Aggregation-Induced Emission in Tetraphenylthiophene-Derived Organic Molecules and Vinyl Polymer

Aggregation-induced emissive nanoarchitectures for luminescent solar concentrators

Aggregation-induced emission (AIE), the phenomenon by which selected luminophores undergo the enhancement of emission intensity upon aggregation, has demonstrated potential in materials and biomaterials science, and in particular in those branches for which spectral management in the solid state is of fundamental importance. Its development in the area of luminescent spectral conversion devices like luminescent solar concentrators (LSCs) is instead still in its infancy. This account aims at summarizing relevant contributions made in this field so far, with a special emphasis on the design of molecular and macromolecular architectures capable of extending their spectral breadth to the deep-red (DR) and the near-infrared (NIR) wavelengths. Because of the many prospective advantages characterizing these spectral regions in terms of photon flux density and human-eye perception, it is anticipated that further development in the design, synthesis and engineering of advanced molecular and macromolecular DR/NIR-active AIE luminophores will enable faster and easier integration of LSCs into the built environment as highly transparent, active elements for unobtrusive light-to-electricity conversion.

Polymorphism and Light-Driven Forward Movement of TPE Derivative Micro-Crystal due to ArH-pi Interactions Difference

Aggregation-induced emission (AIE) and aggregation-caused quenching (ACQ) are two classes of opposite luminescence phenomena. It is almost impossible to show both AIE and ACQ effect simultaneously by the same molecule. However, here we report that a simple TPE derivative TAP-TPE grows into both AIE crystals and ACQ ones. It is found that equatorial, contact distance-longer and weak ArH-π interactions exist in AIE crystals while vertical, contact distance-shorter and strong ArH-π interactions appear in ACQ crystals. Theoretical calculation of electron density on the interaction atoms unveils that ACQ crystals have much larger change in electron density than AIE ones, suggesting that the intermolecular electron transfer aroused by the strong ArH-π hydrogen bonds leads to ACQ phenomenon. This result provides a new insight into the emission mechanism in aggregation state. Interestingly, due to the ArH-pi interactions difference, only one of five kinds of crystals shows rapid photochromism, and can act as multimode anti-counterfeiting materials. Very exceptionally, for the first time we find that the photochromic micrometric rod-like crystal even makes forward rolling movement as it repeatedly bends and straightens by responding to on and off of the ultraviolet light irradiation, displaying potential for photo-actuator and light-driven micro-vehicle.

Multi Stimuli-Responsive Aggregation-Induced Emission Active Polymer Platform Based on Tetraphenylethylene-Appended Maleic Anhydride Terpolymers

Multi stimuli-responsive aggregation-induced emission (AIE) active polymers have great application prospects in high-tech innovations. Herein, three types of tetraphenylethylene (TPE)-containing monomers were synthesized and utilized in preparing TPE-appended maleic anhydride terpolymers. After hydrolysis, the produced TPE-appended maleic acid terpolymers have identical linear charge densities but different "primary" structures, which created widely varied microenvironments around the carboxylate and TPE groups. Benefiting from the synergistic interaction of the TPE moiety and the terpolymer conformation change, the TPE-appended maleic acid terpolymers exhibited fluorescence changes in response to multi stimuli, including pH, ionic strength, Ca²⁺, and bovine serum albumin. On both the "signaling" and the "stimuli acceptor" sides, the multi stimuli-responsive fluorescence behavior was influenced markedly by the terpolymer primary structure. The fundamental insights gained in the present work are important for developing an efficient and versatile stimuli-responsive AIE-active polymer platform for chemo-sensing, bioimaging, and so on.

A novel AIEE active anti-B18H22derivative-based Cu2+and Fe3+fluorescence off-on-off sensor

A novel fluorescence sensor for successive detection of Cu²⁺and Fe³⁺based on anti-B₁₈H₂₂derivative which possesses 5-hydroxyisoquinoline as an ionophore was synthesized via a one-pot and its structure and photophysical properties were characterized by NMR, HRMS, FTIR, UV-vis, PL and theoretical calculation. The fluorophore displays two emission peaks at 460 nm and 670 nm in THF solution coming from the emission of the locally excited state and intramolecular charge transfer fluorescence, respectively. The complex exhibited obvious aggregation-induced emission enhancement (AIEE) characteristics in THF/H₂O solution by increasing the aqueous concentration from 70% to 95%. The AIEE molecules showed a high selectivity towards Cu²⁺over other metal ions by forming a 2:1 metal-to-ligand complex in THF/H₂O (fw = 20%) solution, the fluorescence intensity increased as a linear function of the Cu²⁺concentration at 460 nm due to the inhibition of PET effect. The fluorescent emission was quenched linearly by the addition of Fe³⁺, which provides a method for successive determination of Cu²⁺and Fe³⁺based on 'off-on-off' fluorescence of the fluorescent. The detection limit of Cu²⁺and Fe³⁺was 5.7 × 10^-6M and 7.2 × 10^-5M respectively. Morever, a rapid identification of Cu²⁺in the aqueous solution by naked eyes can be realized. In addition, the molecules were pH-sensitive, the fluorescence quenching can be observed in strongly alkaline environment. The method has been applied to the determination of copper ions in water samples with satisfactory results.

