Emission Enhancement Characteristics Research Articles

Fluorescent aggregates of AIEE active triphenylene derivatives for the sensitive detection of picric acid

Fluorescent aggregates of triphenylene derivatives 3 and 5 having aggregation induced emission enhancement (AIEE) characteristics have been developed which selectively detect picric acid.

A novel fluorene-based aggregation-induced emission (AIE)-active gold(i) complex with crystallization-induced emission enhancement (CIEE) and reversible mechanochromism characteristics.

A new fluorene-based AIE-active gold(i) complex was designed and synthesized. The novel luminogen exhibits a crystallization-induced emission enhancement (CIEE) effect and reversible mechanochromic behavior with fluorescence changes between green and yellow emissions.

The aggregation-induced emission enhancement properties of BF2 complex isatin-phenylhydrazone: Synthesis and fluorescence characteristics

Isatin-phenylhydrazone derivatives and their corresponding BF2 complexes were efficiently synthesised by a three-step reaction starting from isatin and phenylhydrazine hydrochloride. The fluorescence properties of the isatin-phenylhydrazone derivatives and derived BF2 complexes were investigated in different organic solvents, in the solid state and in mixed solvent solutions of THF and H2O. These fluorescent dyes exhibited low fluorescent intensity in solution but a high fluorescent intensity as aggregates and in their solid state due to the interesting aggregation-induced emission enhancement characteristics which were caused by the inhibition of intramolecular rotation in the single molecule state. Information supporting this inference was supported by single crystal X-ray analysis.

Synthesis of unsymmetric bipyridine-Pt(II) -alkynyl complexes through post-click reaction with emission enhancement characteristics and their applications as phosphorescent organic light-emitting diodes.

Two unsymmetric bipyridine-platinum(II)-alkynyl complexes have been synthesised by a post-click reaction. These metal complexes are found to exhibit emission enhancement properties. The photoluminescence quantum yield can be significantly increased from 0.03 in solution to 0.72 in solid-state thin films. Efficient solution-processable organic light-emitting diodes have been fabricated by utilizing these complexes as phosphorescent dopants. A high external quantum efficiency of up to 5.8% has been achieved.

Trace analysis of uranyl ion (UO22+) in aqueous solution by fluorescence turn-on detection via aggregation induced emission enhancement effect

A sensitive fluorescence turn-on method for trace amounts of uranyl ion (UO22+) in solution has been developed in this study, based on aggregation induced emission enhancement (AIEE) characteristics of 4-pethoxycarboxyl salicylaldehyde azine (PCSA) induced by complex interaction between UO22+ and PCSA. Under optimized conditions, a fluorescence enhancement at 540nm could be observed, which was linearly related to the concentration of UO22+ in the range of 1–25ppb (part per billion). Analytical data showed that a detection limit of 0.2ppb was achieved with the relative standard deviation (R.S.D.) 1.3% (n=5). The proposed method was successfully utilized in quantifying UO22+ in fuel processing wastewaters.

Fluorene-based novel highly emissive fluorescent molecules with aggregate fluorescence change or aggregation-induced emission enhancement characteristics

A series of luminogens containing formamide or fluorenone units, based on fluorene, have been synthesized and characterized by NMR spectroscopy, mass spectrometry and elemental analysis. Their aggregate fluorescence change and aggregation-induced emission enhancement (AIEE) characteristics were investigated by luminescence and UV/Vis spectroscopies. The results indicate that luminogens 1d and 2d, containing formamide units, exhibit significant fluorescence color changing upon aggregate formation, which is a newly observed uncommon and interesting aggregation-induced emission phenomenon. Although the luminogen 3d, with one fluorenone unit and one fluorene unit, was weakly emissive in solution, it was highly fluorescent in the aggregated state and demonstrates typical AIEE characteristics. In comparison with 3d, the luminogen 4d with one fluorenone unit and two fluorene units showed weaker AIEE behavior. In thin-films and in the solid state, luminogen 1d shows intense yellow-green emission, and other luminogens show strong yellow emitting. Among these luminogens, 4d exhibits the highest solid-state emission quantum yield.

