Aggregation-enhanced Emission Properties Research Articles

Organoplatinum Complex Exhibiting Aggregation-Enhanced Emission (AEE) and Dual-Channel Ion-Sensing Properties by Terminating the Molecular Configuration Transformation (MCT) and Excited-State Intramolecular Proton Transfer (ESIPT).

Emitters produce weak emissions when they undergo structural changes such as molecular configuration transformation (MCT) or excited-state intramolecular proton transfer (ESIPT) but give out strong emissions after terminating these distortions. Herein, an organoplatinum complex, Pt-ppy-ABP, carrying a salicylaldehyde-based Schiff base unit is synthesized. It exhibits weak emission in dilute solutions but shows bright emission at the aggregated state or after interacting with F- and Zn2+. This suggests that it has an aggregation-enhanced emission (AEE) property and holds potential in ion detection. Supported by theoretical calculations and femtosecond transient absorption results, this complex suffers excited-state structural changes including MCT from a square-planar configuration to a tetrahedral one, as well as intramolecular rotation of a monodentate ligand and ESIPT, showing weak emission in its solutions. At the aggregated state, it releases strong yellow emissions because of the restraints of MCT and ligand rotation. Upon interacting with F- or Zn2+, it emits bright-red or -green emissions, achieving detection limits of 10-7 M. The sensing mechanism is concluded as deprotonation- and coordination-induced ESIPT terminations, respectively. Given its AEE property and ion-responsive emissions, its application in information encryption is also explored. Finally, these findings should provide valuable clues for the developments of chemosensors with dual-channel recognition abilities.

Pyridinium-Yne Click Polymerization: A Facile Strategy toward Functional Poly(Vinylpyridinium Salt)s with Multidrug-Resistant Bacteria Killing Ability.

Polymeric materials with antibacterial properties hold great promise for combating multidrug-resistant bacteria, which pose a significant threat to public health. However, the synthesis of most antibacterial polymers typically involves complicated and time-consuming procedures. In this study, we demonstrate a simple and efficient strategy for synthesizing functional poly(vinylpyridinium salt)s via pyridinium-yne click polymerization. This click polymerization could proceed with high atom economy under mild conditions without any external catalyst, yielding soluble and thermally stable poly(vinylpyridinium salt)s with satisfactory molecular weights and well-defined structures in excellent yields. Additionally, the incorporation of luminescent units such as fluorene, tetraphenylethylene, and triphenylamine into the polymer backbone confers excellent aggregation-enhanced emission properties upon the resulting polymers, rendering them suitable for bacterial staining. Moreover, the existence of pyridinium salt imparts intrinsic antibacterial activity against multidrug-resistant bacteria to the polymers, enabling them to effectively inhibit wound bacterial infection and significantly expedite the healing process. This work not only provides an efficient method to prepare antibacterial polymers, but also opens up the possibility of various applications of polymers in healthcare and other antibacterial fields.

Chiral binol-[4]helicene hybrids: Strong solid-state organic emitters with aggregation-enhanced emission and chiroptical properties

Chiral organic fluorescent materials have attracted broad attention for their application in various chiroptical devices. Helicenes possess special helical structure and unique optical properties, and have been utilized to develop chiral organic fluorescent materials with excellent chiroptical performance. However, the low luminescence efficiency of helicene-based chiral fluorescent materials in solid state limits their practical applications. In this work, chiral organic fluorescent emitters with helicene moiety have been developed from binaphthanol structure. These BINOL [4]helicene compounds display aggregation-enhanced emission properties, and have strong blue emission in solid state with fluorescent quantum yield up to 0.67. The DFT calculation reveals that these compounds have highly twisted molecular structures. Thus, the excellent fluorescent properties in solid state could be aroused by the highly contorted molecular structures, which could limit the π-π stacking of adjacent molecules in solid state. The enantiomers of these compounds show strong Cotton effects in circular dichroism spectra, and the molecules with 4-methoxy phenyl moiety exhibit circularly polarized luminescence properties.

Synthesis, structural, photo-physical properties and DFT studies of some diarylheptanoids

In the present work, we have described the structures, photo-physical properties and DFT computations of some curcumin type diarylheptanoids (4a–c). These compounds were characterized by multi-spectroscopic techniques including X-ray single crystal of one of the intermediates (3a). The molecular geometries and structural features were configured by DFT -B3LYP/6-31G(d,p) calculations; however, combined 6-31G(d,p)/LANL2Dz basis sets (B3LYP/Gen) were employed in case of bromine and iodine derivatives. Compared to the native curcuminoids, these diarylheptanoids showed blue-shifted optical spectroscopic features in solution; aggregation enhanced emission properties were also noted. The incorporation of halogen atom enhanced thermal stability of the compounds. Aided by Cartesian coordinate displacement of the computed wavenumbers, we have suggested reliable vibrational assignments for the observed infrared fundamentals. The results of this study will be a valuable addition to the growing body of work on the properties of curcuminoids.

