Aggregation-enhanced Emission Characteristics Research Articles

Molecular engineering of blue diphenylsulfone-based emitter with aggregation-enhanced emission and thermally activated delayed fluorescence characteristics: impairing intermolecular electron-exchange interactions using steric hindrance

Thermally activated delayed fluorescence (TADF) emitters with aggregation-enhanced emission (AEE) characteristics are in high demand in organic light-emitting diodes (OLEDs) because of their strong fluorescence and high exciton utilization under electrical excitation. In this work, an AEE-active TADF emitter, 10,10′-(5-((9-phenyl-9H-carbazol-3-yl)sulfonyl)-1,3-phenylene)bis(9,9-dimethyl-9,10-dihydroacridine) (CZ-DPS-BAD), adopting diphenylsulfone skeleton as electron-accepting segment and 9-phenylcarbazole and 9,9-dimethyl-9,10-dihydroacridine as electron donors is developed. The small singlet-triplet splitting (0.13 eV) and high photoluminescence quantum yield (82 %) of CZ-DPS-BAD can attribute to the formation of large dihedral angles between electron donor-acceptors and weak electron-exchange interaction that suppress concentration quenching and exciton annihilation. The assigned characteristics result in reverse intersystem crossing rate of up to 5.0 × 105 s−1 and a delayed fluorescence lifetime of 5.3 μs. Notably, CZ-DPS-BAD behaves excellent non-doped OLED performance with the emission peak of 486 nm, the maximum current efficiency of 47.4 cd/A, the maximum power efficiency of 46.1 lm W−1, the maximum external quantum efficiency of 20.3 %, and the exciton utilizin efficiency of 83 %. It was also found that the short delayed fluorescence lifetime impair the triplet exciton annihilation resulting small efficiency roll-off in OLED. This work provides a general approach to explore new efficient and stable emitters by rationally regulating intermolecular interactions and integrating AEE and TADF, which facilitates their applications in optoelectronics.

Coumarin-substituted pyrrole derivatives with aggregation-enhanced emission characteristics for detecting the glass transition temperature of polymers

Converting natural fluorescent dyes with aggregation-caused quenching (ACQ) properties into functional fluorescent dyes with aggregation-induced emission (AIE) properties has attracted great attention in recent years. Coumarin is a kind of dye widely found in nature and has many excellent optical properties. Based on our group's research on the synthesis and properties of multiarylpyrroles (MAPs), a planar coumarin substituent was introduced into the 1-position of pyrrole to study the effect on the AIE properties of MAPs. The different numbers and positions of phenyl substituents on the pyrrole ring have a significant impact on photophysical properties. Among these compounds, MAP-1, MAP-2 and MAP-4 displayed aggregation-enhanced emission (AEE) properties, while MAP-3 showed ACQ characteristics. In addition, MAP-4 was selected as the AEE luminogen to accurately detect the glass transition temperature (Tg) of polystyrene and polymethyl methacrylate. MAP dyes provide a new method for conveniently and accurately measuring the Tg of polymers.

Violet-Blue Emitters Featuring Aggregation-Enhanced Emission Characteristics for Nondoped OLEDs with CIEy Smaller than 0.046.

High emission efficiency and finite molecular conjugation in the aggregate state are two desirable features in violet-blue emitters. Aggregation-induced emission luminogens (AIEgens) have emerged as promising luminescent materials that offer these features. Herein, we report the design and synthesis of a group of violet-blue tetraphenylbenzene-based AIEgens with photoluminescence quantum yields over 98% in their film states. When utilizing these AIEgens as nondoped emitting layers, the fabricated organic light-emitting diode exhibits a maximum external quantum efficiency of 4.34% with Commission Internationale de L'Eclairage (CIE) coordinates of (0.159, 0.035), which is amenable to the next-generation ultrahigh-definition television (UHDTV) display standard.

