Blue Fluorophore Research Articles

Novel "hot exciton" blue fluorophores for high performance fluorescent/phosphorescent hybrid white organic light-emitting diodes with superhigh phosphorescent dopant concentration and improved efficiency roll-off.

Two blue fluorophores with excellent hybridized local and charge-transfer (HLCT) and "hot exciton" properties were developed as the blue emitter and the host for orange-red phosphor to achieve highly efficient fluorescent/phosphorescent (F/P) hybrid white organic light-emitting diodes (WOLEDs) in a single-emissive-layer single-dopant (SEML-SD) architecture even at a high concentration of phosphorescent dopant. In the devices, part of the triplet excitons of the blue fluorophores can be utilized to realize reverse intersystem crossing from the triplet excited states to the singlet excited states for blue emission, and the diffusion volume range of the triplet excitons is reduced significantly. When the phosphorescent dopant concentration is up to 1.0 wt %, which is ten times higher than the traditional single-EML-SD F/P hybrid WOLEDs, highly efficient white emission was still achieved with maximum total external quantum efficiency (EQE) of 23.8%, current efficiency (CE) of 56.1 cd A(-1), and power efficiency (PE) of 62.9 lm W(1-). The results will supply a novel method for obtaining high efficiency F/P hybrid WOLEDs in a SEML-SD architecture with easily controllable doping concentration.

Highly efficient hybrid warm white organic light-emitting diodes using a blue thermally activated delayed fluorescence emitter: exploiting the external heavy-atom effect

To attain high efficiencies in hybrid white organic light-emitting diodes (WOLEDs), mutual quenching of the fluorophors and phosphors should be minimized. Efforts have been devoted to reducing the triplet quenching of phosphors; however, the quenching of fluorophors by the external heavy-atom effect (EHA) introduced by the phosphors is often ignored. Here, we observed that conventional fluorophors and fluorophors with thermally activated delayed fluorescence (TADF) behave differently in the presence of EHA perturbers. The efficiencies of the conventional fluorophors suffer greatly from the EHA, whereas the TADF fluorophors exhibit negligible changes, which makes TADF materials ideal fluorophors for hybrid devices. WOLEDs using a blue TADF fluorophor and an orange phosphor achieve a maximum forward viewing external quantum efficiency of 19.6% and a maximum forward viewing power efficiency of 50.2 lm W−1, among the best values for hybrid WOLEDs. This report is the first time that the EHA effect has been considered in hybrid WOLEDs and that a general strategy toward highly efficient hybrid WOLEDs with simple structures is proposed. Warm white organic light-emitting diodes with a power efficiency of up to 85.3 lm W–1 are reported by scientists in China. The emitters fabricated by Dongdong Zhang and co-workers from Tsinghua University in Beijing are based on the use of a yellow phosphor (PO-01) and a blue fluorophore (2CzPN), which exhibits thermally activated delayed fluorescence (TADF). The device operates with a total external quantum efficiency of 33.3%. The team says that such high efficiency is made possible by the minimizing the fluorescence quenching processes that can occur between the phosphor and the fluorophore. In particular, their TADF fluorophore is shown to be highly robust against quenching resulting from external heavy atom effects introduced by metal phosphors. The approach could lead to a simpler design of white emitters.

A high-efficiency hybrid white organic light-emitting diode enabled by a new blue fluorophor

High-efficiency hybrid white organic light-emitting diode enabled by a new blue fluorophor.

Deep blue fluorophores incorporating sulfone-locked triphenylamine: the key for highly efficient fluorescence–phosphorescence hybrid white OLEDs with simplified structure

Deep blue fluorophors incorporating sulfone-locked triphenylamine were developed for hybrid white OLEDs.

Highly efficient single- and multi-emission-layer fluorescent/phosphorescent hybrid white organic light-emitting diodes with ∼20% external quantum efficiency

A blue fluorophore BBPI was utilized to fabricate fluorescent/phosphorescent hybrid WOLEDs with ∼20% external quantum efficiency.

A novel nicotinonitrile derivative as an excellent multifunctional blue fluorophore for highly efficient hybrid white organic light-emitting devices

A multifunctional compound that serves as both an efficient blue fluorescent emitter and a high performance host for various phosphors simultaneously.

