Aggregation Induced Emission of 9,10 ... - ACS Publications

Chapter 7

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Aggregation Induced Emission of 9,10-Distrylanthracene Derivatives: Molecular Design and Applications Bin Xu and Wenjing Tian* State Key Laboratory of Supramolecular Structure and Materials, Jilin University, Changchun 130012, P. R. China *E-mail: [email protected]

The development of efficient luminescent materials in the solid state is of great interest for their potential applications. An inevitable obstacle of their development is the notorious aggregation-caused quenching (ACQ), i.e., the emission is often quenched in the solid state. Since Tang et al. first demonstrated the unique phenomenon of aggregation induced emission (AIE) in 2001, molecules with such properties started to draw more and more attentions. Among the AIE molecules, 9,10-distyrylanthrance (DSA) and its derivatives become very important luminogens, which possessing typical AIE behavior: weaken emission in solution, whereas boost and enhance emission in aggregate state. The restricted intramolecular rotation was demonstrated to be the origin of AIE properties in DSA derivatives. Herein we present the current aspects of the AIE properties of DSA and its derivatives, paying particular attention to the molecule system and their applications in solid state emitter, stimuli-responses, fluorescent sensors and bioimaging.

© 2016 American Chemical Society Fujiki et al.; Aggregation-Induced Emission: Materials and Applications Volume 1 ACS Symposium Series; American Chemical Society: Washington, DC, 2016.


Introduction Luminescent materials have been attracted intensive interests due to their wide applications in fundamental and technological field. Luminescence is an emission of ultraviolet, visible or infrared photon from an electronically excited species. Luminescence is cold light, to describe ‘all those phenomena of light which are not solely conditioned by the rise in temperature’, and formally divided into fluorescence and phosphorescence depending on the nature of the excited state. However, most organic luminescent materials have strong emission and high quantum yield in solution, but the quantum yield of them generally decreases in the solid state. The aggregation caused quenching (ACQ) effect has limited the scope of technological applications of the luminescent materials (1, 2). To mitigate the ACQ effect, various chemical, physical and engineering approaches have been developed. For example, branched chains, bulky cyclics, spiro kinks and dendritic wedges have been attached to aromatic rings to obstruct the formation of aggregates. Another approach is the spatial distribution of the fluorophore dopants in a doped film, which is usual a non-conjugated transparent polymer poly(methyl methacrylate). Although various approaches have been taken into interface with luminogens, the aggregation of luminogens still occurs in many cases (3, 4). In 2001, Tang and co-workers were attracted by a group of organic molecules called siloles (named hexaphenylsilole), which were found to be virtually non-luminescent when molecularly dissolved in good solvents, but became strong emissive when aggregated in poor solvents or fabricated into thin solid films. They coined the term “aggregation-induced emission” (AIE) for this intriguing phenomenon (5, 6), because the non-luminescent silole molecules were induced to emit by aggregation. Unlike ACQ materials that perform better as isolated species, AIE luminogens perfectly embody the philosophical idea of Aesop: “United we stand, divided we fall!” Attracted by the fascinating feature, many groups all over the world have worked on the design and synthesis of new AIE luminogens, preparation and modulation of their aggregate morphologies, investigation and manipulation of their luminescence behaviors, and development of their applications. As a result of the research efforts, a variety of novel AIE molecule systems have been developed, and a number of practical applications have been explored. The intension of this chapter is to emphasize the current aspects of the AIE properties of 9,10-distyrylanthracene (DSA) derivatives, paying particular attention to the molecule system and their applications. Any discussion of other AIE molecule system besides DSA derivatives is outside the scope of this chapter and will be dealt with in other chapters of this ACS e-book.

The AIE Luminogens Based on 9,10-Distyrylanthracene Since the pioneering research on the AIE phenomenon of silole derivatives in 2001, a large variety of AIE molecules have been developedwith great structural diversity (5–7). And among them, the DSA derivatives are of great interest for the concise structures, intriguing performance and the wide range of applications. 114 Fujiki et al.; Aggregation-Induced Emission: Materials and Applications Volume 1 ACS Symposium Series; American Chemical Society: Washington, DC, 2016.