Thioxanthone-based organic probe with aggregation enhanced emission and exceptional mineral acids sensing abilities

The development of fluorescent probe(s) for naked eye analyte detection is an emerging area of research. Such probes can be judiciously engineered to realize analyte specific response with high sensitivity and broad applicability. Herein, we report reversible acid-base sensing ability of a donor-acceptor-donor (D-A-D) type thioxanthone-based luminophore 3,6-bis(dimethylamino)-9H-thioxanthen-9-one 10,10-dioxide (3). Photo-physical features of 3 in both the solid and solution states have also been determined. Moreover, the reported probe exhibited aggregation-enhanced emission (AEE) characteristics and pH dependent emission colour. An intramolecular charge transfer (ICT) process was observed between donor (N,N-dimethylamino) and acceptor (thioxanthone) units. The fact that changes can be seen under both the UV and visible lights without any special aid, signifies a remarkable prospect of this organic probe in distinguishing the commonly used laboratory acids of different strength.

A symmetric nonpolar blue AIEgen as nondoped fluorescent OLED emitter with low efficiency roll-off

Abstract Blue emitters are necessary for achieving full-color displaying OLEDs, however, most blue emitters show low efficiency, short lifetime or serious efficiency roll-off, hindering the development of OLED techniques. In this research, a nonpolar symmetric aggregation-induced emission (AIE) emitter was designed and constructed through facile steps, with the triphenylamine-end, anthracene-spacer and tetraphenylethene (TPE)-center. This emitter exhibited good thermal stability and aggregation-enhanced emission (AEE) characteristics, based on which non-doped blue OLED device was readily fabricated with the maximum external quantum efficiency (EQE) of 2.7% and also with no efficiency roll-off even at 1000 cd m−2, indicative of high efficiency and good stability as fluorescent emitter.

Polymorphic Pure Organic Luminogens with Through-Space Conjugation and Persistent Room-Temperature Phosphorescence.

Pure organic luminogens with persistent room-temperature phosphorescence (p-RTP) have attracted increasing attention owing to their vital significance and potential applications in security inks, bioimaging, and photodynamic therapy. Previously reported p-RTP luminogens normally possessed through-bond conjugation. In this work, we report a pure organic luminogen, AN-MA, the Diels-Alder cycloaddition adduct of anthracene (AN) and maleic anhydride (MA), which possesses isolated phenyl groups and an anhydride moiety. AN-MA exhibits aggregation-enhanced emission (AEE) characteristics with efficiency of approximately 2 % and up to 8.5 % in solution and crystals, respectively. Two polymorphs of AN-MA were readily obtained that were able to generate UV emission from individual phenyl rings together with bright blue emission owing to the effective through-space conjugation. Moreover, p-RTP with a lifetime of up to approximately 1.6 s was obtained in the crystals. These results not only reveal a new system with both fluorescence and RTP dual emission but also suggest an alternative through-space conjugation strategy towards pure organic p-RTP luminogens with tunable emissions.

1,1′-Bi(2-naphthol-4,5-dicarboximide)s: blue emissive axially chiral scaffolds with aggregation-enhanced emission properties

Novel electron-deficient 1,1′-binaphthol derivatives bearing two dicarboximide groups at the peri-positions show intense blue luminescence and aggregation-enhanced emission characteristics.

Twisted intramolecular charge transfer and aggregation-enhanced emission characteristics based quinoxaline luminogen: photophysical properties and a turn-on fluorescent probe for glutathione

A light-up fluorescent probe (QUPY-S) for glutathione detection based on a triphenylethylene-containing quinoxaline pyridinium salt has been developed.

Frontispiece: Aggregation‐Induced Emission of Multiphenyl‐Substituted 1,3‐Butadiene Derivatives: Synthesis, Properties and Application

Multiphenyl-substituted 1,3-butadiene (MPB), as a core structure that includes tetraphenyl-1,3-butadiene, hexaphenyl-1,3-butadiene and their derivatives, shows typical aggregation-induced emission or aggregation-enhanced emission (AIE/AEE) characteristics. In their Minireview on page 15965 ff., J. Shi, Y. Dong et al. summarize the structural design, excellent properties and potential applications of all these MPBs that have a variety of conformations, such as EE, EZ, and ZZ, and present different fluorescence responses under external stimuli. Therefore, as new members of AIE/AEE families, MPBs will become “star” structures suitable for the fast-developing AIE/AEE fields and shine on AIE/AEE-related researches.

