Efficient Blue Fluorescence Research Articles

Quantifying the Energy Loss of Triplet Excitons on High‐Lying Triplet States to Develop High Efficiency Blue Fluorescence OLEDs Based on AIE Emitter

Abstract“Hot exciton” molecules that allow the transition of excitons from a high‐lying triplet state (Tn, n≥ 2) to singlet states (Sm, m≥1) by a reverse intersystem crossing (hRISC) process have become an effective strategy to achieve high efficiency fluorescence organic light emitting diodes (OLEDs). However, the understanding of the dynamic behavior of the “hot exciton” process is still very lacking. Herein, the exciton dynamics of an aggregation‐induced emission (AIE) molecule TPA‐An‐mPhCz with the “hot exciton” property are deeply investigated, and the proportion between hRISC and internal inversion (IC) of excitons on Tn is successfully quantified by in situ transient electroluminescent measurements and theoretical calculation. It is found that the IC process increases severe energy loss of Tn excitons. By introducing a triplet–triplet annihilation up‐conversion layer in the emissive layer to efficiently recapture the IC excitons and further doping a blue fluorescent emitter in the TPA‐An‐mPhCz layer to achieve high photoluminescence quantum yield (PLQY), the resulting OLED achieves a maximum external quantum efficiency of 12.5% with negligible efficiency roll‐off. More impressively, the operational lifetime LT75 (lifetime to 75% of the initial luminance) of the device with efficient triplets utilization performs a remarkable 116 h under 1000 cd m−2. This work provides the fundamentals for the design of hot exciton materials with efficient exciton utilization to develop efficient blue fluorescence OLEDs.

Efficient blue fluorescence tandem organic light emitting device with a novel intermediate connector

A novel intermediate connector (IC) was formed which was composed of aluminum (Al, 3 nm)/1,4,5,8,9,11-hexaazatriphenylene-hexacarbonitrile (HAT-CN). The 3-nm-thick Al in the IC is certified to efficiently generate intrinsic charge carriers, and the HAT-CN is proved to work as the holes injection layer (HIL) for the corresponding electroluminescent (EL) unit simultaneously. This simply IC comprehensively takes advantage of the features of the HAT-CN so as to stack two single EL units without introducing extra material. In addition to a significant enhancement in luminance and current efficiency, a current efficiency (CE) of 10.2 cd/A and a luminance of 2 042 cd/m2 under the current density 20 mA/cm2 of this tandem organic light emitting device (TOLED) are yielded, which are notably almost the sum of that of the two single-unit devices.

Synthesis and application of the blue fluorescent amino acid l-4-cyanotryptophan to assess peptide-membrane interactions.

Recently, l-4-cyanotryptophan has been shown to be an efficient blue fluorescence emitter, with the potential to enable novel applications in biological spectroscopy and microscopy. However, lack of facile synthetic routes to this unnatural amino acid limits its wide use. Herein, we describe an expedient approach to synthesize Fmoc protected l-4-cyanotryptophan with high optical purity (>99%). Additionally, we test the utility of this blue fluorophore in imaging cell-membrane-bound peptides and in determining peptide-membrane binding constants.

Rhodium-Catalyzed Cascade Synthesis of Benzofuranylmethylidene-Benzoxasiloles: Elucidating Reaction Mechanism and Efficient Solid-State Fluorescence.

A new synthetic route to highly fluorescent benzofuranylmethylidenebenzoxasiloles through cationic rhodium(I)/binap complex-catalyzed cascade cycloisomerization of bis(2-ethynylphenol)silanes has been developed involving 1,2-silicon and 1,3-carbon (alkyne) migrations followed by oxycyclization. The present synthesis requires only three steps, starting from commercially available dichlorodiisopropylsilane, which is markedly shorter than our previous synthesis (eight steps starting from commercially available chlorodiisopropylsilane). Theoretical calculations elucidated the mechanism of the above cascade cycloisomerization. This reaction is initiated by the formation of a rhodium vinylidene not through direct 1,2-silicon migration but rather through an unprecedented stepwise 1,5-silicon migration followed by C-Si bond-forming cyclization from a dearomatized allenylrhodium complex. Subsequent 1,3-carbon (alkyne) migration leading to a η3 -allenyl/propargyl-rhodium complex followed by oxycyclization through π-bond (alkyne) activation with the cationic rhodium(I) complex affords the benzofuranylmethylidenebenzoxasilole product. The structure-fluorescence property relationships of the thus obtained benzofuranylmethylidenebenzoxasiloles were investigated, which revealed that good fluorescence quantum yields were generated in the solution state (φF =69-87 %) by introduction of electron-donating alkyl and phenyl groups on two phenoxy groups. In the powder state, 4-methyl- and 4-methoxy-phenoxy derivatives exhibited efficient blue fluorescence (φF =52 % and 46 %, respectively). Especially, the 4-methylphenoxy derivative was thermally stable, and exhibited strong narrow-band fluorescence in the film state (blue, φF =95 %) and redshifted strong narrow-band fluorescence (green, φF =90 %) in the crystalline state as a result of the formation of an offset π-stacked dimer; the latter was confirmed by X-ray crystallographic analysis and by theoretical calculations.