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.

Effects of fused rings linked to the 2,5-position of pyrrole derivatives with near-infrared emission on their aggregation-enhanced emission properties

Pyrrole derivatives with NIR emission and AEE properties were synthesized through introducing different fused rings and a furanylidene group.

An AEE-active probe combined with cyanoacrylate fuming for a high resolution fingermark optical detection

Latent fingermark imaging plays an important role in forensic investigation. The choice of an appropriate method and reagent is essential for acquiring high quality fingermark images. In this work, a push-pull structure NIFA of a fluorene (π-conjugated) core substituted with 1,8-naphthalimide (electron-attracting group) and anthracene (electron-donating group) was fabricated, which provided an aggregation-enhanced emission (AEE). The photophysical and AEE properties of NIFA were investigated by experimental and theoretical studies. This dye can emit bright blue to blue-green fluorescence. The results showed that the intramolecular charge transfer from the fluorene part to the 1,8-naphthalimide part dominated the luminescence of NIFA. The combined utilization of cyanoacrylate glue fuming and a NIFA fluorescent imaging technique can image the fine structure of fingermark from the first level to the third level. After investigating the interaction mechanism between cyanoacrylate glue and NIFA, we found that the hydrophobic-hydrophobic interaction was in charge of the fingermark imaging quality enhancement. All results proved that this AEE active fluorescent probe combined with cyanoacrylate fuming could supply a new method for latent fingermark fluorescent detection.

Two-step separation-free quantitative detection of HSA and FIB in human blood plasma by a pentaphenylpyyrrole derivative with aggregation-enhanced emission properties

A novel fluorescence based strategy, employing the aggregation-enhanced emission (AEE) property of sodium 4,4′,4”-(3,4-diphenyl-1H-pyrrole-1,2,5-triyl)tribenzoate (DP-TPPNa), was proposed to determine the concentrations of human serum albumin (HSA) and fibrinogen (FIB) in human plasma without separation required. HSA level was determined at concentrations lower than 110μg/mL by the selective PL response of DP-TPPNa to HSA and FIB was quantified at high HSA concentrations in the range of 140–200μg/mL by the synergistic effects of FIB and HSA on the PL intensity of DP-TPPNa. Compared with authoritative instruments, the method developed in the present work is rapid, simple, extremely sensitive, highly selective and precise for the quantitative detection of proteins with one single system, which is an ideal detection system candidate for the early diagnosis of diseases. The results also indicate that the interactions between proteins can affect their configuration and conformation blood plasma. This can be used to study the correlations among the serum components.

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.

Conjugated polymers with carbazole, fluorene, and ethylene dioxythiophene in the main chain and a pendant cyano group: Synthesis, photophysical, and electrochemical studies

ABSTRACTSix new conjugated polymers comprising of carbazole, fluorene, and ethylene dioxythiophene (EDOT) moieties along the backbone with a pendant cyano group attached to the ethylene moiety have been designed and synthesized via Sonogashira coupling polymerization reaction. Optical and electrochemical characterizations have shown that the energy band gaps lie within the range of 2.35–2.44 eV. Additionally, the presence of carbazole and EDOT makes these polymers better hole transporting materials, which is reflected from their low oxidation potential peaks (0.55–1.11 V) in cyclic voltammograms. Furthermore, the aggregation enhanced emission (AEE) phenomenon resulted in a 2.6‐fold increase in fluorescence intensity in a 90:10 THF/water mixture in comparison to pristine THF. The AEE properties were further verified by DLS (dynamic light scattering) experiment and SEM (scanning electron microscopy) studies. Polymers in solution as well as in polystyrene matrix emit in the green region (quantum yield in solution state Φf =41–43%) with CIE values (0.25–0.36, 0.52–0.57). Excellent thermal stability is observed for the new polymers. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 2774–2784

Synthesis, structure and optical properties of tetraphenylethene derivatives with through-space conjugation between benzene and various planar chromophores

A series of tetraphenylethene derivatives with through-space conjugation and aggregation-enhanced emission properties are synthesized and studied.

Nonconventional photoluminescence from sulfonated acetone–formaldehyde condensate with aggregation-enhanced emission

The fluorescence and aggregation-enhanced emission property of sulfonated acetone–formaldehyde condensate (SAF) with a nonconventional chromophore is reported.

Crystallization-promoted emission enhancement of poly(l-lactide) containing a fluorescent salicylideneazine center with aggregation-enhanced emission properties

AEE-active 1,2-bis(2,4-dihydroxybenzylidene)hydrazine initiates polymerization of lactide monomer, resulting in polylactides containing an AEE-active center.