Aggregation-Induced Emission of Multiphenyl-Substituted 1,3-Butadiene Derivatives: Synthesis, Properties and Application.

Organic functional materials, including conjugated molecules and fluorescent dyes, have been intensely developed in recent years because they can be applied in many fields, such as solar cells, biosensing and bioimaging, and medical adjuvant therapy. Organic functional materials with aggregation-induced emission or aggregation-enhanced emission (AIE/AEE) characteristics have increasingly attracted attention due to their high quantum efficiency in the aggregated or solid state. A large variety of AIE/AEE materials have been designed and applied during the exponential growth of research interest in the abovementioned fields. Multiphenyl-substituted 1,3-butadiene (MPB), as a core structure that includes tetraphenyl-1,3-butadiene, hexaphenyl-1,3-butadiene and their derivatives, show a typical AIE/AEE feature and can be potentially used in all the above-mentioned fields. This review summarizes the design principles, the corresponding syntheses, and the structure-property relationships of MPBs, as well as their excellent innovative functionalities and applications. This review will be useful for scientists conducting chemistry, materials, and biomedical research in AIE/AEE-related fields.

Application of a Novel "Turn-on" Fluorescent Material to the Detection of Aluminum Ion in Blood Serum.

A novel "turn-on" fluorescent bioprobe, 1,2,3,4,5-penta(4-carboxyphenyl)pyrrole sodium salt (PPPNa), with aggregation-enhanced emission characteristics was synthesized for the in situ quantitative detection of Al3+ in serum. It exhibited a high selectivity to Al3+ in both simulated serum and fetal calf serum with no interferences from other metal ions or serum components observed and no isolation required. A weak interaction between PPPNa and serum albumin was found, which caused no interference, but enhanced fluorescence response of PPPNa to Al3+ and improved detection sensitivity. The limit of detection was determined to be 1.50 μmol/L Al3+ in phosphate-buffered saline solution containing 33 μg/mL bovine serum albumin (BSA) and decreased to 0.98 μmol/L as BSA concentration increased to 100 μg/mL. The fluorescence "turn-on" mechanism of the PPPNa probe to detect Al3+ was proposed. A bidentate complex is formed between the carboxy group of PPPNa and Al3+, causing the photoluminescence (PL) emission enhancement by aggregation. BSA chains further strengthen the stacking compactness of the aggregates of PPPNa and Al3+ and consequently enhance the PL emission of PPPNa by further promoting the restriction of intramolecular rotation of the phenyl ring. Its application to the in situ Al3+ was successfully demonstrated with HeLa cells and NIH 3T3 cells. The low cytotoxicity and highly selective response of PPPNa to Al3+ endow its great potentials to in vivo detecting and imaging of Al3+ as well as an absorbent of Al3+.

Triphenylacrylonitrile decorated N-phenylcarbazole: Isomeric effect on photophysical properties

Efficient solid-state emitters show promising applications in optical, biological and optoelectronic areas. Understanding the structure-property relationships is essential to explore their applications. In this contribution, several isomers of triphenylacrylonitrile (TPAN) decorated N-phenylcarbazole (PCZ) were synthesized and their photophysical properties were investigated. The substitution position exerts a distinct influence on the photophysical properties, including absorption, emission and mechanochromism. All luminogens demonstrate aggregation-enhanced emission (AEE) characteristics with efficiency up to 56.80%. Except o-TPANPCZ, other isomers show distinct reversible luminescent mechanochromism, owing to the destruction and restoration of their twisted conformations and intermolecular interactions in the crystalline and amorphous states.

