Luminogenic materials with aggregation-induced emission (AIE) attributes have attracted much interest since the debut of the AIE concept in 2001. In this critical review, recent progress in the area of AIE research is summarized. Typical examples of AIE systems are discussed, from which their structure–property relationships are derived. Through mechanistic decipherment of the photophysical processes, structural design strategies for generating new AIE luminogens are developed. Technological, especially optoelectronic and biological, applications of the AIE systems are exemplified to illustrate how the novel AIE effect can be utilized for high-tech innovations (183 references).

Aggregation-induced emission

Metal–organic frameworks (MOFs) are a unique class of crystalline solids comprised of metal cations (or metal clusters) and organic ligands that have shown promise for a wide variety of applications Over the past 15 years, research and development of these materials have become one of the most intensely and extensively pursued areas A very interesting and well-investigated topic is their optical emission properties and related applications Several reviews have provided a comprehensive overview covering many aspects of the subject up to 2011 This review intends to provide an update of work published since then and focuses on the photoluminescence (PL) properties of MOFs and their possible utility in chemical and biological sensing and detection The spectrum of this review includes the origin of luminescence in MOFs, the advantages of luminescent MOF (LMOF) based sensors, general strategies in designing sensory materials, and examples of various applications in sensing and detection

Luminescent metal–organic frameworks for chemical sensing and explosive detection

Aggregation-induced emission: phenomenon, mechanism and applications.

"United we stand, divided we fall."--Aesop. Aggregation-induced emission (AIE) refers to a photophysical phenomenon shown by a group of luminogenic materials that are non-emissive when they are dissolved in good solvents as molecules but become highly luminescent when they are clustered in poor solvents or solid state as aggregates. In this Review we summarize the recent progresses made in the area of AIE research. We conduct mechanistic analyses of the AIE processes, unify the restriction of intramolecular motions (RIM) as the main cause for the AIE effects, and derive RIM-based molecular engineering strategies for the design of new AIE luminogens (AIEgens). Typical examples of the newly developed AIEgens and their high-tech applications as optoelectronic materials, chemical sensors and biomedical probes are presented and discussed.

Aggregation-Induced Emission: The Whole Is More Brilliant than the Parts

Fluorescent Chemosensors Based on Spiroring-Opening of Xanthenes and Related Derivatives Xiaoqiang Chen, Tuhin Pradhan, Fang Wang, Jong Seung Kim,* and Juyoung Yoon* Departments of Chemistry and Nano Science and of Bioinspired Science (WCU), Ewha Womans University, Seoul 120-750, Korea State Key Laboratory of Materials-Oriented Chemical Engineering, College of Chemistry and Chemical Engineering, Nanjing University of Technology, Nanjing 210009, China Department of Chemistry, Korea University, Seoul 136-701, Korea

Fluorescent chemosensors based on spiroring-opening of xanthenes and related derivatives.

The syntheses, spectroscopic characterizations, and fluorescence quenching efficiencies of polymers and copolymers containing tetraphenylsilole- or silafluorene-vinylene repeat units are reported. These materials were prepared by catalytic hydrosilylation reactions between appropriate monomeric metallole alkynes and hydrides. Trimeric model compounds methyl(tetraphenyl)silole-vinylene trimer (1), methyl(tetraphenyl)silole-silafluorene-vinylene cotrimer (2), and methylsilafluorene-vinylene trimer (3) were synthesized to provide detailed structural and spectroscopic characteristics of the polymer backbone and to assess the extent of delocalization in the luminescent excited state. Poly(tetraphenylsilole-vinylene) (4), poly(tetraphenylsilole-silafluorene-vinylene) (5), and poly(silafluorene-vinylene) (6) maintain a regio-regular trans-vinylene Si−C backbone with possible ground state σ*−π and excited state σ*−π* conjugation through the vinylene bridge between metallole units. Fluorescence spectra of the poly...

Synthesis, Luminescence Properties, and Explosives Sensing with 1,1-Tetraphenylsilole- and 1,1-Silafluorene-vinylene Polymers

The synthesis and spectroscopic characterization of a series of new blue-emitting silafluorene–fluorene copolymers is described. The polymers are synthesized using kinetically controlled hydrosilylation copolymerization of 1,1-dihydridosilafluorene with a series of 9-substituted 2,7-diethynylfluorenes. The polymers contain a trans-only framework with molecular weights in the range of 13 000–20 000, as determined by gel permeation chromatography (GPC) using polystyrene standards, and by 1H NMR spectroscopy using dimethylphenylsilane as an end-capping marker group. The three stereoregular polymers synthesized include a 9,9-dihydridofluorene (PSF1), a 9,9-dimethyl-9H-fluorene (PSF2), and a 9,9′-spirobifluorene (PSF3) comonomer with the frameworks. These fluorenyl units are conjugated through the silicon center of the silafluorene moiety by bridging vinylene groups. Quantum yields of fluorescence range from 20 to 100% with PSF3 having the highest quantum efficiency. Polymers PSF1-3 emit in the blue region of the spectrum (∼475 nm), showing good color purity with little change in luminescence properties between the solution and solid-state phases. The polymers were tested for explosives detection properties by a fluorescence-quenching mechanism. Targeted explosives include laboratory prepared TNT, DNT, picric acid, RDX, HMX, PETN, TNG, and Tetryl, as well as production line PETN and C-4. All three polymers exhibit detection of explosive particulates with limits as low as 1 pg cm−2 for Tetryl. Polymer PSF1 simultaneously acts as a selective fluorescence “turn-on” sensor for nitrate ester explosives when irradiated with UV light. In the presence of nitrate ester-based explosives such as PETN, PSF1 initially exhibits fluorescence quenching, but continued exposure to UV-light (302 nm), promotes a photochemical reaction forming a luminescent green fluorenone copolymer. This is the first example of a single material acting as both a turn-off and turn-on selective fluorescent sensor for an explosive material.