As the basic building block of the varying derivatives, DSA can be easily prepared by Heck reaction from styrene and 9,10-dibromoanthracene catalyzed by K3PO4 and Pd(OAc)2 in dry dimethylacetamide, and the derivatives can be synthesized in similar procedures. Besides, Witting-Horner reaction is also capable of introducing the trans-vinyl. Based on these reactions, the AIE systems containing with DSA are gradually enlarged, including small molecules and macromolecules. Although the origins of these enhanced emissions of DSA system are still in debate, it is assumed that the unique fluorescence phenomenon is related to the effects of intramolecular planarization, the formation of specific aggregation, and blockage of non-radiative relaxation pathways of the excited species. The restricted intramolecular rotation (RIR) process has been proposed to be the main cause for most of the reported AIE molecule systems (8, 9). Under the experimental and theoretical analysis, the fluorescence of DSA-based molecules is affected not only by non-radiative processes, but also by the radiative processes. Thus both the molecular conformation and intermolecular interactions should be taken into account. For crystalline small molecules, the packing structures of crystals provide an insight view to see how the molecules perform when they aggregate. Various supramolecular interactions such as CH-π interaction and hydrogen bond are found to construct the crystals (10–12), and the molecular conformation is significantly distorted, suggesting that the free intramolecular rotation in solutions is easier to happen than in aggregates. The RIR will operate and boost the emission in the aggregate state. However, for macromolecules such as oligomers, dendrimers and polymers, the intramolecular rotation is also responsible for the extremely low quantum efficiency. Besides, the introduction of groups with specific properties, such as electron donating and withdrawing units, may construct a charge transfer structure. Thus the excited molecules may form twisted intermolecular charge transfer state (TICT) in polar solvents, which is also infaust for emission, accompanied by free intramolecular rotational motions in solution (13). Though inferred from single crystal, the conclusion above is also applicable for those aggregates which are more amorphous than crystalline. The intrinsic steric hindrance provided by 9,10-divinylanthracene (DVA) moiety plays a crucial role in overcoming the fluorescence quenching in aggregates, both for small molecules and macromolecules. The parallel face-to-face intermolecular interactions in the aggregated state can be avoided by virtue of the twisted DVA groups (14, 15). By analyzing the absorption spectra of the aggregates, one can easily figure out whether the cofacial aggregation is formed or not. Usually, a hypochromatic shift in absorption compared with that of isolated state means the formation of cofacial configuration according to quantum-chemical calculations (13).

115 Fujiki et al.; Aggregation-Induced Emission: Materials and Applications Volume 1 ACS Symposium Series; American Chemical Society: Washington, DC, 2016.


Scheme 1. The synthetic routes and molecular structures of small molecules based on DSA.

Small Molecules The synthesis of DSA derivatives were first reported by Fabin et al. in 1991 (16), yet few attentions had been paid to their fluorescence behavior. The discovery of AIE in 2001 encouraged us to develop efficient luminescent materials for practical applications. As a kind of π-conjugated organic molecule, anthracene was reported by Prasad et al. in 2006 that the emission of 9,10-bis[4′-(4′′-aminostyryl)styryl]anthracene (BDSA) (Figure 8) in nanoaggregates (17) enhanced sharply, but few AIE-active molecules with anthrylene core have been developed, until Tian and Xu et. al. demonstrated the structures and properties of a serial of DSA derivatives (1, 3, 4) (10). The derivatives of DSA (1-9), whose molecular structure were shown in Scheme 1, exhibit typical AIE properties, both in nanoaggregates and crystals. The distorted conformation prevents the face to face stacking and the restricted intramolecular rotation blocks the non-radiative pathway greatly. 2 with methyl was presented in the following research, where the methyl was added intentionally to control the molecular packing (11). 116 Fujiki et al.; Aggregation-Induced Emission: Materials and Applications Volume 1 ACS Symposium Series; American Chemical Society: Washington, DC, 2016.