Nitroreductase-triggered activation of a novel caged fluorescent probe obtained from methylene blue.

A near-infrared fluorescent probe based on methylene blue (p-NBMB) was developed for the detection of nitroreductase. Conjugating methylene blue with a p-nitrobenzyl moiety enables it to be activated by nitroreductase-catalyzed 1,6-elimination, resulting in the release of an active methylene blue fluorophore.

Design and Characterization of 4,5‐Bis(diarylamino)phthalic Acid Diesters as a New Class of Fluorophores Exhibiting Efficient Blue Emission in the Solid State

AbstractWe developed 4,5‐bis(diarylamino)phthalic acid diesters as blue fluorophores exhibiting efficient photoluminescence in powder and in a thin film of pol(methyl methacrylate). Increasing the electron‐donating nature of the substituents in the para positions of the diarylamino moieties in the dimethyl esters increased the redshift in the fluorescence spectrum. Replacing the methoxycarbonyl groups with aryloxylcarbonyl groups also induced a bathochromic shift in the fluorescence spectrum. Thus, the color of the emission was finely tuned by simple molecular modification. Single‐crystal X‐ray analysis revealed a twisted conformation with loose packing in the crystal. Density functional theory calculations suggested that the excitation process was governed by intramolecular charge transfer from the diarylamino moieties to the alkoxycarbonyl groups.

Blue Aggregation‐Induced Emission Luminogens: High External Quantum Efficiencies Up to 3.99% in LED Device, and Restriction of the Conjugation Length through Rational Molecular Design

Great efforts have been devoted to seek novel approaches for constructing blue fluorescent materials, which is one of the most important prerequisites for the commercialization of OLEDs. In recent years, various outstanding luminogens with aggregation‐induced emission characteristic exhibit promising applications as emitters, but blue AIE fluorophores with excellent EL performance are still very scarce. Here, five hole‐dominated blue AIE molecules are demonstrated by adopting construction approaches of changing linkage modes and increasing intramolecular torsion together, with the aim to restrict conjugation lengths without sacrificing good EL data. Device results show that the novel synthesized materials could be applied as bifunctional materials, namely blue light‐emitting and hole‐transporting materials, with comparable EL efficiencies, and the ηC,max and ηext,max are up to 8.03 cd A−1 and 3.99% respectively, which is among the best EL performance for blue AIE luminogens.

Pd-catalyzed intramolecular aerobic oxidative C-H amination of 2-aryl-3-(arylamino)quinazolinones: synthesis of fluorescent indazolo[3,2-b]quinazolinones.

A palladium-catalyzed intramolecular aerobic oxidative C-H amination of 2-aryl-3-(arylamino)quinazolinones has been developed, providing a variety of substituted indazolo[3,2-b]quinazolinone derivatives in moderate to excellent yields. Preliminary mechanistic studies suggested that a palladacycle dimer could be the key intermediate, which underwent a cascade "rollover" cyclometalation and C-H amination sequence. Furthermore, the potential utility of these products has been demonstrated as a new class of blue fluorophores for fluorescent materials.

Highly efficient and color-stable hybrid warm white organic light-emitting diodes using a blue material with thermally activated delayed fluorescence

Hybrid white organic light-emitting diodes (WOLEDs) often undergo triplet energy loss through the triplet state of the blue fluorophors. Here, blue fluorophors with thermally activated delayed fluorescence (TADF) are introduced to solve this problem. The triplet excitons formed on blue TADF fluorophors can be harvested by either energy transfer to the low-lying triplet states of the phosphor or thermal upconversion to the emissive singlet states, eliminating the energy loss. Moreover, device structures are wisely designed to take full advantages of the charge trapping ability of the TADF dopant, 4,5-bis(carbazol-9-yl)-1,2-dicyanobenzene, achieving a color-stable warm white emission. Remarkably, a maximum forward viewing external quantum efficiency (EQE) of 22.5% and a maximum forward viewing power efficiency (PE) of 47.6 lm W−1 are achieved. These values are among the highest reported for hybrid WOLEDs and even comparable to full-phosphorescent ones, demonstrating that the strategy reported here is promising for OLED lighting.