Schiff base modified α-cyanostilbene derivative with aggregation-induced emission enhancement characteristics for Hg2+ detection

A Schiff base functionalized α-cyanostilbene derivative (TS) has been synthesized via a simple and straightforward method and characterized by FT-IR, 1H NMR, 13C NMR and mass spectra. TS possessed excellent AIEE properties and exhibited “turn-on” fluorescent responses to Hg2+. The results of UV–vis and fluorescence titration experiments revealed that TS was selective and sensitive to Hg2+ in pure THF and aqueous environment. The coordination of TS and Hg2+ ions generated TS–Hg complex locked the “dancing molecule” because of the flexible chain in the middle of the molecule and the complex was lower soluble induced formation of large aggregates that further limited the non-radiative relaxation channel enhanced emission after adding Hg2+ ions in aqueous solution, which had been confirmed by 1H NMR and dynamic light scattering (DLS).

Multistimuli-responsive azobenzene nanofibers with aggregation-induced emission enhancement characteristics.

A new azobenzene-based chromophore was synthesized to create one-dimensional (1D) nanofibers with aggregation-induced emission enhancement characteristics. The enhanced red fluorescence of the fibrous structures can be switched off via mechanical pressure, friction, or heat by pressing, rubbing, or annealing.

Synthesis and self-assembly of carbazole-based amphiphilic triblock copolymers with aggregation-induced emission enhancement

Well-defined amphiphilic triblock copolymers with carbazole pendants (PVACB-PEG2000-PVACB) were synthesized via the combination of reversible addition–fragmentation chain transfer (RAFT) polymerization and “click” chemistry. All of the intermediate and final products were characterized using 1H NMR, FT-IR and GPC. Cup-shaped vesicles were then fabricated via self-assembly of the carbazole-containing amphiphilic triblock copolymers in aqueous solution, which were characterized by TEM and SEM. These novel carbazole-based polymeric vesicles were found to exhibit interesting aggregation-induced emission enhancement (AIEE) characteristics compared with the fluorescence intensity of the polymers in organic solution.

Aggregation-Induced Emission Enhancement in Alkoxy-Bridged Binuclear Rhenium(I) Complexes: Application as Sensor for Explosives and Interaction with Microheterogeneous Media

The aggregation-induced emission enhancement (AIEE) characteristics of the two alkoxy-bridged binuclear Re(I) complexes [{Re(CO)3(1,4-NVP)}2(μ2-OR)2] (1, R = C4H9; 2, C10H21) bearing a long alkyl chain with 4-(1-naphthylvinyl)pyridine (1,4-NVP) ligand are illustrated. These complexes in CH2Cl2 (good solvent) are weakly luminescent, but their intensity increased enormously by almost 500 times by the addition of poor solvent (CH3CN) due to aggregation. By tracking this process via UV-vis absorption and emission spectral and TEM techniques, the enhanced emission is attributed to the formation of nanoaggregates. The nanoaggregate of complex 2 is used as a sensor for nitroaromatic compounds. Furthermore, the study of the photophysical properties of these binuclear Re(I) complexes in cationic, cetyltrimethylammonium bromide (CTAB), anionic, sodium dodecyl sulfate (SDS), and nonionic, p-tert-octylphenoxypolyoxyethanol (TritonX-100, TX-100), micelles as well as in CTAB-hexane-water and AOT-isooctane-water reverse micelles using steady-state and time-resolved spectroscopy and TEM analysis reveals that the nanoaggregates became small and compact size.

Large cyano- and triazine-substituted D–π–A–π–D structures as efficient AIEE solid emitters with large two-photon absorption cross sections

A series of new large π-conjugated molecules including diphenylamine and carbazole have been synthesized and characterized (3a–c). All compounds display aggregation-induced emission enhancement (AIEE) characteristics: exhibiting weak fluorescence in pure THF, while a significant AIEE effect is observed in mixtures with a water fraction (fw) of 90% with a sharp increase in fluorescence intensity. Combining intramolecular charge transfer (ICT) characteristics and AIEE features, 3a–c are intense solid emitters (589 nm, 546 nm and 556 nm, respectively) with high quantum efficiencies of 18.1%, 27.4% and 14.9%, respectively. Their two-photon absorption (2PA) properties have been investigated using the open-aperture Z-scan technique, and the values of the 2PA cross section at 800 nm for 3a–c are 1363 GM, 413 GM and 5782 GM, respectively. Their excellent 2PA properties and solid quantum efficiencies pave the way for their potential use in biophotonic and optoelectronic applications.

