Water‐Soluble Blue Fluorescence‐Emitting Hyperbranched Polysiloxanes Simultaneously Containing Hydroxyl and Primary Amine Groups

Clustering-Triggered Emission Mechanism of Sulfur Ester-Polyacrylamide Aqueous Solution

Most nonconventional luminogens enjoy good water solubility and biocompatibility, showing unique application prospects in fields like biological imaging. Although clustering-triggered emission (CTE) mechanisms have been proposed to explain such emissions, it has not been thoroughly elucidated, which limits their development and application. Herein, the photoluminescence properties of polyacrylamide prepared by reversible addition-fragmentation chain transfer (RAFT) polymerization aqueous solution are utilized to further investigate the effects of changes in concentration, in order to elucidate the emission mechanism through transmission electron microscopy (TEM), small angle X-ray scattering (SAXS) and theoretical calculation. The results showed that the size distribution, morphology, and distance between the polymer clusters formed in the water solution are successfully correlated with the cluster emission centers. The emission mechanism of nonconventional luminogens solutions is more clearly and intuitively elucidated, which has a promoting effect on the emission and application of this field. It provides a strategy a strategy to clarify the CTE mechanism of nonconventional luminogens solution more clearly.

Controllable Blue Shift and Enhancement Emission during the Gradually Increasing Molecular Weight of Polyacrylamide

Nonconventional luminescent polymers have become research hotspots due to their advantages such as persistent room temperature phosphorescence (p-RTP) emission and strong film-forming properties. It is proven that the molecular weight (MW) of such luminescent polymers has a significant impact on their emission over a large range, generally with a red shift as the MW increases. Herein, four controllable MW polyacrylamides are prepared via reversible addition-fragmentation chain transfer polymerization (RAFT), and their photoluminescence quantum yield and p-RTP lifetimes gradually increase with the increasing MW. The emission of p-RTP gradually shifts blue with increasing MW, which is likely due to the gradually changing interactions between the electron-rich portion in RAFT reagent and the increasing acrylamide (AM) units in the molecular chain. These can be reasonably explained through small angle X-ray scattering, the clustering-triggered emission (CTE) mechanism, and supported by theoretical calculations. Powder with controllable p-RTP capability has the potential for strategic anti-counterfeiting encryption. The above results not only promote the development of the CTE mechanism toward more precise explanations but also provide new ideas for the preparation of nonconventional luminescent polymers with controllable p-RTP emission performance.

Recent progress on polymerization-induced emission

The aggregate luminescence behaviors of polymeric luminescent materials have been attracting great attention. However, the importance of the polymerization process on luminescence, namely, polymerization-induced emission (PIE), has rarely been overviewed. In this review, recent advances in polymerization with PIE effects are summarized, including PIE with aromatic rings based on one-/two-/multi-component polymerizations, and PIE without aromatic rings according to disparate mechanisms of polymerizations. Typical examples are selected to elaborate the basic design principles, as well as the properties and potential applications of the luminous polymers. Moreover, the challenges and perspectives in this area are also discussed.

Nonconventional Luminescent Piperazine-Containing Hyperbranched Polysiloxanes with Pure n-electron

Nonconventional luminogens with high quantum yield (QY) possess very potential applications in various fields. However, the preparation of such luminogens remains a great challenge. Herein, the first example of piperazine-containing hyperbranched polysiloxane exhibiting blue and green fluorescence is reported under the irradiation of different excitation wavelength and a high QY of 20.9%. The density functional theory (DFT) calculations and experimental results revealed that the through-space conjugation (TSC) within the clusters of N and O atoms is produced via the induction of multiple intermolecular hydrogen bonds and flexible SiO units, which is accountable for the fluorescence. Meanwhile, the introduction of the rigid piperazine units not only rigidifies the conformation, but also enhances the TSC. In addition, the fluorescence of both P1 and P2 shows concentration-, excitation-, and solvent-dependent emission, especially exhibits significant pH-dependent emission and obtains an ultrahigh QY of 82.6% at pH 5. The synthetic luminogens show excellent applications in fluorescence detection for Fe3+ and Co2+ , information encryption, and fluorescent film. This study provides a novel strategy to rationally design high-efficiency nonconventional luminogens.

Clustering-enhanced, nonconventional photoluminescence from a silicone surfactant

By using the intrinsic nonconventional photoluminescence (n-PL) of organo-siloxane and the synergetic effect of the surfactant mixture, we report strong n-PL from aqueous colloids containing a nonionic silicone surfactant mixed with a traditional anionic surfactant, with an unprecedently high fluorescence quantum yield of up to 85.58%.