Single white light emitting hybrid nanoarchitectures based on functionalized quantum dots

Colloidal white emitting nanostructures were successfully fabricated by covalently binding a blue emitting oligofluorene at the surface of silica beads, that incorporate orange luminescent colloidal CdSe@ZnS quantum dots (QDs). White light was achieved by carefully tuning the size of the QDs to complementarily match the emission color of the blue fluorophore and taking into account the delicate balance between the emission of the QDs in the core of the silica beads and the amount of the organic dye bound to the silica surface. The proposed approach is highly versatile as it can be extended to the fabrication of a variety of luminescent hybrid nano-objects, playing with the complementarity of the emission color of the inorganic and organic fluorophores at the nanoscale.

A multifunctional phosphine oxide–diphenylamine hybrid compound as a high performance deep-blue fluorescent emitter and green phosphorescent host

A novel phosphine oxide-diphenylamine hybrid compound POA was designed and synthesized with the aim of developing new multifunctional blue fluorophores. POA is the first kind of compound that can be used as a high-efficiency deep-blue emitter (5.4% EQE) and a host to fabricate high-performance green phosphorescent OLEDs (18.1% EQE).

Construction of efficient blue AIE emitters with triphenylamine and TPE moieties for non-doped OLEDs

In this paper, by merging the hole-dominated triphenylamine (TPA) and tetraphenylethene (TPE) moieties together with different linkage positions, four derivatives of 1,2-bis[4′-(diphenylamino)biphenyl-4-yl]-1,2-diphenylethene (2TPATPE) were successfully synthesized with confirmed structures, and their thermal, optical and electronic properties were fully investigated. Thanks to the introduction of the meta-linkage mode on the TPE core, their π-conjugation length could be effectively restricted to ensure blue emission. The non-doped OLEDs based on these four emitters exhibit blue emissions from 443–466 nm, largely blue-shifted with respect to the green emission of 2TPATPE (514 nm). Meanwhile, good electroluminescence efficiencies with Lmax, ηC,max, and ηP,max of up to 8160 cd m−2, 3.79 cd A−1, and 2.94 Im W−1 respectively, have also been obtained, further validating our rational design of blue AIE fluorophores.

Novel Blue Fluorophor with High Triplet Energy Level for High Performance Single-Emitting-Layer Fluorescence and Phosphorescence Hybrid White Organic Light-Emitting Diodes

On the basis of a D-π-A structural strategy incorporating diphenylamine as an electron-donor and 1,3,5-triazine as an electron-acceptor with a short benzene π-conjugated feature, 4-(4,6-diphenoxy-1,3,5-triazin-2-yl)-N,N-diphenylaniline (POTA), a novel blue fluorophor with high triplet energy level has been designed and synthesized to achieve high performance single-emitting-layer (single-EML) fluorescence and phosphorescence hybrid white organic light-emitting diodes (F–P hybrid WOLEDs). POTA exhibits efficient blue electrofluorescence and excellent host features for green and red phosphorescent devices. The single-EML RGB F–P hybrid WOLED based on POTA and green/red complexes shows a maximum total power efficiency of 59.8 ± 1.0 lm W–1 and a maximum total external quantum efficiency of 24.7 ± 0.7%, representing the highest efficiencies among single-EML RGB WOLEDs. Moreover, these performances are comparable with multiple-EML RGB WOLEDs even based on p-i-n structures, providing verification of the high per...

