phen∗−, in CH2Cl2 solution. The highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energy levels of both complexes were estimated. The electrochemical and emission properties indicate a potential application of the rhenium(I) compounds in OLED devices.

Morphology and photoluminescence properties of electrospun microfibers of poly(9-vinylcarbazole)/tris-(8-hydroxyquinoline)aluminum and poly(9-vinylcarbazole)/4,7-diphenyl-1,10-phenanthroline blends

Green fluorescent electrospun fibers of poly(9-vinylcarbazole) (PVK)/tris-(8-quinolinolato)aluminum (Alq3) and PVK/4,7-diphenyl-1,10-phenanthroline (Bphen) with widths on the micrometer scale were successfully obtained from solutions in dichloroethane (DCE). The concentration of the electron-transport molecules (Alq3 or Bphen) was from 0.5 to 60 (wt%). PVK/Alq3 fibers were thick and rough whereas PVK/Bphen fibers were thin and uniform; additionally, the electrospinnability of the solutions with Bphen was enhanced significantly. Studies of photoluminescence (PL) indicate an efficient energy transfer from PVK to Alq3 in electrospun PVK/Alq3 fibers. As for PVK/Bphen fibers, the consistent decrease of the broad PVK emission is mainly attributed to Bphen favoring the formation of fully overlapping, sandwich-like configurations in the PVK. The parallel decrease of the PLE spectra as Bphen increases corroborates the increment in excimer formation.

Yellow-green electroluminescence of samarium complexes of 8-hydroxyquinoline

Four novel samarium complexes were prepared by reacting samarium(III) nitrate with 8-hydroxyquinoline, 2-methyl-8-hydroxyquinoline, and 1,10-phenanthroline and utilized as emitting materials in the electroluminescence device. All complexes were characterized by elemental analysis, infrared, UV–vis and 1H NMR spectroscopes and the molecular structure of a representative complex, [Sm2(Me-HQ)4(NO3)6] (1), was determined by single-crystal X-ray diffraction. Utilization of a π-conjugated (phenanthroline) ligand as a second ligand in the structure of the samarium complexes resulted in red shifts in both absorption and fluorescence spectra of complexes and moderately enhanced the photoluminescence intensity and the fluorescence quantum yield. The maximum emission peaks showed that a good correlation exists between the nature of the substituent group on the 8-hydroxyquinoline and the addition of the π-conjugated ligand in the structure of samarium complexes and emission wavelength. Devices with samarium(III) complexes with structure of ITO/PEDOT:PSS (90nm)/PVK:PBD:Sm(III) complexes (75nm)/Al (180nm) were fabricated. In the electroluminescence (EL) spectra of the devices, a strong ligand-centered emission and narrow bands arising from the 4G5/2→6HJ transitions (J=7/2, 9/2, and 11/2) of the samarium ion were observed for the complexes. The electroluminescent spectra of the samarium complexes were red-shifted as compared with the PVK:PBD blend. We believe that the electroluminescence performance of OLED devices based on samarium complexes relies on overlaps between the absorption of the samarium compounds and the emission of PVK:PBD. This revealed that it is possible to evaluate the electroluminescence performance of the samarium compounds-doped OLED devices based on the emission of PVK:PBD and the absorption of the dopants.

White light electroluminescence from poly(9-vinylcarbazole) (PVK)/ZnO NRs/poly(2-methoxy-5-(2-ethylhexyloxy)-1, 4-phenylenevinylene) (MEH-PPV) dual heterojunctions

In this paper, we fabricated a p-PVK/n-ZnO nanorods (NRs)/p-MEH-PPV dual heterojunctions white light-emitting diode. Relative to previously reported p–n heterojunction structure including ZnO NRs and polymer, the device exhibits a low turn-on voltage of 7 V. An obviously broad electroluminescence emission band, originated from the overlap of PVK emission and ZnO defects emissions, was observed extending from 360 up to 700 nm. The influence of the two introduced p-type polymer layers on the device characteristic is discussed. With its hole conductivity, the p-PVK layer cannot only improve the holes tunnel into ZnO NRs layer, but also lower the barrier between ITO and the valance band of ZnO NRs. On the other hand, p-MEH-PPV could be regarded as block layer for the injection of electrons from the Al electrode. Both of two p-type polymers dramatically improve the injection balance of carriers, leading to a low turn-on voltage. Meanwhile, the carrier transport mechanism of the device under different forward bias region was discussed on the basis of current–voltage curve.