Facile Polymerization of Water and Triple-Bond Based Monomers toward Functional Polyamides

Water is an abundant, natural, and sustainable resource. However, it has not been used as a monomer for the construction of polymers. In this paper, we take this challenge and develop a new polymerization of water and triple-bond based monomers of isocyanides and bromoalkynes, and polyamides with high molecular weights (up to 41 700) and stereoregularities (the fraction of Z-isomer generally higher than 80%) are obtained in excellent yields (up to 98.1%) under mild reaction conditions. The polymers possess good solubility and exhibit high thermal stability and refractive index. The tetraphenylethene-containing polymers show the unique aggregation-enhanced emission (AEE) characteristics. Moreover, thanks to their containing bromoacrylamide groups in the main chains, these polyamides could be easily postmodified through different reactions, providing a convenient platform for polymer functionalization. Thus, this work not only established a stereoselective polymerization of water and triple-bond based monom...

Tetraphenylpyrimidine-Based AIEgens: Facile Preparation, Theoretical Investigation and Practical Application.

Aggregation-induced emission (AIE) has become a hot research area and tremendous amounts of AIE-active luminogens (AIEgens) have been generated. To further promote the development of AIE, new AIEgens are highly desirable. Herein, new AIEgens based on tetraphenylpyrimidine (TPPM) are rationally designed according to the AIE mechanism of restriction of intramolecular motion, and facilely prepared under mild reaction conditions. The photophysical property of the generated TPPM, TPPM-4M and TPPM-4P are systematically investigated and the results show that they feature the aggregation-enhanced emission (AEE) characteristics. Theoretical study shows the high-frequency bending vibrations in the central pyrimidine ring of TPPM derivatives dominate the nonradiative decay channels. Thanks to the AEE feature, their aggregates can be used to detect explosives with super-amplification quenching effects, and the sensing ability is higher than typical AIE-active tetraphenylethene. It is anticipated that TPPM derivatives could serve as a new type of widely used AIEgen based on their facile preparation and good thermo-, photo- and chemostabilities.

Solution‐Processable Thermally Activated Delayed Fluorescence White OLEDs Based on Dual‐Emission Polymers with Tunable Emission Colors and Aggregation‐Enhanced Emission Properties

AbstractThermally activated delayed fluorescence (TADF) white organic light‐emitting diodes (WOLEDs) have drawn tremendous interest and have been extensively studied because of harvesting both triplet and singlet excitons without heavy metals. However, single white‐light‐emitting polymers are currently limited and few strategies exist to design these materials. Herein, a new strategy is proposed to develop the polymers with tunable emission colors by combining fluorescence and TADF based on aggregation‐enhanced emission (AEE) characteristics. The polymers containing different ratios of pendant 2‐(10H‐phenothiazin‐10‐yl)dibenzothiophene‐S,S‐dioxide units with yellow TADF emission and dibenzothiophene units with blue fluorophor emission, which display both TADF and AEE characteristics, are synthesized successfully. Among them, the emission color of P3 in different tetrahydrofuran/water mixtures changes from greenish‐blue to white or yellow. Moreover, P3 displays white emission in the solid state dispersing by poly(methyl methacrylate). In addition, electroluminescent device of P3 achieve white light emission with high color rending indexes (CRI) and low turn‐on voltages (V on ). P3 OLEDs show two‐color warm‐white emission with high CRI of 77, low V on of 2.9 V, CEmax of 23.0 cd A−1, PEmax of 32.8 lm W−1, external quantum efficiency (EQE)max of 10.4% with Commission Internationale de l'Eclairage coordinates of (0.37, 0.38) at 5 V. Moreover, EQE of 2.6%, CE of 5.7 cd/A, PE of 4.7 lm W−1 at 100 cd m−2 are obtained. To the best of our knowledge, this work reports the first example of warm‐white TADF polymer OLEDs.

A facile synthesis of novel near-infrared pyrrolopyrrole aza-BODIPY luminogens with aggregation-enhanced emission characteristics.

Here we report the facile synthesis of two triphenylethylene-modified pyrrolopyrrole aza-BODIPY dyes with an aggregation-enhanced emission feature. NIR-emitting nanoparticles with remarkable photostability properties and applications in bioimaging were generated due to their good dispersity in water and biocompatibility.

Polyurethanes with aggregation-enhanced emission characteristics: preparation and properties.