Red fluorescent luminogen from pyrrole derivatives with aggregation-enhanced emission for cell membrane imaging.

A dye emitted red fluorescence with aggregation-enhanced emission properties was reported here. It can be utilized to specifically recognize the cell membrane of MCF-7 and 293T cell lines during bio-imaging.

Emission enhancement and color adjustment of silicon-cored structure in tetraphenyl benzene with aggregation-enhanced emission

In this paper, we report the synthesis and optical behavior of tetraphenyl benzene and its two derivatives. All the three compounds exhibited aggregation-enhanced emission (AEE) properties at a low concentration. The AEE mechanism was investigated and is due to restricted intramolecular rotation and unique packing structure. Furthermore, this kind of dendritic benzene derivatives exhibited interesting optical properties with increased concentration. Furthermore, we found a new phenomenon that the silicon-cored structure could efficiently enhance emission intensity and adjust the emission colors of dendritic benzene. The phenomenon was called “silicon-cored effect.” This effect may give some guidance to the design of new luminescent materials with AIE and AEE properties.

Effect of vinylene bond geometry on the molecule packing and aggregation-enhanced emission property of a pair of 1-[(9-anthracenyl)vinyl]pyrene isomers

A new pair of 1-[(9-anthracenyl)vinyl]pyrene (AVP) isomers was simultaneously obtained in a ratio of about 10:1. They cannot be separated by chromatography. However, they can be more effectively separated via sublimation. Both isomers display an aggregation-induced enhanced emission character, which is mainly due to a large increase in the radiative decay rate. The vinylene bond geometry brings different packing motifs. The interacting adjacent molecules in trans-AVP crystals can adopt both edge-to-face and face-to-face arrangements. In contrast, in cis-AVP crystals the adjacent molecules are inclined to adopt an edge-to-face arrangement. The molecule packing plays an important role in the solid emission efficiency.

Dibutylaminophenyl- and/or Pyridinyl-Capped 2,6,9,10-Tetravinylanthracene Cruciforms: Synthesis and Aggregation-Enhanced One- and Two-Photon Excited Fluorescence

This article reports the synthesis, one- and two-photon absorption (2PA), and emission properties of 2,6,9,10-tetraarylvinylanthracene derivatives in both THF solution and aqueous media. The results show that the center-crossed integration of aggregation-induced emission-active 9,10-diarylvinylanthracenes and aggregation-quenched emission-active 2,6-diarylvinylanthracenes does not surely constitute aggregation-enhanced emission (AEE) dyes, and only the dibutylamino-containing cruciforms exhibit AEE effect. The investigation of two-photon properties reveals that the dibutylamino-containing cruciforms show large 2PA cross sections (δmax up to 1500 GM) in both THF solution and THF/water (1/9) mixture, and the two-photon fluorescence action cross sections in aqueous media are about 10 times higher than those in THF solution because of their much higher fluorescence quantum yields in aqueous media. This work has demonstrated that the nature of the building blocks could significantly affect the aggregation behaviors and fluorescence properties of anthracene-centered cruciforms. Cruciforms with excellent 2PA and AEE properties could be constructed by using anthracene as the π-center and suitable aromatic units as building blocks.

Synthesis of two novel indolo[3,2-b]carbazole derivatives with aggregation-enhanced emission property

Luminogenic materials with AIE (aggregation-induced emission) and AIEE (aggregation-induced enhanced emission) characteristics have attracted substantial research interest due to their potential applications in optics, electronics environmental and the biological sciences. Here, we successfully synthesized two novel indolo[3,2-b]carbazole derivatives (compounds 3 and 4) with strong symmetrical groups, which were demonstrated to exhibit superior AIEE properties. Both 3 and 4 contain the same π-conjugated core structure, but slightly differ in the cyano-substituted stilbene group, giving rise to a high charge mobility, similar optical properties and energy band-gaps. The bulky cyano group attached to a vinylene moiety generates intramolecular co-planarity and prevents π–π stacking, whereby the emission in the aggregates can be enhanced. In addition, it is found that the cyano group also plays an important role in the formation of J-type aggregation, which is advantageous to the appearance of AIE and/or AIEE properties. A slight modification of the terminal substituent group renders compounds 3 and 4 AIEE properties entirely. As revealed by crystallographic data, the multiple intermolecular hydrogen bonding in 4 restricts intramolecular vibration and rotation, which enables 4 to emit intensely in the solid state. Moreover, cyano groups endow 3 with an improved self-assembly ability under the proper conditions. The molecules of 3 self-organize into one-dimensional ordered microfibers and/or nanorods that show a significant optical waveguide with different water fractions, indicating that the aqueous suspension of microfibers favors fluorescence emission. Our results demonstrate that the AIEE properties of the novel indolo[3,2-b]carbazole derivatives are highly related to the molecular structure and aggregate packing.