Yellow–Orange Electroluminescence of Novel Tin Complexes

Novel tin complexes were synthesized for use as fluorescent materials in organic light-emitting diodes (OLEDs). The structures of these complexes were characterized by ultraviolet–visible, Fourier-transform infrared, and nuclear magnetic resonance spectroscopy methods and elemental analyses. The energy levels of the tin complexes were determined using cyclic voltammetry measurements. Devices were fabricated with an indium tin oxide (ITO)/PEDOT:PSS (90 nm)/PVK:PBD:tin complexes (75 nm)/Al (180 nm) structure; the resultant devices had peak emissions ranging from 537 nm to 580 nm. The tin complexes accounted for 8 wt.% of the blend in the PVK:PBD (100:40), which was used as a host. The electroluminescent spectra of the tin complexes were red-shifted as compared with the PVK:PBD blend. We believe that the electroluminescence performance of OLED devices based on tin complexes relies on overlaps between the absorption of the tin compounds and the emission of PVK:PBD.

Multi-colour emission from dye doped polymeric nanotubes by host–guest energy transfer

Emission chromaticity tuning in polymeric nanotubes was achieved by transfer of excitation energy from a polymer host matrix poly(N-vinylcarbazole) (PVK) to incorporated luminescent chromophore guests (Coumarin 6 and Nile red). Nanotubes were synthesized in densely packed arrays by solution assisted template wetting. Un-doped PVK tubes displayed blue luminescence while Coumarin 6 and Nile red doped tubes exhibited characteristic green and red luminescence with minimal PVK emission, confirming effective host–guest energy transfer. The emission spectral data of single nanotubes, and indicated that, by varying the type and relative concentrations of the dopant dyes, nanotube emission could be tuned from the blue, through green and yellow, to the red and, ultimately, to white, while maintaining excellent color purity.

Synthesis and characterization of the europium (III) complex as an organic luminescent material

The red emission organic material Eu(coumarin)3·2H2O complex was synthesized and its morphology, energy level alignment and luminescence characteristics were studied by using scanning electron microscopy, Fourier transform infrared spectra, cyclic voltammetry and ultraviolet–visible absorption spectra and fluorescence spectra. Eu(coumarin)3·2H2O shows bright red emission originating from Eu3+ ions under 345 nm light excitation. The luminescence lifetime of Eu3+ in this complex is about 580 μs. To improve the quality of Eu(coumarin)3·2H2O thin films, Eu(coumarin)3·2H2O was doped with a poly(N-vinylcarbazole) (PVK) solution. The organic materials 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) and aluminum quinoline (Alq3) were used as hole-blocking and electron-transporting layers in our fabricated electroluminescence (EL) devices on indium tin oxide (ITO) substrates, respectively. The EL devices ITO/poly-(3,4-ethylenedioxythiophene):poly-(styrenesulphonic acid) (PEDOT:PSS)/emitting layer (PVK:Eu)/BCP/Alq3/Al were fabricated, and EL spectra were measured under different driving voltages. There is one emission peaking at 490 nm in addition to the characteristic emission peaks of Eu3+, which should be attributed to the spectral overlap between the PVK emission and electroplex emission originating from PVK and BCP interfaces. This explanation can be positively supported by the dependence of the EL spectral variation of ITO/ PVK/BCP/Alq3/Al devices on the driving voltage.

White Emission via Electroplex Emission from Two Blue Materials

Influences of electric fields on the emission from organic light-emitting diodes (OLEDs) based on poly (N-vinylcarbazole) (PVK); 2, 9-dimethyl-4, 7-diphenyl-1, 10-phenanthroline (BCP); and tris (8-hydroxyquinoline) aluminum (Alq3) were studied. There are three emission peaks at 420 nm, 520 nm, and 620 nm of the device ITO/PEDOT: PSS/PVK/BCP/LiF/Al under different driving voltages. The emissions at 420 nm and 520 nm should be from the exciton emission of PVK and Alq3, respectively. The last emission at 620 nm could be attributed to electroplex emission at the interface between the PVK and BCP layers. A high intensity white emission via electroplex formation was obtained with Commission International d'Eclairage (CIE) coordinates (0.33, 0.34) at 15 V, which is very close to the equienergy white point (0.33, 0.33).