Organosilicon Fluorescent Materials

In the past few decades, organosilicon fluorescent materials have attracted great attention in the field of fluorescent materials not only due to their abundant and flexible structures, but also because of their intriguing fluorescence properties, distinct from silicon-free fluorescent materials. Considering their unique properties, they have found broad application prospects in the fields of chemosensor, bioimaging, light-emitting diodes, etc. However, a comprehensive review focusing on this field, from the perspective of their catalogs and applications, is still absent. In this review, organosilicon fluorescent materials are classified into two main types, organosilicon small molecules and polymers. The former includes fluorescent aryl silanes and siloxanes, and the latter are mainly fluorescent polysiloxanes. Their synthesis and applications are summarized. In particular, the function of silicon atoms in fluorescent materials is introduced. Finally, the development trend of organosilicon fluorescent materials is prospected.

High-Efficiency Long-Wavelength Fluorescent Hyperbranched Polysiloxanes: Synthesis, Emission Mechanism, Information Encryption, and Film Preparation

Unconventional fluorescent polymers possess the advantages of excellent biocompatibility, environmental friendliness, and facile structural regulation; however, such polymers usually have low fluorescence intensity and quantum yields in the long-wavelength range. In this work, three kinds of high-efficiency long-wavelength emissive hyperbranched polysiloxanes are obtained by introducing aromatic amino acids. These functionalized hyperbranched polysiloxanes have high fluorescence intensity and quantum yields in green, yellow, and red emission regions. Experimental results and density functional theory calculations reveal that the long-wavelength emission comes from the enhanced electronic communication among the conjugated π bonds, electron-rich atoms, and -Si(O)₃ and other functional groups. Especially, the conjugated π bonds efficiently enlarge the spatial electronic delocalizations, resulting in the high-efficiency long-wavelength emission. Moreover, the prepared polymers show excellent applications in information encryption and film preparation. This work could serve as a guide to develop high-efficiency long-wavelength unconventional fluorescent polymers.

Truly Multicolor Emissive Hyperbranched Polysiloxane: Synthesis, Mechanism Study, and Visualization of Controlled Drug Release

Unconventional fluorescent polymers have attracted increasing attention due to their facile synthesis, excellent biocompatibility, and novel photophysical properties. In this work, a truly multicolor emissive hyperbranched polysiloxane (HBPSi-β-CD) is obtained through adjusting the distribution of electron-rich atoms and grafting β-cyclodextrin; the quantum yields of HBPSi-β-CD after being excited by 360, 420, 450, and 550 nm are 19.36, 31.46, 46.14 and 44.84%, respectively. The density functional theory calculations reveal that the truly multicolor emission is derived from the formed electron delocalization among the hydroxyl, amine, ether, and -Si(O)₃ groups due to the strong intermolecular interaction, high density of electron-rich atoms, and low steric hindrance among functional groups. The prepared polymers could serve as a multisensitivity sensor in detecting Fe³⁺, Cu²⁺, and Co²⁺. The HBPSi-β-CD shows low cytotoxicity and excellent cellular imaging capability. The self-assembly of HBPSi-β-CD also possesses high drug loading capacity and pH-controlled drug release, especially, the drug delivery system could be applied in the visualization of controlled drug delivery.

Nonconventional luminophores: characteristics, advancements and perspectives

Nonconventional luminophores devoid of remarkable conjugates have attracted considerable attention due to their unique luminescence behaviors, updated luminescence mechanism of organics and promising applications in optoelectronic, biological and medical fields. Unlike classic luminogens consisting of molecular segments with greatly extended electron delocalization, these unorthodox luminophores generally possess nonconjugated structures based on subgroups such as ether (-O-), hydroxyl (-OH), halogens, carbonyl (CO), carboxyl (-COOH), cyano (CN), thioether (-S-), sulfoxide (SO), sulfone (OSO), phosphate, and aliphatic amine, as well as their grouped functionalities like amide, imide, anhydride and ureido. They can exhibit intriguing intrinsic luminescence, generally featuring concentration-enhanced emission, aggregation-induced emission, excitation-dependent luminescence and prevailing phosphorescence. Herein, we review the recent progress in exploring these nonconventional luminophores and discuss the current challenges and future perspectives. Notably, different mechanisms are reviewed and the clustering-triggered emission (CTE) mechanism is highlighted, which emphasizes the clustering of the above mentioned electron rich moieties and consequent electron delocalization along with conformation rigidification. The CTE mechanism seems widely applicable for diversified natural, synthetic and supramolecular systems.

Disulfide-Containing Polysiloxane with Multicolor Fluorescence and Visible-Light Excitation: Design, Synthesis, and Mechanism Exploration

Aggregation-induced emission (AIE) polysiloxane has attracted growing attention in recent years due to its outstanding biocompatibility. However, polysiloxane usually requires high-energy UV light for excitation and exhibits monochromatic blue emission. Moreover, the experimental selection process of polysiloxane with designed features is time-consuming and laborious. So, in this paper, we developed a new molecular structure selection strategy using theoretical calculations instead of experiments, and a linear disulfide-containing polysiloxane (L1) is selected and synthesized. To our surprise, L1 can be excited by low-energy visible light (Ex = 508 nm and Em = 588 nm) and emit multicolor fluorescence under different excitation wavelengths. A further study of the luminescence mechanism was carried out through calculations about the quantum states of L1. Moreover, L1 shows multiple stimuli-responsiveness, such as redox, pH, metal ions, and solvent. This work provides an integrated route for the molecular design of macromolecular AIE luminogens with attractive fluorescence properties.

