Two-photon excitation provides a means of activating chemical or physical processes with high spatial resolution in three dimensions and has made possible the development of three-dimensional fluorescence imaging, optical data storage, and lithographic microfabrication. These applications take advantage of the fact that the two-photon absorption probability depends quadratically on intensity, so under tight-focusing conditions, the absorption is confined at the focus to a volume of order λ3 (where λ is the laser wavelength). Any subsequent process, such as fluorescence or a photoinduced chemical reaction, is also localized in this small volume. Although three-dimensional data storage and microfabrication have been illustrated using two-photon-initiated polymerization of resins incorporating conventional ultraviolet-absorbing initiators, such photopolymer systems exhibit low photosensitivity as the initiators have small two-photon absorption cross-sections (δ). Consequently, this approach requires high laser power, and its widespread use remains impractical. Here we report on a class of π;-conjugated compounds that exhibit large δ (as high as 1, 250 × 10−50 cm4 s per photon) and enhanced two-photon sensitivity relative to ultraviolet initiators. Two-photon excitable resins based on these new initiators have been developed and used to demonstrate a scheme for three-dimensional data storage which permits fluorescent and refractive read-out, and the fabrication of three-dimensional micro-optical and micromechanical structures, including photonic-bandgap-type structures.

Two-photon polymerization initiators for three-dimensional optical data storage and microfabrication

The "click" trick: Many reactions are classified as click reactions even though some are limited to certain applications. Thus, there is danger that the term "click" will become meaningless over time and simply a synonym for "successful". To prevent this, the original click criteria are evaluated in this Essay specifically for the synthetic polymer field and a set of criteria are specified that distinguishes click from other efficient reactions. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

"Clicking" polymers or just efficient linking: What is the difference?

The evolution of self-healing polymers has resulted in a myriad of healing designs that have given way to complex systems capable of supporting multiple cycles, among other features. This progression enables us to propose the implementation of a timeline that classifies self-healing polymers in generations based on the healing mechanism, and correlated with historical development. The first generation employed the encapsulation of external healing agents; the second one, based on intrinsic mechanisms, applied reversible chemistries; and the third generation was inspired by natural examples such as plants and human skin, in which the healing agent is embedded in vascular networks. Despite great efforts and, with a few exceptions, polymers with high healing efficiency and high mechanical performance are not common. To improve this situation, a combination of different mechanisms is currently emerging, giving birth to the fourth generation of self-healing materials. This article, focused on self-healing elastomers, provides a rigorous overview of this new generation, in which the combination of covalent bonds and non-covalent interactions provides an optimal balance between mechanical performance and repairability. The implementation of this concept leads to materials with real commercial potential in functional applications, such as coatings, sensors, actuators, controlled release of drugs, seals, gaskets, hoses, and even high-performance applications such as tires and railway components.

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Evolution of self-healing elastomers, from extrinsic to combined intrinsic mechanisms: a review

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 (CO), carboxyl (–COOH), cyano (CN), thioether (–S–), sulfoxide (SO), sulfone (OSO), 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.

Nonconventional luminophores: characteristics, advancements and perspectives.

Cage-like silsesquioxanes are considered to be ideal and versatile building blocks of hybrid materials due to their unique structures and excellent performance. This Perspective highlights recent advances in the field of cage-like silsesquioxane-based hybrid materials, ranging from monomer functionalization and materials preparation to application. The existing issues are reviewed and the challenges and prospects in this field are also discussed for further development and exploitation.

Cage-like silsesquioxanes-based hybrid materials.

PDMS is biocompatible, economically viable, transparent, and facile to handle and thus is suitable for fluorescent microscopy and biological research. However, there has been no report about polysiloxane-based fluorescent probes applied in bioimaging. In this report, a two-photon polysiloxane-based reversible luminescent probe (P1) was fabricated for the first time. P1 is a powerful tool for detecting the ClO–/GSH cycle in situ both in live cells and in zebrafish. This work demonstrates the potential of polysiloxane-based fluorescent probes for versatile in vivo or in vitro applications in the future.

Binding Reaction Sites to Polysiloxanes: Unique Fluorescent Probe for Reversible Detection of ClO-/GSH Pair and the in Situ Imaging in Live Cells and Zebrafish.

Porous polymers are among the most promising porous materials for various application because they show the combined advantages of fluorescent porous materials and polymers. This study developed a cell imaging technique based on luminescent porous organosilicon polymers (LPOPs) that were synthesized via Friedel-Crafts reaction of octaphenylcyclotetrasiloxane with octavinylsilsesquioxanes. The porous organosilicon polymers possessed narrow pore-size distribution, high surface area, and monomodal nanopores centered at approximately 0.59 nm. The excellent properties to the porous polymers can be attributed to the fine structures of LPOPs. LPOP-2 owned the highest fluorescence intensity and micropore volume ratio in LPOPs and showed high selectivity for Fe3+ detection and excellent sensitivity to nitroaromatic compound detection. Interestingly, these porous polymers still exhibited excellent responsiveness to Fe3+ ion even when inside of living cells. We also fabricated a paper-based sensor using LPOP-2 to develop a simple method for visual detection of explosives. This rapid and visual paper sensor demonstrates promising application for explosive detection and can be expanded for the detection of other analytes.

Siloxane-Based Nanoporous Polymers with Narrow Pore-size Distribution for Cell Imaging and Explosive Detection.

Silicon-assisted unconventional fluorescence from organosilicon materials

AIE-active polysiloxane-based fluorescent probe for identifying cancer cells by locating lipid drops

Step-wise functionalization of polysiloxane towards a versatile dual-response fluorescent probe and elastomer for the detection of H2S in two-photon and NO in near-infrared modes

Zhiming Gou

Papers

Binding Reaction Sites to Polysiloxanes: Unique Fluorescent Probe for Reversible Detection of ClO-/GSH Pair and the in Situ Imaging in Live Cells and Zebrafish.

Siloxane-Based Nanoporous Polymers with Narrow Pore-size Distribution for Cell Imaging and Explosive Detection.

Silicon-assisted unconventional fluorescence from organosilicon materials

AIE-active polysiloxane-based fluorescent probe for identifying cancer cells by locating lipid drops

Step-wise functionalization of polysiloxane towards a versatile dual-response fluorescent probe and elastomer for the detection of H2S in two-photon and NO in near-infrared modes