Enhanced pure red electroluminescence intensity of Eu(o-BBA)3(phen) by red dye co-doping and inorganic semiconductor as charge carrier function layer

There is an emission peak at 494nm in the electroluminescence (EL) of PVK [poly(n-vinylcarbazole)]: Eu(o-BBA)3(phen) besides PVK exciton emission and Eu3+ characteristic emissions. Both the peaking at 494nm emission and PVK emission influenced the color purity of red emission from Eu(o-BBA)3(phen). In order to restrain these emissions and obtain high intensity red emission, 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7,-tetramethyljulolidy-9-enyl)-4Hpyran (DCJTB) and Eu(o-BBA)3(phen) were co-doped in PVK solution and used as the active emission layer. The EL intensity of co-doped devices reached to 420cd/m2 at 20V driving voltage. The chromaticity coordinates of EL was invariable (x=0.55, y=0.36) with the increase of driving voltage. For further improvement of EL intensity, organic–inorganic hybrid devices (ITO/active emission layer/ZnS/Al) were fabricated. The EL intensity was increased by a factor of 2.5 [(420cd/m2)/(168cd/m2)] when the Eu complex was doped with an efficient dye DCJTB, and by a factor of ≈4 [(650cd/m2)/(168cd/m2)] when in addition ZnS layer was deposited on such an emitting layer prior to evaporation of the Al cathode.

The effect of DCJTB doping concentration in PVK on the chromatic coordinate of electroluminescence

The dominant mechanism of electroluminescence (EL) from 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) doped in poly-(N-vinyl-carbazole) (PVK) system was demonstrated to be a charge carrier trapped by DCJTB molecular rather than Förster energy transfer from PVK to DCJTB. The chromatically coordinate EL emission of PVK:DCJTB changes from (0.41, 0.31) to (0.67, 0.31) with an increase in DCJTB doping concentration. The emission peak in DCJTB shows red-shift and the shoulder emission peak at 656 nm becomes stronger as the doping concentration increases. The effect of DCJTB doping concentration on EL spectra is attributed to strong dipole–dipole interaction between the DCJTB molecule with an increase in doping concentration.

Study of photoluminescence and energy transfer properties of an organic dye salt doped thin films

The photoluminescence and energy transfer properties based on an organic salt trans-4-［p-(N-ethyl-N-(hydroxylethyl)amino)phenylstyryl］-N-(hydroxyethyl)pyridinium iodide (ASPI) doped PVK thin film were investigated by steady-state and time-resolved fluorescent spectra. We observed that the emission intensity and the fluorescent lifetime of PVK reduced with increasing ASPI doping concentration due to the Forster energy transfer from PVK to ASPI, which is strongly correlated with an efficient spectral overlap between ASPI absorption and PVK emission. We also added some Alq3 into the doping system as energy carriers in order to increase the energy transfer efficiency from PVK to ASPI at low concentration, or there will be an evident decrease in photoemission efficiency due to the concentration quenching at high concentration. The dynamical process of energy transfer is discussed.

Study on Luminescence Properties of a Novel Rare Earth Complex Eu(TTA) 2 (N-HPA)Phen

A novel rare earth complex Eu (TTA) 2(N-HPA) Phen (TTA = thenoyltrifluoroacetone, N-HPA = N-pheny-lanthranilic acid, and phen = 1, 10-phenathroline), which contains three different ligands, was synthesized. The Eu complex was blended with poly N-vinylcarbazole (PVK) in different weight ratios and spin coated into films. The luminescence properties of films were investigated and energy transfer between PVK and the complex was discussed. Multilayer structural devices consisting of ITO/PVK: Eu(TTA) 2(N-HPA) phen/BCP/Alq 3/Al were fabricated with PVK: Eu (TTA) 2(N-HPA) as light-emitting layer. Increasing the concentration of Eu in the PVK thin film would inhibit the emission of PVK to different degrees. Finally, the pure red luminescence of europium (III) was observed when the doping weight ratio was approximately 1:5, which indicated an effective energy transfer from PVK to rare earth complex.

Electroplex emission from bi-layer blue emitting organic materials

Electroluminescence (EL) and photoluminescence (PL) spectra of an electron donor, an (poly(N-vinylcarbazole) (PVK))/electron acceptor, and a (2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD)) bi-layer solid film are analysed. The EL emission peak has an apparent red-shift with the increase of driving voltage. There maybe exist an electroplex emission between the PVK and PBD interface under high electric field strength. According to their energy level, the electroplex emission peak should locate at 460 nm. There are great spectra overlapping between PVK emission and electroplex emission, and the ratio of electroplex emission intensity to exciton emission intensity (Ielectroplex/Iexciton) increases from 0.38 at 10 to 0.81 at 16 V. Therefore the measured emission peaks continuously shift from 410 nm at 10 V to 445 nm at 16 V.