Hydrogen Bonding-Derived Healable Polyacrylate Elastomers via On-demand Copolymerization of n-Butyl Acrylate and tert-Butyl Acrylate

Achieving a desirable combination of good mechanical properties and healing efficiency is a great challenge in the development of self-healing elastomers. Herein, a class of tough and strong self-healing polyacrylate elastomers (denoted as HPs) was developed simply by free-radical copolymerization of n-butyl acrylate (nBA) and tert-butyl acrylate (tBA) and a subsequent hydrolysis reaction rather than direct copolymerization of nBA and acrylic acid (AA). The tiny difference in reactivity between nBA and tBA makes the structural units of the copolymer easy to control. Precise regulation of molecular composition can be realized just by varying the relative monomer content, making its mechanical properties to vary from ductile to robust. Strikingly, when HP samples are cut off within the gauge length, they can heal into coherent and smooth samples and recover at least 79% of the original strength. Hydrogen bond interactions serve as physical cross-linking points, contributing to the high mechanical performance (fracture energy of up to 73.78 MJ·m^-3 and tensile strength of up to 17.80 MPa) as well as shape memory function. Moreover, the HP samples emit strong fluorescence when exposed to a 365 nm UV lamp and exhibit an aggregation-enhanced emission effect in the state of dissolution.

Energy-Transfer-Induced Multiexcitation and Enhanced Emission of Hyperbranched Polysiloxane

Fluorescent hyperbranched polysiloxane (HBPSi) has attracted increasing attention due to its good biocompatibility. However, its emission mechanism remains an open question. Unfortunately, the excitation spectra of HBPSi are rarely systematically investigated and show a narrow excitation band, which hinders the emission mechanism study. Herein, we synthesized a series of novel HBPSi containing l-glutamic acid (HBPSi-GA). Surprisingly, these polymers have four excitation peaks and two emission peaks, which are caused by the energy transfer from free functional groups to heterogeneous electron delocalizations in different clusters. Meanwhile, the fluorescence and biocompatibility of HBPSi-GA are significantly improved with increasing l-glutamic acid. Furthermore, HBPSi-GA exhibits dual stimuli-responsive fluorescence to temperature and Fe³⁺ as well as potential application in cell imaging. This research possesses important guidance to develop multiexcitation unconventional fluorescent polymers.

Recent advances in the development and applications of nonconventional luminescent polymers

Recently, nonconventional luminescent polymers (NLPs) have emerged as the most sought-after alternative luminescent materials. This review provides a thorough description of the importance and applications of each class of state-of-the-art NLPs.

Clustering-Triggered Emission of Nonconjugated Polyacrylonitrile

Intrinsic emission from nonconjugated polymers has attracted considerable attention owing to its fundamental importance and intensive applications in diverse fields. The emission mechanism, however, is still in debate. Herein, nonconjugated polyacrylonitrile (PAN) molecules are found to be virtually nonluminescent in dilute solutions, while being highly emissive when concentrated or aggregated as nanosuspensions, solid powders, and films, exhibiting distinct aggregation-induced emission (AIE) characteristics. Moreover, triplet emissions of delayed fluorescence and room temperature phosphorescence are detected from the solid powders. Such unique emission of nonconjugated PAN is ascribed to the formation of cyano clusters, which act as the exact chromophores. In these clusters, through space electronic interactions, namely overlap of π and lone pair (n) electrons among cyano groups extend the conjugation and meanwhile rigidify the molecular conformations, thus offering remarkable emission upon irradiation. The AIE phenomenon can also be well rationalized by the formation of cyano clusters together with conformation rigidification. And the triplet emissions shall be originated from the n-π* transition owing to the presence of lone pairs. It is believed that such clustering-triggered emission mechanism is instructive for further development of unorthodox luminogens.

Facile one-pot synthesis of novel water-soluble fluorescent hyperbranched poly(amino esters)

Two kinds of water-soluble fluorescent hyperbranched poly(amino esters) were first synthesized by a convenient one-pot approach via the A₂ + B₃ Michael addition reaction of trimethylolpropane triacrylate and aliphatic diamines.

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.

Unanticipated bright blue fluorescence produced from novel hyperbranched polysiloxanes carrying unconjugated carbon–carbon double bonds and hydroxyl groups

Bright blue fluorescence-emitting hyperbranched polysiloxane simultaneously carrying unconjugated carbon–carbon double bonds and hydroxyl groups is reported for the first time.

Sulfonated ethylenediamine–acetone–formaldehyde condensate: preparation, unconventional photoluminescence and aggregation enhanced emission

The water-soluble sulfonated ethylenediamine–acetone–formaldehyde (SEAF) with unconventional fluorescence and AEE effect was prepared. The emission mechanism was ascribed to the cluster-induced emission of carbonyl groups.