An amino-terminated poly(propylene glycol)-modified tetraaryl-buta-1,3-diene derivative (TABDAA) was introduced to synthesize polyurethanes with different ratios of soft/hard segments. A mixture of TABDAA and poly(tetrahydrofuran) 1000 as the soft segments was reacted with 4,4-diphenylmethane diisocyanate and 1,4-butanediol as the hard segments in molar ratios of 1 : 2 : 1, 2 : 3 : 1, and 3 : 4 : 1 to give the desired polyurethanes named TMPU-211, TMPU-321 and TMPU-431, respectively. The three polyurethanes exhibited different aggregation-enhanced emission (AEE) behaviors because of their different soft/hard segment ratios. The polyurethanes with a higher soft segment content tended to form bigger particles in a DMF/water mixture solution, thus causing a sharper increase in their fluorescence intensity. In addition, the polyurethane films exhibited different fluorescence intensities after different heat treatments. After a quenching treatment of the soft segments in the polyurethane films, the fluorescence intensity dropped greatly. When these quenched polyurethane films were thermally annealed at 60 °C for 24 hours, their fluorescence intensity exceeded the initial intensity of the as-prepared films. Differential scanning calorimetry results showed that the polyurethane films in the quenched condition did not present the endothermal melting peak of the soft segments, and the melting peaks appeared again after thermal annealing. AFM experiments showed that an ordered arrangement was achieved after the heat treatment of these AEE polyurethane films. These results demonstrated that the polymer structure had a significant effect on the AEE properties of the polyurethane films, and more importantly, it is of great significance in improving the fluorescence emission of the AEE polymers and also for their potential application in fluorescent probes, stimuli-responsive materials, PLED devices and so on.

Aggregation-enhanced emission active tetraphenylbenzene-cored efficient blue light emitter.

A tetraphenylbenzene (TPB) cored luminophore of TPB-AC with aggregation-enhanced emission characteristics was designed and synthesized. TPB-AC could be potentially applied for the fabrication of high performance organic light-emitting diodes (OLEDs) with blue light emission.

Reversible multicolor switching via simple reactions of the AIE-characteristic molecules

A multicolor switching was achieved via simple reversible coordinationand acetalation reaction between aldehydes, tri(pentafluorophenyl)borane (BCF) and methanol. The coordination [HPB → BCF] of 4,4′-[(1E,3E)-1,2,3,4-tetraphenylbuta-1,3-diene-1,4-diyl]- dibenzaldehyde (E,E-HPB) to tri(pentafluorophenyl)borane can change the emissive wavelength from 550 to 630 nm, while transformation of the aldehyde into acetal can change the emissive wavelength from 550 to 530 nm in the presence of methanol. More important, these reactions can access reversibility easily and tune the emission color repeatedly between cyan, yellow and red. All of these dyes show typical aggregation-induced emission (AIE) or aggregation-enhanced emission (AEE) characteristics. In addition, a tunable photoluminescence mechanism is proposed based on the characterization data including NMR, XRD, MS and IR. The result may provide a new design strategy for the multicolor switches and their related applications.

Red fluorescent siloles with aggregation-enhanced emission characteristics

A series of new red fluorescent siloles consisting of a silole core and dimesitylboranyl substituent connected with a furan, thiophene, and selenophene bridges were synthesized and characterized. The optical properties, electronic structures, and electroluminescence (EL) performances were investigated. The emission wavelengths were red-shifted from the siloles with furan, to those with thiophene, and then selenophene. The thiophene, and selenophene-containing siloles, (MesB)2DTTPS, and (MesB)2DSTPS, showed the typical aggregation-enhanced emission (AEE) feature, while furan-containing one, (MesB)2DFTPS, showed slight emission decrease as the aggregate formation. Theoretical calculations were carried out to explain the difference in the optical properties. Undoped OLEDs using these red siloles as light-emitting layers were fabricated. The device of (MesB)2DTTPS exhibited the best performance. It radiated red EL emission at 589 nm, and afforded good maximum luminance, current, power, and external quantum efficiency of 13300 cd n−2, 4.3 cd A−1, 2.9 lm W−1, and 1.8%, respectively.