Enhanced Photoluminescence of Mesostructured Organosilica Films with a High Density of Fluorescent Chromophores

AbstractSynthesis of mesostructured materials containing a high density of organic chromophores in the frameworks is highly desired for applications in unique optical devices using energy transfer. However, a dense accumulation of fluorescent chromophores in solid form generally causes concentration quenching. In this study, dense embedding of the chromophore 1,6‐diphenylpyrene within the framework of mesostructured organosilica films results in efficient blue fluorescence emission with high quantum yields of over 0.75. In contrast to conventional fluorescent films where chromophores are diluted and isolated to suppress concentration quenching, increasing the density of 1,6‐diphenylpyrene moieties within the mesostructured framework leads to the efficient formation of highly emissive excimers. Mesostructured frameworks achieving both high light‐absorptivity and efficient fluorescence emission have great potential in light‐emitting materials, fluorescence sensors, and light‐harvesting components for photoluminescent and photocatalytic systems.

Quantification of excitation-power dependency in Tm3 +/Yb3 + doped fluorotellurite upconverting glass phosphor for iris recognition

Excitation-power dependency of upconversion (UC) photons have been quantified in Tm3+/Yb3+ doped fluorotellurite (BALMT) glasses under the excitation of 975nm laser. The net powers of three-photon-excited blue and red and two-photon-excited NIR emissions are determined to be 242, 101 and 7994μW in 0.5wt% Tm2O3 and 2wt% Yb2O3 co-doping case under the excitation power of 870mW, respectively, and the net emission photon numbers are identified to be 58.2×1013, 33.0×1013 and 3253.2×1013cps. The quantum yields (QYs) for multi-photon-excited UC emissions of Tm3+ are identified as a positive dependency with pumping powers, and the relativity for three-photon fluorescence is extremely severe. When the excitation power density is set to 110.8W/mm2, the QY values for 476nm blue and 650nm red UC emissions are up to 1.49×10−4 and 0.84×10−4, and furthermore, the value for 809nm NIR UC emission is as high as 83.22×10−4. The 809nm luminescence is one of the good matching wavelengths for iris recognition in NIR ranges, the intensive NIR luminescence and the efficient blue fluorescence are promising in scanning and positioning for iris scanning. The macroscopic quantization for UC photon generation from Tm3+ in low-phonon fluorotellurite glasses provides a reliable reference for developing compact high-power-density light sources in iris recognition.

Introduction of Twisted Backbone: A New Strategy to Achieve Efficient Blue Fluorescence Emitter with Delayed Emission

By introducing an acceptor which contains double sulfonyl groups and a twisted biphenyl core, an efficient blue thermally activated delayed fluorescence emitter is successfully developed. Comparative study and analysis are carried out on it with an analogous molecule, which also imports two sulfonyl groups as acceptors and exactly same donor units but shows stretched shape and displays green emission. Results of quantum chemistry computation estimate that the introduction of such a twisted backbone is beneficial to increase energies of both singlet and triplet states. As a contrast to its counterpart, the newly developed blue emission compound with contorted structure enables a desirable emission with a peak wavelength of 460 nm and superior photoluminescence quantum yield up to 82%. Moreover, remarkable external quantum efficiency over 24% and Commission International de l'Eclairage coordinates with total (x + y) value <0.4 are achieved from the electroluminescent device based on the blue emitter, while this value is almost twice to that of the green emission device based on its analog.

Blade coating of Tris(8-hydroxyquinolinato)aluminum as the electron-transport layer for all-solution blue fluorescent organic light-emitting diodes

Organic light-emitting diodes (OLEDs) with a low driving voltage and efficient blue fluorescence were fabricated through blade coating. Tris(8-hydroxyquinolinato)aluminum (Alq3) is a relatively stable electron-transporting material commonly used in evaporation. However, depositing Alq3 through a solution process is difficult because of its extremely low solubility organic solvents, a result of its symmetrical molecular structure. In this study, Alq3 was successfully deposited through blade coating at a very low concentration below 0.1wt%. The OLEDs contained co-dopants BUBD-1 and p-bis(p-N,N-diphenyl-aminostyryl)benzene (DSA-Ph), and a high-band-gap host 2-methyl-9,10-bis(naphthalen-2-yl)anthracene (MADN) as the emission layer with the following structure: ITO/PEDOT:PSS (40 nm)/VB-FNPD (30 nm)/MADN:2% BUBD-1:1% DSA-Ph (50 nm)/TPBI (30 nm)/LiF (0.8 nm)/Al (100 nm)or ITO/PEDOT:PSS (40 nm)/VB-FNPD (30 nm)/MADN:3% BUBD-1 (50 nm)tris(8-hydroxyquinolinato)aluminum (Alq3; 10 nm)/LiF (0.8 nm)/Al (100 nm). 2,7-disubstituted fluorene-based triaryldiamine(VB-FNPD)is the cross-linking transporting material. The device exhibited a peak current efficiency of 5.67 cd/A for Alq3 and 5.76 cd/A for TPBI. The device with Alq3 has operated lifetime seven times higher than the device with TPBI.