Efficient blue-emitting silafluorene–fluorene-conjugated copolymers: selective turn-off/turn-on detection of explosives

The syntheses, spectroscopic characterization, and fluorescence quenching efficiencies of 1,1-silole− and 1,1-silafluorene−phenylenedivinylene polymers are reported. Model dimeric metallole compounds containing a phenylenedivinylene bridge have been synthesized to provide detailed structural and spectroscopic insight into conformational effects and electron delocalization. Poly((tetraphenyl)silole−phenylenedivinylene) and poly(silafluorene−phenylenedivinylene) both maintain a regioregular trans-vinylene Si−C backbone with σ*−π/π* conjugation. Various hydrosilylation catalysts were screened to evaluate their ability to produce high molecular weight polymers and to direct a strictly trans product. Molecular weights (Mw) for these polymers are in the range of 8400−9600. Fluorescence spectroscopy shows a significant bathochromic shift for the silafluorene polymer from solution to the solid state. A surface detection method for the analysis of solid particulates of TNT, DNT, PA, RDX, HMX, Tetryl, TNG, and PETN...

Catalytic Hydrosilylation Routes to Divinylbenzene Bridged Silole and Silafluorene Polymers. Applications to Surface Imaging of Explosive Particulates

The double transesterification polymerization of 3′,6′-bis(pinacolatoboron)fluoran and pentaerythritol is reported. A model dimeric compound was synthesized to demonstrate the effectiveness of bis-diols to undergo a double transesterification, which is driven by formation of the energetically favored six-membered di-ester ring from a monomer containing a five-membered di-ester ring. This synthetic procedure provides a new route to boronate based polymers, avoiding unstable boronic acid monomers. Formation of poly-3′,6′-bis(1,3,2-dioxaborinane)fluoran, with a molecular weight of 10 000, is complete after 48 h at 50 °C. The thermodynamic stability of the six-membered boronic ester rings present in the polymer backbone also improves the stability of the polymer and its resistance to oxidation under ambient and UV light conditions. A surface detection method for the analysis of H2O2 vapor by a fluorescence turn-on response was explored. The fluorescent response results from oxidative deprotection of the boronate functionalities forming green luminescent fluorescein. Detection limits as low as 3 ppb were observed for H2O2 over an 8 h period. Detection of H2O2 in liquids can also be carried out through spot tests at concentrations as low as 1 ppm after 5 min. This new vapor-phase sensor for H2O2 provides a robust, low-cost alternative to current technology for potential applications as a self-integrating sensor for the detection of H2O2 as well as the direct monitoring of H2O2 levels in areas such as cargo shipments, chemical facilities, and pulp bleaching.

/pdf/polymerization-of-a-boronate-functionalized-fluorophore-by-2smza679zq.pdf

Polymerization of a boronate-functionalized fluorophore by double transesterification: applications to fluorescence detection of hydrogen peroxide vapor

Polycarbosilanes exhibit desirable physiochemical properties such as high thermal stability, elastomeric behavior, diverse functional group tolerance, electronic delocalization, and ease of synthesis. New ceramic precursors, fire-retardant materials, and flexible conducting polymers have been created using polycarbosilanes. Catalytic hydrosilylation provides a convenient synthetic route to these materials. With its tolerance of many functional groups, catalytic hydrosilylation offers one-step syntheses of both aliphatic and olefinic polymers and dendrimers whose electronic properties can be tuned selectively. Copolymerization of conjugated diynes with compounds that contain the silole chromophore offers a route to new luminescent materials that have been applied to the detection of explosives and may be promising organic light-emitting diode materials. An important feature of the silole materials is the Lewis acidity at silicon, which offers a function not often present in organic polymers.

Jason C. Sanchez

Papers

Synthesis, Luminescence Properties, and Explosives Sensing with 1,1-Tetraphenylsilole- and 1,1-Silafluorene-vinylene Polymers

Efficient blue-emitting silafluorene–fluorene-conjugated copolymers: selective turn-off/turn-on detection of explosives

Catalytic Hydrosilylation Routes to Divinylbenzene Bridged Silole and Silafluorene Polymers. Applications to Surface Imaging of Explosive Particulates

Polymerization of a boronate-functionalized fluorophore by double transesterification: applications to fluorescence detection of hydrogen peroxide vapor

Hydrosilylation of Diynes as a Route to Functional Polymers Delocalized Through Silicon