To further investigate the relation between the structures and properties of DSA-based molecules, we designed and synthesized three derivatives substituted at meta-position (10-12) (12). And proper chemical modification leads to various applications of DSA derivatives utilizing the intrinsic property of the high quantum yield in aggregates state (8-9), such as the fluorescence probes (18). In addition, the DSA derivatives used for two photon technique are of great importance for their potential applications for bioimaging, photodynamic therapy and so on. The DSA derivative (BDSA) with a highly extended π-conjugation and the appropriate intramolecular charge transfer was developed (11, 19). When indroduce the pyridine group into DSA structure, one representative example is 13, which possessing three polymorphs in crystals and exhibiting gradually red-shifted emission upon applied pressure (19). Besides, DSA derivatives containing other substituent site of pyridine (14, 15) are also piezochromic materials, perhaps due to the relatively loose packing in aggregates (20).

Macromolecules Much progress has been reported regarding small molecular AIE luminogens, but some macromolecules containing 9,10-divinylanthracene segments also show fascinating AIE properties and assume good candidates for various application (21). The DSA-based oligocarbazoles 16 show a self-assembling properties and an amazing emission behavior (14), which draw a great interesting to see how the aggregate structures will be affected by the molecular structure. On the other hand, AIE polymers based on DSA have been rarely reported (Scheme 2, 17-26). Recently, a serial of copolymers containing AIE moieties were presented for bioimaging. And following studies reveals that fluorine-containing segments are of great importance to further improve the performance. Besides, the integration of 19F segments makes the polymers suitable for 19F magnetic resonance imaging (22, 23). Two AIE-conjugated block copolymer containing an AIE fluorophore, 9,10-bis(4-hydroxystyryl)anthracene, hydrophobic poly(3-caprolactone) segments, hydrophilic poly(ethyleneglycol) segments and folate groups (Scheme 2, 27, 28) were developed, which can form the fluorescence polymer dots (Pdots) by self-assembly procedure and achieve the specific cellular imaging. Dendrimers based on DSA with the introduction of triphenylamine branchs (29-31) were developed. These dendrimers not only exhibited the typical AIE feature, but alos poessess large triphenylamine (TPA) cross section accompanied by the high quantum yield (15).



Scheme 2. The molecular structures of macromolecules based on DSA.


Applications of AIE Luminogens Based on 9,10Distyrylanthracene


New concept and relevant research will lead to new applications. The AIE luminogens are highly emissive in aggregate state, providing a wide range of applications. AIE luminogens can serve as efficient solid state emitters for their high quantum yields, also the emission properties can be switched upon external stimuli. Additionally, many efforts have been devoted to their utilities in fluorescent sensors and bioimaging.

Solid State Emitter Owing to the excellent luminescence in aggregate state, DSA derivatives are promising solid state emitters, such as crystals, films and nanomaterials. Related research has begun since a serial of DSA derivatives was reported by our group in 2009 (10). Molecules based on 9,10-distyrylanthracene (1, 5) were synthesized, and single crystals were prepared. Tight intermolecular stacking via supramolecular interactions conducts the formation of high quality needle-like single crystals. These molecules possess typical AIE behavior. The quantum yield of DSA in nanoaggregates state is 50%, which is nearly 125 times larger than that of solution. The relationship between the crystal structures and AIE properties of these molecules indicates that the DSA moiety is the key factor of the AIE property due to the restricted intramolecular torsion between the 9,10-anthylene core and the vinylene segment. Owing to high solid state fluorescence efficiency, this kind of single crystals show a great potential application for organic solid state laser. Single crystals based on 9,10-bis(2,2-diphenylvinyl)anthracene (BDPVA) (24), 9,10-bis(2,2-dip-tolylvinyl)anthracene (BDTVA) (25), and methyl-substituted 9,10-distyrylanthracene 2 (11) were investigated by characterizing the amplified spontaneous emission (ASE) properties. Large needle like crystals were formed by CH/π interactions. Relatively large torsion angles between the anthracene center and the vinylene moieties substituted prevent the interaction between adjacent molecules. (Figure 1) Notablly, the molecular packing in BDPVA crystal is cross-dipole stacking, which is rarely reported and predicted to be beneficial to the light emitting (26).