An AIE active BODIPY based fluorescent probe for selective sensing of Hg2+ via dual mechanism PET and CHEF

A pyrazole appended BODIPY ligand (L) is synthesized and thoroughly characterized by various spectroscopic studies (1H, [Formula: see text]C, [Formula: see text]B, [Formula: see text]F, ESI–MS, UV-vis and fluorescence). The ligand (L) displays aggregation induced emission (AIE) in solution (a mixture of CH3OH and water) and solid state. The vital role of the restriction of intramolecular rotation (RIR) in AIE is supported by viscosity experiments and fluorescence lifetime studies. Photophysical behaviour and aggregate morphology is investigated by UV-vis, emission and scanning electron microscopy (SEM). Multiple strong intermolecular hydrogen bonds (C–H[Formula: see text]N and C–H[Formula: see text]F) play a significant role in the AIE response. In addition, L shows strong sensitivity toward Hg[Formula: see text]ion via chelation induced enhanced fluorescence (CHEF) mechanism. Job’s plot analysis suggested a 1:1 binding stoichiometry between L and Hg[Formula: see text], which has been further supported by electrospray ionization mass spectrometry and density functional theory.

Room-Temperature Synthesis of Tetrasubstituted 1,3-Dithioles by Dimerizing Sulfuration of Chalcones with Elemental Sulfur

Chalcones were found to undergo sulfurative dimerization with elemental sulfur to tetrasubstituted 1,3-dithioles. The reaction was found to proceed at room temperature in the presence of a nitrogen-base catalyst in DMSO.

Coumarin–tetraphenylethylene regioisomers: synthesis, photophysical and aggregation-induced emission properties

Coumarin–tetraphenylethylene (CTPE) regioisomers with different linkage types and substitution positions (coumarin C5, C6, C7) were synthesized, characterized, photophysical and aggregation-induced emission properties reported.

Chlorine (Cl) - Substituted Carbazole Based A-π-D-π-a Push-Pull Chromophores as Aggregation Enhanced Emission (AEE) Active Viscosity Sensors: Synthesis, DFT and NLO Approach

Three new carbazole functionalized A-π-D-π-A extended chromophores 4a, 4b and 4c comprising of different chemical functional groups on C=C bond with the assistance of chlorovinylene group in π-conjugation are synthesized and investigated spectroscopically. We have investigated the effect of different electron acceptors - carboxycyanomethylene, dicyanomethylene and 2-(benzothiazol-2-yl) cyanomethylene, the effect of the insertion of chlorine in π-conjugation on photophysical properties and the effect of double acceptors. The chromophores 4a, 4b and 4c exhibited positive solvatochromism with large Stokes shifts and bright orange to red solid-state fluorescence. Amongst all the three compounds 4c exhibited maximum emission wavelength at 615 nm in DMSO. They presented characteristic twisted intramolecular charge transfer (TICT) emission. Observations exhibited that 4c containing long hexyl group in donor unit and 2-(benzothiazol-2-yl) cyanomethylene as an acceptor group formed an aggregate in the mixture of solvents and exhibited better aggregation enhanced emission (AEE) compared to the other two derivatives. Amongst the three styryls, 4c showed the highest emission intensity 299 a.u. at 90% water:DMF fraction (f_w). Chromophores 4a-4c also exhibited good fluorescence response towards viscosity. Among the three fluorescent molecular rotors (FMR), 4c exhibited excellent viscosity sensitivity with x value = 0.687. The Non-linear (NLO) characters are estimated with the help of solvatochromic and computational methods using the functionals, B3LYP and CAM-B3LYP. The dyes showed large "linear polarizability (α_CT)", "first order hyperpolarizability" (β) and "second order hyperpolarizability" (γ) values which show that synthesized styryls can be used as a "NLO" material. The α_CT, β and γ for 4c are found to be the maximum amongst the all three dyes which can be ascribed to the smaller band gap apparent from experimental as well as DFT method.