Organic light-emitting devices based on new rare earth complex Tb(p-CIBA)3phen

A new rare earth complex Tb(p-CIBA)3phen was synthesized and introduced into organic light emitting devices (OLEDs) as emitting material. The Tb(p-CIBA)3phen was doped into PVK to improve the film-forming and hole-transporting property. Two kinds of devices were fabricated. The device structure is as the following. Single-layer device: ITO/PVK: Tb(p-CIBA)3phen/LiF/Al; double-layer device: ITO/PVK: Tb(p-CIBA)3phen/AIQ/LiF/Al. The performances of both devices were investigated carefully. We found that the emission of PVK was completely restrained, and only the green emission was observed from the electroluminescence. The full width at half maximum (FWHM) was less than 10 nm. The highest EL brightness of the single-layer device is 25.4 cd/cm2 at a fixed bias of 18 V, and the highest EL brightness of the double-layer device reaches 234.8 cd/cm2 at a voltage of 20 V.

Emission characteristics of Tb( o-MBA) 3phen doped in PVK system

A rare-earth complex Tb ( o-MBA) 3phen has been synthesized and used as an emitting material in electroluminescence. By doping it into the conjugated polymer PVK, devices with different structures were fabricated: Device A: Glass/ITO/PVK: Tb( o-MBA) 3phen /LiF/Al; Device B: Glass/ITO/PVK: Tb( o-MBA) 3phen/AlQ/LiF/Al; Device C: Glass/ITO/PVK: Tb( o-MBA) 3phen/BCP/AlQ/LiF/Al. The characteristics of these devices were investigated. For single-layer and double-layer devices, the emission of PVK was completely restrained, and only the green emission from Tb 3+ can be observed in electroluminescence. It is because of the different mechanism of electroluminescence and photoluminescence. In photoluminescence process, the energy of Tb complex may come from PVK through Förster energy transfer process, and in electroluminescence process direct sequential charge trapping appeared to be the main operating mechanism. From the optimized device B, bright green emission can be obtained, and the highest EL brightness of the device reached 180 cd/m 2 at 15 V.

Emission Characteristics of PVK Doped TbY(o-MBA) 6(phen) 2 Systems

A rare earth complex TbY (o-MBA) 6(phen) 2 was synthesized, which was first used as an emitting material in electroluminescence. By doping it into the conjugated polymer PVK, single-layer and double-layer devices were fabricated with structures: device A: ITO/PVK: TbY (o-MBA) 6(phen) 2/BCP/Al; B: ITO/PVK: TbY (o-MBA) 6(phen) 2/AlQ/LiF/Al; C: ITO/PVK: TbY (o-MBA) 6(phen) 2/BCP/AlQ/LiF/Al. The characteristics of these devices were investigated. For single-layer and double-layer devices, the emission of PVK was completely restrained, and only the green emission from Tb 3+ was observed in electroluminescence. The above mentioned observation is attributed to the different mechanism of electroluminescence and photoluminescence. In photoluminescence process, the energy of Tb complex may come from PVK through Förster energy transfer process, while in electroluminescence process direct sequential charge trapping appeares to be the main operating mechanism. From the optimized device B, brightly green emission can be obtained, and the highest EL brightness of the device reaches 213 cd·m −2 at 14 V.

Miscibility effect on the energy transfer induced luminescence enhancement of polyimide/PVK blends

Two series of polyimides exhibiting red light luminescence were synthesized. The energy transfer between poly( N-vinylcarbazole) (PVK) and polyimide enhances the red light luminescence of the polyimide. Meanwhile, the purplish blue light luminescence of the pure PVK polymer was not or hardly observed in the light luminescence spectra of the polyimide/PVK blend depending on the composition of the blend. There was more spectral overlap between the PL emission of PVK and the absorption of the pyromellitic dianhydride (PMDA)–2,7-diaminofluorene (DAF) polyimide than that of the PMDA–3.7-diamino-2.8-dimethyldibenzo-thiophene sulfone (DAS) polyimide. Therefore, the PMDA–DAF polyimide/PVK blends that showed complete energy transfer exhibited the emission spectrum mostly from the polyimide. Incorporating a modified silicone surfactant further showed remarkable enhancement of the red luminescence by improving the miscibility of the blends of PMDA–DAF polyimide with PVK.