Synthesis, crystal Structures and aggregation-induced emission enhancement of aryl-substituted cyclopentadiene derivatives

A series of cyclopentadiene derivates, namely, 1,2,4-triphenylcyclopenta-1,3-diene (1), 1,2-diphenyl-4-(p-methoxyphenyl)cyclopenta-1,3-diene (2) and 1,2-di(p-methoxyphenyl)-4-phenylcyclopenta-1,3-diene (3), were synthesized and their photoluminescence properties in solutions and aggregation state were investigated. Different photoluminescence properties of 1–3 were tuned by changing types and replace position of substituent groups. These cyclopentadiene derivates display solvent-dependent fluorescence emissions and typical aggregation-induced emission enhancement (AIEE) characteristics. The crystal structure analysis reveals that intermolecular C–H…π interactions and X-aggregation molecule stacking have a dramatic effect on the photoluminescent properties of 1–3. Additionally, the DFT calculations of these compounds were investigated.

Aggregation-induced emission enhancement based on 11,11,12,12,-tetracyano-9,10-anthraquinodimethane

By introducing phenyl groups into the 2- and 6-positions of 11,11,12,12-tetracyano-9,10-anthraquinodimethane, a material (dP-TCAQ) with aggregation-induced emission enhancement (AEE) characteristics was synthesized. The AEE phenomenon was explained by analysis of its solid-state packing mode. To our best knowledge, this is the first report regarding 11,11,12,12-tetracyano-9,10-anthraquinodimethane with AEE behaviour.

The AIEE effect and two-photon absorption (TPA) enhancement induced by polymerization: synthesis of a monomer with ICT and AIE effects and its homopolymer by ATRP and a study of their photophysical properties

A monomer including pyrazoline and l,8-naphthalimide moieties and its homopolymer were prepared by atom transfer radical polymerization (ATRP). The emission of the monomer can be tuned by choosing solvents with different polarities or aggregation-induced emission (AIE). The rotation of the fluorophore of the homopolymer was further limited by both the side chain and the flexible main chain, resulting in emission enhancement in strong polar solution and aggregation-induced emission enhancement (AIEE) characteristics. More interestingly, compared to that of the monomer, the two-photon absorption (TPA) property of the homopolymer is much more enhanced both in toluene and aggregates. This is attributed to the amplification effect of the polymer chain. This may become a new and promising method with which to prepare TPA polymers.

A pentacenequinone derivative with aggregation-induced emission enhancement characteristics for the picogram detection of Fe3+ ions in mixed aqueous media

The binding behavior of nanoaggregates of pentacenequinone derivative 1 having thiophene groups has been investigated toward various cations (Fe(3+), Fe(2+), Pd(2+), Mg(2+), Cd(2+), Hg(2+), Ni(2+), Zn(2+), Cu(2+), Pb(2+), Co(2+), K(+), Na(+) and Li(+)) using UV-vis and fluorescence spectroscopy. Among the various cations tested, nanoaggregates of compound 1 show a selective and sensitive response towards ferric ions. Further, the paper strips coated with a solution of nanoaggregates of 1 can detect ferric ions at the picogram level, thus providing a simple, portable and low cost method for the detection of ferric ions at the picogram level in aqueous solution.

A highly selective 1,8-naphthalimide probe for recognition of casein based on aggregation induced emission enhancement characteristics

A water-soluble 1,8-naphthalimide-based fluorescent probe 1, bearing four acetic carboxylic groups, exhibited high selectivity and sensitivity for recognition of casein based on the aggregation induced emission enhancement (AIEE) character. The AIEE mechanism of probe 1 with casein was studied by fluorescence and circular dichroism (CD) spectra. Base on the AIEE characteristics of probe 1, a novel fluorometric method for casein quantification in the PBS (pH = 7.4) was developed. The linear range of the calibration curve was 0.1–11.0 μg mL−1 with a correlation coefficient of 0.9978. The detection limit was estimated to be 2.0 ng mL−1. The proposed method has been applied to the determination of casein in milk powder samples and the results were in good agreement with the result of Biuret method.