Peraryl Arsoles: Practical Synthesis, Electronic Structures, and Solid-State Emission Behaviors

2,3,4,5-Tetraaryl-1-phenylarsoles were synthesized by utilizing safely generated diiodophenylarsine and zirconacyclopentadienes. The obtained peraryl arsoles showed aggregation-induced emission (AIE), where intense emission was observed in the solid states (quantum yields up to 0.61), whereas the corresponding solutions were very weakly emissive. The optical and electronic properties were examined by experimental and computational methods. It was elucidated that the aryl groups at the 2,5-positions affected the frontier orbitals and the aromaticity of the arsole core. On the other hand, those at the 1,3,5-positions were perpendicular to the luminophore and effective for a restriction of aggregation-caused quenching. Because the lone pair of the arsenic atom has a sufficient coordination ability due to the low aromaticity of the arsole moiety, a gold(I) chloride complex of 1,2,3,4,5-pentaphenylarsole was synthesized. The complex formation caused a blue shift of the emission from the bare ligand. Interestingly, the complex showed luminescent mechanochromism; grinding the crystals with a blue emission (λ_em =445 nm) gave amorphous samples with a greenish-blue emission (λ_em =496 nm).

Tacticity effects in side-chain photoluminescent polymers

A significant red shift (or blue shift) can be observed by increasing the degree of isotacticity (or syndiotacticity).

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.

Investigation of aggregation induced emission in 4-hydroxy-3-methoxybenzaldehyde azine and polyazine towards application in (opto) electronics: synthesis, characterization, photophysical and electrical properties

An azine monomer 4-hydroxy-3-methoxybenzaldehyde azine was synthesized by refluxing with ethanolic solution of vanillin with hydrazine hydrate. It was then converted into polyazine by oxidative polymerization. The structure of azine and polyazine was characterized by FT-IR, UV–visible, ¹H-NMR and ¹³C-NMR. Spectral results suggest the formation of polymer, through C–C and C–O–C coupling of the phenylene and oxyphenylene. The relationship between the structures and photophysical properties of azine and polyazine was studied. Both azine and polyazine show, aggregation induced emission with increase in concentration in DMSO solution. The single crystal structure of azine suggesting the various inter and intra molecular interactions rigidify the conformation and locked the intramolecular rotations of the phenyl rings in the molecule. The inhibition of intramolecular rotation, J- aggregation and increase of conjugation impart the fluorescence in aggregated state. Additionally, the electronic properties namely orbital energies and resulting energy gap calculated theoretically by density functional theory (DFT).

Polymeric AIE-based nanoprobes for biomedical applications: recent advances and perspectives

The development of polymeric luminescent nanomaterials for biomedical applications has recently attracted a large amount of attention due to the remarkable advantages of these materials compared with small organic dyes and fluorescent inorganic nanomaterials. Among these polymeric luminescent nanomaterials, polymeric luminescent nanomaterials based on dyes with aggregation-induced emission (AIE) properties should be of great research interest due to their unique AIE properties, the designability of polymers and their multifunctional potential. In this review, the recent advances in the design and biomedical applications of polymeric luminescent nanomaterials based on AIE dyes is summarized. Various design strategies for incorporation of these AIE dyes into polymeric systems are included. The potential biomedical applications such as biological imaging, and use in biological sensors and theranostic systems of these polymeric AIE-based nanomaterials have also been highlighted. We trust this review will attract significant interest from scientists from different research fields in chemistry, materials, biology and interdisciplinary areas.

Tetraphenylpyrazine-based AIEgens: facile preparation and tunable light emission

Research on aggregation-induced emission (AIE) has been a hot topic. Due to enthusiastic efforts by many researchers, hundreds of AIE luminogens (AIEgens) have been generated which were mainly based on archetypal silole, tetraphenylethene, distyrylanthracene, triphenylethene, and tetraphenyl-1,4-butadiene, etc. To enlarge the family of AIEgens and to enrich their functions, new AIEgens are in high demand. In this work, we report a new kind of AIEgen based on tetraphenylpyrazine (TPP), which could be readily prepared under mild reaction conditions. Furthermore, we show that the TPP derivatives possess a good thermal stability and their emission could be fine-tuned by varying the substituents on their phenyl rings. It is anticipated that TPP derivatives could serve as a new type of widely utilized AIEgen, based on their facile preparation, good thermo-, photo- and chemostabilities, and efficient emission.