White organic light-emitting diodes based on a yellow phosphorescence iridium complex and a high-efficiency blue fluorescence

We have demonstrated white organic light-emitting diodes (WOLEDs) based on a yellow phosphorescence iridium complex and an efficient blue fluorescence. The property of the blue fluorescence is studied and the pure blue device can obtain a peak current efficiency (CE) of 8.5cd/A. The best obtained WOLED shows a peak CE of 24.7cd/A at 1000cd/m2 with Commission Internationale De L'Eclairage coordinate of (0.44, 0.48), while WOLEDs based on different architectures exhibit good color stability.

Novel Efficient Blue Fluorophors with Small Singlet‐Triplet Splitting: Hosts for Highly Efficient Fluorescence and Phosphorescence Hybrid WOLEDs with Simplified Structure

The exact hosts for F-P hybrid WOLEDs have been first demonstrated following a new design strategy for blue fluorophors with small singlet-triplet splitting. Two novel compounds DPMC and DAPSF exhibit efficient blue fluorescence, high triplet energies and good conductivities. These merits allow us to use new simplified device designs to achieve high efficiency, slow efficiency roll-off and stable emission color.

Conjugated Polyelectrolyte Dendrimers: Aggregation, Photophysics, and Amplified Quenching

Conjugated polyelectrolyte dendrimers (CPDs) are monodisperse macromolecules that feature a fully π-conjugated dendrimer core surrounded on the periphery by ionic solubilizing groups. CPDs are soluble in water and polar organic solvents, and they exhibit photophysics characteristic of the π-conjugated chromophores comprising the dendrimer core. Here we describe the synthesis and photophysical characterization of series of three generations of CPDs based on a phenylene ethynylene repeat unit structure that is surrounded by an array of anionic sodium carboxylate groups. Molecular dynamics simulations indicate that the first-generation CPD is flat while the second- and third-generation CPDs adopt oblate structures. Photophysical studies, including absorption, fluorescence spectroscopy, and lifetimes, show that the ester protected precursor dendrimers exhibit highly efficient blue fluorescence in THF solution emanating from the phenylene ethynylene chromophore that is in the dendrimer core. By contrast, the water-soluble CPDs have much lower fluorescence quantum yields and the absorption and fluorescence spectra exhibit features of strong chromophore-chromophore interactions. The results are interpreted as suggesting that the CPDs exist as dimer or multimer aggregates, even in very dilute solution. Fluorescence quenching of the anionic CPDs with the dication electron acceptor N,N'-dimethylviologen (MV(2+)) is very efficient, with Stern-Volmer quenching constants (K(SV)) increasing with generation number. The third-generation CPD exhibits highly efficient amplified quenching, with K(SV) ∼ 5 × 10(6) M(-1).

Multifunctional electron-transporting indolizine derivatives for highly efficient blue fluorescence, orange phosphorescence host and two-color based white OLEDs

In this work, derivatives of indolizine are first used as electron-transporting host materials for hybrid fluorescence/phosphorescence white organic light-emitting devices (F/P-WOLED). Of the indolizine derivatives, a blue fluorescent material BPPI (3-(4,4′-biphenyl)-2-diphenylindolizine) was found to have: (1) blue emission with high quantum yields, (2) good morphological and thermal stabilities, (3) electron-transporting properties, and (4) a sufficiently high triplet energy level to act as a host for red or yellow-orange phosphorescent dopants. The multifunctional BPPI enables adaptation of several simplified device configurations. For example, a non-doped blue fluorescent device exhibits good performance with an external quantum efficiency of 3.16% and Commission Internationale de l'Eclairage coordinates of (0.15, 0.07). A high-performance orange phosphorescent device was found to have a high current efficiency of 23.9 cd A−1. Using BPPI, we also demonstrate a F/P-WOLED with a simplified structure, stable emissions and respectable performance (current and external quantum efficiencies of 17.8 cd A−1 and 10.7%, respectively).