Standard fluorescent imaging of live cells is highly genotoxic

Fluorescence microscopy is commonly used for imaging live mammalian cells. Here, we describe studies aimed at revealing the potential genotoxic effects of standard fluorescence microscopy. To assess DNA damage, a high throughput platform for single cell gel electrophoresis is used (e.g., the CometChip). Light emitted by three standard filters was studied: (a) violet light [340-380 nm], used to excite DAPI and other blue fluorophores, (b) blue light [460-500 nm] commonly used to image green fluorescent protein (GFP) and Calcein AM, and (c) green light [528-553 nm], useful for imaging red fluorophores. Results show that exposure of samples to light during imaging is indeed genotoxic even when the selected wavelengths are outside the range known to induce significant damage levels. Shorter excitation wavelengths and longer irradiation times lead to higher levels of DNA damage. We have also measured DNA damage in cells expressing enhanced GFP or stained with Calcein AM, a widely used green fluorophore. Data show that Calcein AM leads to a synergistic increase in the levels of DNA damage and that even cells that are not being directly imaged sustain significant DNA damage from exposure to indirect light. The nature of light-induced DNA damage during imaging was assessed using the Fpg glycosylase, an enzyme that enables quantification of oxidative DNA damage. Oxidative damage was evident in cells exposed to violet light. Furthermore, the Fpg glycosylase revealed the presence of oxidative DNA damage in blue-light exposed cells for which DNA damage was not detected using standard analysis conditions. Taken together, the results of these studies call attention to the potential confounding effects of DNA damage induced by standard imaging conditions, and identify wavelength, exposure time, and fluorophore as parameters that can be modulated to reduce light-induced DNA damage.

Immunoreactivity for the NMDA NR1 subunit in bulbospinal catecholamine and serotonin neurons of rat ventral medulla

Bulbospinal neurons in the ventral medulla play important roles in the regulation of sympathetic outflow. Physiological evidence suggests that these neurons are activated by N-methyl-D-aspartate (NMDA) and non-NMDA subtypes of glutamate receptors. In this study, we examined bulbospinal neurons in the ventral medulla for the presence of immunoreactivity for the NMDA NR1 subunit, which is essential for NMDA receptor function. Rats received bilateral injections of cholera toxin B into the tenth thoracic spinal segment to label bulbospinal neurons. Triple immunofluorescent labeling was used to detect cholera toxin B with a blue fluorophore, NR1 with a red fluorophore, and either tyrosine hydroxylase or tryptophan hydroxylase with a green fluorophore. In the rostral ventrolateral medulla, NR1 occurred in all bulbospinal tyrosine hydroxylase-positive neurons and 96% of bulbospinal tyrosine hydroxylase-negative neurons, which were more common in sections containing the facial nucleus. In the raphe pallidus, the parapyramidal region, and the marginal layer, 98% of bulbospinal tryptophan hydroxylase-positive neurons contained NR1 immunoreactivity. NR1 was also present in all of the bulbospinal tryptophan hydroxylase-negative neurons, which comprised 20% of bulbospinal neurons in raphe pallidus and the parapyramidal region. These results show that virtually all bulbospinal tyrosine hydroxylase and non-tyrosine hydroxylase neurons in the rostral ventrolateral medulla and virtually all bulbospinal serotonin and non-serotonin neurons in raphe pallidus and the parapyramidal region express NR1, the obligatory subunit of the NMDA receptor. NMDA receptors on bulbospinal neurons in the rostral ventral medulla likely influence sympathoexcitation in normal and pathological conditions.

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.

Emission characteristics in solution-processed asymmetric white alternating current field-induced polymer electroluminescent devices

In this work, the emission characteristics of a blue fluorophor poly(9, 9-dioctylfluorene) (PFO) combined with a red emitting dye: Bis(2-methyl-dibenzo[f,h]quinoxaline)(acetylacetonate)iridium (III) [Ir(MDQ)2(acac)], are examined in two different asymmetric white alternating current field-induced polymer electroluminescent (FIPEL) device structures. The first is a top-contact device in which the triplet transfer is observed resulting in the concentration-dependence of the emission similar to the standard organic light-emitting diode (OLED) structure. The second is a bottom-contact device which, however, exhibits concentration-independence of emission. Specifically, both dye emission and polymer emission are found for the concentrations as high as 10% by weight of the dye in the emitter. We attribute this to the significant different carrier injection characteristics of the two FIPEL devices. Our results suggest a simple and easy way to realize high-quality white emission.

A novel approach towards white photoluminescence and electroluminescence by controlled protonation of a blue fluorophore

We presented a novel and simple approach towards white photoluminescence and electroluminescence based on blue emissive materials through controlled acid protonation; and this methodology has potential applicability in fabricating white OLEDs considering the simplicity of both material design and device fabrication.