Complex from ionic β-cyclodextrin polyrotaxane and sodium tetraphenylthiophenesulfonate: restricted molecular rotation and aggregation-enhanced emission

Because restricted intramolecular rotation (RIR) is the main mechanism responsible for the aggregation-enhanced emission (AEE), we thus used a rigid polyrotaxane to impose effective RIR for an water-soluble and AEE-active luminogen of TPS.

Tetraaryl pyrazole polymers: versatile synthesis, aggregation induced emission enhancement and detection of explosives

Here we report a new approach to obtain tetraaryl pyrazole polymers by free radical polymerization of styryl substituted pyrazole monomers.

N-type pyrazine and triazole-based luminogens with aggregation-enhanced emission characteristics

N-type pyrazine and triazole-based AIEgens that could readily form red-emissive complexes with triphenylamine in the aggregate state were facilely prepared by click reactions.

Luminescent polymers and blends with hydrogen bond interactions

Intermolecular hydrogen bonds are effective forces in hampering molecular rotation and in enhancing emission of luminogenic polymers and blends with aggregation-induced emission property.

Influence of the number and substitution position of phenyl groups on the aggregation-enhanced emission of benzene-cored luminogens

The influence of the number and substitution position of phenyl groups on the emission of benzene-cored AIEgens is unambiguously revealed.

Synthesis of SF5-containing benzisoxazoles, quinolines, and quinazolines by the Davis reaction of nitro-(pentafluorosulfanyl)benzenes

Meta- or para-nitro-(pentafluorosulfonyl)benzenes underwent the Davis reaction with arylacetonitriles to provide the SF₅-containing benzisoxazoles. Good yields were obtained with arylacetonitriles containing the electron-neutral or electron-donor group, while those with the electron-acceptor group were found to be unreactive. Reductions of the benzisoxazoles gave ortho-aminobenzophenones in high yields. Their synthetic utility was demonstrated by condensation reactions with carbonyl compounds or amines to provide SF₅-containing quinolines and quinazolines, respectively.

Complexation of fluorescent tetraphenylthiophene-derived ammonium chloride to poly(N-isopropylacrylamide) with sulfonate terminal: aggregation-induced emission, critical micelle concentration, and lower critical solution temperature

Amphiphilic polymers with hydrophilic poly(N-isopropylacylamide) (PNIPAM) shell connecting hydrophobic tetraphenylthiophene (TP) core, which has the novel aggregation-induced emission (AIE) property, by ionic bonds were prepared to explore the AIE-operative emission responses toward critical micelle concentration (CMC) and lower critical solution temperature (LCST). To exercise the idea, ammonium-functionalized TP2NH(3)(+) and sulfonate-terminated PNIPAM were separately prepared and mixed in different molar ratios to yield three amphiphilic TP-PNIPAMn complexes for the evaluations of CMC and LCST by fluorescence responses. The nonemissive dilute aqueous solutions of TP-PNIPAMn became fluorescent when increasing concentrations above CMC. Heating micelles solution to temperatures above LCSTs causes further enhancement on the emission intensity. The fluorescence responses are explained by the extent of aggregation in the micelles and in the globules formed at room temperature and at high temperatures, respectively.

Self-Scrolling Nanotubular Structure of Amorphous Vinyl Polymer Containing Tetraphenylthiophene-quinoline Pendant Groups

In this communication, we report a scroll-like nanotubular structure found in an amorphous vinyl polymer of PS-Qu containing fluorescent tetraphenyl-quinoline (TP-Qu) pendant groups. By spin-casting dilute solution of PS-Qu, long nanoribbons with heights in correlated to the molecular width of TP-Qu pendant groups formed. On the contrast, single-, double-, and multiple-walled nanoscrolls are the major structures existing in the products from the slow-evaporation process. Presumably, scrolling of nanoribbons result in the scroll-like nanotubular structures with the resolved layer thickness in dimension close to molecular width of the TP-Qu pendant. Computer simulation on the single PS-Qu chain suggests the existence of a straight-chain backbone, with most of the vicinal 1,3-disubstituted TP-Qu groups positioned in near face-to-face arrangements. Intermolecular distances evaluated from the SAEDs were approached by the molecular dynamic of two straight-chain polymer backbones. Favorable π-π interactions among the vicinal 1,3-disubstitued TP-Qu groups are suggested to be a major factor leading to the straight-chain backbone and the observed nanoribbons and nanoscrolls.