Highly Efficient Blue Fluorescence from 3,2′-Silylene-Bridged 2-Phenylindoles in the Solid State

3,2′-Silylene-bridged 2-phenylindoles were prepared in high yields by palladium-catalyzed silicon-migrative intramolecular coupling of 2-(2-indolylsilyl)aryl triflates. The high thermal stability of the benzosilole-fused indoles was indicated by thermogravimetric analysis (TGA). The absorption spectra revealed that the absorption edges, namely, the HOMO–LUMO energy gaps, could be effectively tuned by substitution with functional groups such as chloro, cyano, methoxy, and phenyl at the meta-positions with respect to nitrogen and silicon, whereas there was no effective conjugation between the core and an aryl group on nitrogen. The changes in the HOMO–LUMO gaps, which were induced by variation of the functional groups, were well reproduced by density functional theory calculation. The indoles exhibited blue fluorescence with high-to-excellent quantum yields both in cyclohexane and in powder as well as in doped poly(methyl methacrylate) (PMMA) films. The emission maxima of each indole exhibited a red-shift, ...

Synthesis and Characterization of a New Series of Blue Fluorescent 2,6-Linked 9,10-Diphenylanthrylenephenylene Copolymers and Their Application for Polymer Light-Emitting Diodes

A series of new 9,10-diphenylanthracene-based, 2,6-linked blue-light-emitting copolymers bearing hole- or electron-transporter as well as bulky substituent were successfully synthesized. Photophysical, thermal, electrochemical, and electroluminescence (EL) properties of these copolymers were studied and characterized. Bright and efficient blue fluorescence in the solid state was achieved by incorporating bulky substituent into the copolymer backbone. Both hole- and electron-transport-substituted copolymers apparently enhanced the electroluminescent performance of their polymeric light-emitting diodes (PLEDs). A diphenylvinyl-bearing copolymer (pDPV) PLED exhibited sky-blue EL (λmaxEL = 473 nm, CIEx,y = 0.16, 0.28) with peak luminous efficiency of 2.21 cd/A; a N-carbazole bearing copolymer (pCBZ) PLED displayed a blue EL (λmaxEL = 469 nm, CIEx,y = 0.15, 0.22) with peak luminous efficiency of 2.15 cd/A. OXD-7 (1,3-bis(2-(4-tert-butylphenyl)-1,3,4-oxadiazol-5-yl)benzene) as an electron-transporting dopant wa...

Palladium-Catalyzed Intramolecular Coupling of 2-[(2-Pyrrolyl)silyl]aryl Triflates through 1,2-Silicon Migration

Palladium-catalyzed intramolecular direct arylation of 2-[(2-pyrrolyl)silyl]aryl triflates gives 3,2'-silicon-bridged 2-arylindoles and -pyrroles in good to high yields. The reaction proceeds through cleavage of C-OTf, C-Si, and C-H bonds to result in the formation of C-C and C-Si bonds. Various kinds of functional groups such as OMe, CN, Cl, F, and SiMe(3) tolerated the conditions. The new reaction allows synthesis of functionalized Si-bridged 2-arylindoles that emit intense and efficient blue fluorescence in the solid state.

Multifunctional bipolar triphenylamine/oxadiazole derivatives: highly efficient blue fluorescence, red phosphorescence host and two-color based white OLEDs

Two simple triphenylamine/oxadiazole derivatives were synthesized and fully characterized; their multifunctionality as highly efficient non-doped blue fluorescence, excellent red phosphorescent host and single-doped two-color based white OLEDs has been demonstrated.

Cerium-bound excitions and fluorescence quenching effects in cerium doped LaLuO3 single crystals

A new cerium-doped crystal has been grown and its fluorescence properties have been investigated through laser and synchrotron spectroscopies. While the crystal exhibits an efficient blue fluorescence when excited in the near UV absorption bands, its fluorescence is strongly quenched when excited in the fundamental absorption regions. This phenomenon is interpreted by a model involving the formation of cerium-bound excitons, their lowest excited state lying closely in energy from the emitting state of Ce3+. The role played by the 4f level of lutetium in the scintillation efficiency of cerium-doped lutetium-based oxide crystals is discussed through the comparison of both systems LaLuO3 : Ce and LuAlO3 : Ce.

Synthesis of a functional polymer with pendent luminescent phenylenevinylene units through nitroxide‐mediated free‐radical polymerization

AbstractIn this communication we report the synthesis and the efficient polymerization of a PPV trimer, 4‐tert‐buty1‐4′‐(4‐vinylstyryl)‐trans‐stilbene. By using the TEMPO (2,2,6,6‐tetramethylpiperidin‐1‐yloxy)‐mediated free‐radical polymerization method, the corresponding polymer was obtained in high yields, with a fair molecular weight and a small polydispersity. The presence of phenylenevinylene units in the side chains of the polymer gives rise to efficient blue fluorescence which makes the material suitable for light emission applications.