Figure 1. a) Single crystal of BDPVA under UV light (365 nm). b) Two conformational structures of BDPVA in the crystal. c) Stacking of molecular columns and d) the cross stacking molecules in one column (view along b axis). Hydrogen atoms are omitted for clarity. Conformation A1 is drawn in blue and A2 in red. d = 5.645 Å. e) UV–vis and PL spectra of BDPVA in tetrahydrofuran (THF) and crystals. f) PL spectra of a BDPVA crystal as the function of the pump laser energy. Reprinted with permission from ref. (25), Copyright 2015 American Chemical Society. High quality crystals with regular structure ensure the wave-guided propagation of emission for ASE and lasing. When pumped by a pulse laser, the these crystals all show typical gain-narrowed spectra due to stimulated emission. Unlike the broad and weak emission under weak incident intensities that corresponds to spontaneous emission, the full width at half maximum (FWHM) drops dramatically with the intensity of emission growing rapidly upon increasing pump energy. The ASE thresholds for BDPVA, BDTVA, and 2 are determined to be 21 kW cm-2, 27 kW cm-2, and 170 kW cm-2, respectively, indicating that the crystals are good candidates for organic solid-state laser. The terminal substituent group on the molecules can greatly influence the optical properties. Cyan-substituted 6 and tertiary butyl- substituted 7 DSA derivatives can arrange in the same conformation and orientation in their crystals, which is called uniaxially oriented packing. Introducing halogen atoms to the structures can also influence the photophysical properties of 9,10-distyrylanthracene. DSA derivatives with fluorine, chlorine, bromine, and 120 Fujiki et al.; Aggregation-Induced Emission: Materials and Applications Volume 1 ACS Symposium Series; American Chemical Society: Washington, DC, 2016.


iodine were successfully synthesized (27). In these materials on crystalline state, the emission red shift from 515 nm to 554 nm with the increasing of the atomic number of the terminal substituent. These studies based on substituent modification can help researchers acquire a good understand on the role of the substituent in tuning the photophysical properties of DSA and develop other DSA materials.

Figure 2. Illustration of ordered one-dimensional (1D) nanostructures based on DSA derivatives. Reprinted with permission from ref. (12), Copyright 2012 Royal Society of Chemistry. Besides single crystals, ordered one-dimensional (1D) nanostructures based on DSA have also been reported (10-12) (12). Intense emission (ΦF 75% for 11 and 73% for 12) in crystals and self-assembly properties were investigated. Compared to the formation of luminescent rodlike microcrystals from 1 and 10, F substituent is thought to play a key role in the self-assembly process.(Figure 2) Introducing F substituent in DSA leads to strong intermolecular CH…F interactions, meanwhile induce intermolecular π-π stacking. Further investigation reveals that varying fabrication methods bring about different structures of nanowires, 1D nanowires can be easily prepared by a reprecipitation approach in CHCl3, while much larger rodlike microcrystals are obtained by physical vapor deposition. Such highly efficient crystalline 1D nanowires are potential candidates in applications such as nanoscale optoelectronics, sensing and biological devices. Interestingly, oligocarbazole derivatives 16 (n=2) containing 9,10divinylanthracene segment can form regular nanorings rather than particles from other two oligomer. The nanoring possesses a discrete shape with outer and inner diameters around 200 nm and 130 nm, showing strong green emission (ΦF=30%) upon photoexcitation, which may serve as a promising building block for miniature electronic and photonic devices. 121 Fujiki et al.; Aggregation-Induced Emission: Materials and Applications Volume 1 ACS Symposium Series; American Chemical Society: Washington, DC, 2016.


