Aggregation-induced Emission Enhancement Characteristics Research Articles

Aggregation induced emissive carbazole-based push pull NLOphores: Synthesis, photophysical properties and DFT studies

2-Alkoxy-9-methyl-9H-carbazole-3-carbaldehyde based push pull chromophore were efficiently synthesized by a multi-step reaction starting from 9H-carbazole-2-ol. The fluorescence properties of these D–π–A chromophores were investigated in various solvents of varying polarities and in mixed solvent solutions of DMF and H2O. They exhibited low fluorescent intensity in solution but a high fluorescent intensity in aggregate forms and in their solid state due to the promising aggregation-induced emission enhancement characteristics. These dyes were fully characterized by FT-IR, 1H NMR and HRMS spectra. The ratio of ground to excited state dipole moment of the novel push pull chromophore were calculated by Bakhshiev and Bilot–Kawski correlations. All the four dyes show more or less twisted intramolecular charge transfer (TICT) characteristics. They show a large first hyperpolarizability value ranging from 189–721 × 10−30 esu by theoretical method and 73–330 × 10−30 esu by experimental method.

Unimolecular Photopolymerization of High-Emissive Materials on Cylindrical Self-Assemblies

We report a novel self-assembly pathway from a bis(imidazolyl) diphenyl–diacetylene (DPDA) compound as a realization of self-templated photopolymerization with high polymerization degrees. The work takes advantage of a cylindrical self-assembly that strengthens the preorganization of the diphenyl–diacetylene moiety at the single molecular level. On this basis, photopolymerization of DPDA can be conducted smoothly to form high-molecular-weight polydiphenyl diacetylene. Such a cylindrical self-assembly is highly dependent on molecular structure, and control studies show that only oligomers can be formed on random self-assemblies from a monoimidazolyl or nonimidazolyl diphenyl–diacetylene compound. Moreover, the cylindrical self-assembly based systems bear aggregation-induced emission enhancement characteristics and are solution processable. The leading thin-film could afford a selectively tunable function in luminescent micropatterns.

Facile Decoration of Multiwalled Carbon Nanotubes with Hetero-oligophenylene Stabilized-Gold Nanoparticles: Visible Light Photocatalytic Degradation of Rhodamine B Dye.

A hetero-oligophenylene derivative 3 has been designed and synthesized which forms fluorescent spherical aggregates in mixed aqueous media due to its aggregation-induced emission enhancement characteristics. These fluorescent aggregates act as a ratiometric probe for the detection of gold ions in aqueous media and serve as reactors and stabilizers for the preparation of gold nanoparticles. The in situ generated gold nanoparticles have been decorated on multiwalled carbon nanotubes to form AuNPs@MWCNTs nanohybrid materials, which serve as recyclable photocatalysts for carrying out degradation of rhodamine dye in aqueous media.

Characterization of the Aggregation-Induced Enhanced Emission of N,N'-bis(4-methoxysalicylide)benzene-1,4-diamine.

N,N'-bis(4-methoxysalicylide)benzene-1,4-diamine (S1) was synthesized from 4-methoxysalicylaldehyde and p-phenylenediamine and it was found to exhibit interesting aggregation-induced emission enhancement (AIEE) characteristics. In aprotic solvent, S1 displayed very weak fluorescence, whilst strong emission was observed when in protic solvent. The morphology characteristics and luminescent properties of S1 were determined from the fluorescence and UV absorption spectra, SEM, fluorescence microscope and grading analysis. Analysis of the single crystal diffraction data infers that the intramolecular hydrogen bonding constitutes to a coplanar structure and orderly packing in aggregated state, which in turn hinders intramolecular C-N single bond rotation. Given that the three benzene rings formed a large plane conjugated structure, the fluorescence emission was significantly enhanced. The absolute fluorescence quantum yield and fluorescence lifetime also showed that radiation transition was effectively enhanced in the aggregated state. Moreover, the AIEE behavior of S1 suggests there is a potential application in the fluorescence sensing of some volatile organic solvents.

Synthesis of Buta-1,3-dienes through Palladium-Catalyzed Homocoupling of Aromatic Alkenes

A series of buta-1,3-dienes have been directly synthesized via a convenient palladium-catalyzed homodehydrogenation coupling reaction of aromatic alkenes under mild conditions. The homocoupling reaction enables a rapid synthesis of multisubstituted butadiene which shows typical aggregation-induced emission enhancement (AIEE) characteristics because it is practically not emissive in solution but emits blue fluorescence in aggregates.

Difunctional chemosensor for Cu(ii) and Zn(ii) based on Schiff base modified anthryl derivative with aggregation-induced emission enhancement and piezochromic characteristics

Three new anthryl Schiff base derivatives containing a similar molecular structure were synthesized through a simple method and their fluorescent properties were investigated in detail.

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.

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.

Insights into the AIEE of 1,8-naphthalimides (NPIs): inverse effects of intermolecular interactions in solution and aggregates.

Systematic structural perturbation has been used to fine-tune and understand the luminescence properties of three new 1,8-naphthalimides (NPIs) in solution and aggregates. The NPIs show blue emission in the solution state and their fluorescence quantum yields are dependent upon their molecular rigidity. In concentrated solutions of the NPIs, intermolecular interactions were found to quench the fluorescence due to the formation of excimers. In contrast, upon aggregation (in THF/H2O mixtures), the NPIs show aggregation-induced emission enhancement (AIEE). The NPIs also show moderately high solid-state emission quantum yields (ca. 10-12.7 %). The AIEE behaviour of the NPIs depends on their molecular rigidity and the nature of their intermolecular interactions. The NPIs 1-3 show different extents of intermolecular (π-π and C-H⋅⋅⋅O) interactions in their solid-state crystal structures depending on their substituents. Detailed photophysical, computational and structural investigations suggest that an optimal balance of structural flexibility and intermolecular communication is necessary for achieving AIEE characteristics in these NPIs.

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.

Halogenated salicylaldehyde azines: The heavy atom effect on aggregation-induced emission enhancement properties

This study investigates the heavy-atom effect (HAE) on aggregation-induced emission enhancement (AIEE) properties of salicylaldehyde azines. For this purpose, a series of halogenated salicylaldehyde azine derivatives, namely, chloro-salicylaldehyde azine (1), bromo-salicylaldehyde azine (2) and iodo-salicylaldehyde azine (3) are synthesized. 1 and 2 display typical AIEE characteristics of salicylaldehyde azine compounds; whereas for the iodo-substituent in 3, is found to be effective “external” heavy atom quenchers to salicylaldehyde azine fluorescence in aggregated state. Based on its weak fluorescence in aggregated state and relative strong fluorescence in dispersed state, 3 can also be applied as a turn-on fluorescence probe for egg albumin detection attributed to hydrophobic interaction.

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.