A New Series of C‐6 Unsubstituted Tetrahydropyrimidines: Convenient One‐Pot Chemoselective Synthesis, Aggregation‐Induced and Size‐Independent Emission Characteristics

A new series of C-6 unsubstituted tetrahydropyrimidines 6 have been directly synthesized via a convenient urea-catalyzed chemoselective five-component reaction (5CR) under mild conditions. Compounds 6 show typical aggregation-induced emission enhancement (AIEE) characteristics because they are practically no emissive in solution but emit blue or green fluorescence in aggregates with fluorescence yield up to 93%. One of the 5CR products, 6aa, exhibits blue- and green-fluorescence aggregates (bf- and gf-aggregates). The bf- and gf-aggregates are prepared under different conditions and proved to result from different J-aggregations by single-crystal X-ray analysis. In addition, the bf- and gf-aggregates of 6aa show unusual size-independent emission (SIE) characteristics because their maximum emission wavelengths in different sizes (suspension particles, film, powder and crystals) are the same, 434 and 484 nm, respectively. Based on the obtained experimental results, the 5CR mechanism, the origins of AIEE and SIE characteristics are discussed.

P-Carboxyl- N-salicylideneanilines: Simple but efficient chromophores for one-dimensional microrods with aggregation-induced emission enhancement (AIEE) characteristics

In this study, p-carboxyl- N-salicylideneaniline ( pCSA) derivatives were simply synthesized by condensing salicylaldehyde and primary amine. With two planar π-conjugated moieties linked by rotatable C–N single bond in the molecular structure, pCSA derivatives were characteristic of aggregation-induced emission enhancement (AIEE) properties, exhibiting strong fluorescence in solid state. Facilely recrystallized from organic solvent, one-dimensional (1D) microrods of pCSA were prepared with green, yellow and orange AIEE colors depending on substituents on salicylaldimine moiety. The obtained 1D microrods could be utilized as potential optical waveguides for propagating and manipulating light in miniaturized devices.

A ratiometric fluorescent pH probe based on aggregation-induced emission enhancement and its application in live-cell imaging

A ratiometric fluorescent pH probe, 4-carboxylaniline-5-chlorosalicylaldehyde Schiff base (1) was synthesized via a facile reaction and used for pH sensing in live cells. While exhibiting weak fluorescence when dispersed in solution, 1 displayed aggregation-induced emission enhancement (AIEE) characteristics in its aggregate/solid state, as a result of the restriction of free intramolecular rotation of a C–N bond and the non-planar configuration in the aggregate/solid state. The integration of hydroxyl and carboxyl groups provided 1 with a ratiometric fluorescent response to pH based on AIEE and the pH-dependent spectral characteristics of compound 1, with proton dissociation constants pKa1 and pKa2 of 4.8 ± 0.1 and 7.4 ± 0.1, respectively. The probe exhibited a significant fluorescence color change from orange to green with an intensity ratio (I516 nm/ I559 nm) enhanced when the pH increased from 5.0 to 7.0 in aqueous solution. Confocal fluorescence imaging of intracellular pH through ratiometric response was successfully achieved in live HepG2 cells. The results demonstrate that probe 1 is a good candidate for monitoring pH fluctuations in live cells with good selectivity, stability, and excellent membrane permeability.

Aggregation-induced emission enhancement characteristics of naphthalimide derivatives and their applications in cell imaging

Novel naphthalimide derivatives (NIM) with donor–acceptor architecture were successfully constructed and their unique fluorescent properties were investigated. In particular, the fluorescence intensities of 4-methoxystyrene substituted NIM-1 were solvent independent and its quantum yields varied from 0.4 in toluene to 0.52 in MeOH. However, 4-(N,N-diphenylamino) styrene substituted NIM-2 and 4-nitrostyrene substituted NIM-3 exhibited low luminescence in dilute solutions but were efficiently fluorescent under conditions of molecular aggregation. NIM-2 showed strong solid fluorescence with a longer wavelength emission and larger Stokes shift. In addition, NIM-3 showed unexpected blue-green fluorescence due to the formation of fluorescent organic nanoparticles (FONs) under mixed solution. These two cases were ascribed to the aggregation-induced enhanced emission (AIEE) effects and which can also reasonably explain the bright cellular images observed when cells were incubated with NIM-2 and NIM-3. Furthermore, compound NIM-2 can be used to recognize cancer cells owing to its subcellular behaviour.