In addition to the applications for linear optics severd as emitters, DSA derivatives have also been utilized for nonlinear optics such as two-photon fluorescence materials. The DSA-based dendrimers (29-31) with high TPA cross section are developed (28). The maximum values of the two-photon absorption cross section are 407 GM for 29, 1850 GM for 30 and 5180 GM for 31, and the broad bandof large TPA cross section permits a lot of flexibility in terms of the excitation wavelength that can be used in two–photon applications. Besides the materials, the idea of developing TPA molecules with high TPA cross section and fluorescence quantum yield in the aggregate state by using a valid dendritic strategy is significative.

Stimuli-Responses Stimuli-responsive luminescence materials, as a kind of smart materials, are attracting considerable attention because of their potential applications in sensors, optoelectronic devices and data storage. A part of DSA derivatives not only show AIE property but also exhibit fascinating mechanochromism, thermochromism, acidichromism and so on. Herein, we attempt to highlight the most significant developments in stimuli responsive luminescence-changing materials based on the DSA derivatives and provide an overall understanding of the underlying origin of stimuli-responsive luminescence changing. The first example of DSA derivatives with piezochromism behavior is 9,10bis((E)-2-(pyridin- 2-yl)vinyl)anthracene 13, which is also AIE active (29). 13 exhibited unusual spectacular luminescence characteristics: grinding and exertion of external pressure on the powder led to a change in its photoluminescence color from green to red. The initial 13 powder exhibited a strong green emission which peaked at 528 nm. After grinding, 13 powder showed a large red shift with a yellow emission (λem = 561 nm), and after being heated above 160 °C, the ground powder recovered to its initial green emission (λem= 528 nm). The two emission colors are completely reversible through grinding and heating, indicating that the 13 powder possess a significant piezochromic effect. To further understand the pizeochromic behavior, we firstly reported the luminescence behavior of luminogen under applied pressure. As the applied pressure increased, the emission of the 13 powder clearly showed a gradual red shift. It shows that the applied pressure from 0 - 8 GPa caused a more noticeable luminescent color change of 13 powder from green (528 nm) to red (652 nm) than that upon grinding, which is the largest shift in piezochromic effect ever reported at present. This suggests apparently that the grinding method is not enough to cause a stronger piezochromic effect in the case of 13. Single crystals analysis can provide a powerful tool to understand the relationship between molecular aggregation state and luminescence properties directly and definitely. Fortunately, three crystal polymorphs of 13 with different luminiescence and stacking modes can be obtained. These crystals show different luminiescence peaked at 527 nm (C1), 579 nm (C2) and 618 nm (C3), respectively, and involve gradually enhanced π-π interactions in the three crystalline states, as shown in Figure 3. In the case of C1, molecules adopt a stack mode of J-type 122 Fujiki et al.; Aggregation-Induced Emission: Materials and Applications Volume 1 ACS Symposium Series; American Chemical Society: Washington, DC, 2016.


aggregation along the Y axis. While in C2, H-type aggregation is formed along the X axis. In particular, dimers with tight face-to-face stack are found in C3 along the X axis. It is worth noting that the overlap of anthracene planes between the adjacent molecules is increased from C1 to C3. These different stack modes in C1, C2 and C3, reasonably result in various molecular aggregation state, leading to diverse the fluorescence colors, which obviously indicates that 13 possesses three or even more different aggregation structures in solid state. Such a strong π-π interaction induced the red emission of C3 with λmax at 618 nm to show a redshift relative to those of C1 and C2. These redshifts thus can be resulted from the reduced band gap of 13 molecule owing to the enhanced π-π interaction in terms of tight-binding model, which suppose that the band gap depends on the degree of π-π interaction of chromophores. Nonetheless, another important factor for the red shifted fluorescence should be taken into consideration, that is, the increase of exciton coupling and orbital overlap between neighboring molecules from C1 over C2 to C3, which could lead to a strong red shift of the emission of the lowest state of the coupled chromophores. Therefore, these suggested that the PL emission of 13 in aggregation/solid state could be changed by altering its molecular stacking mode.

Figure 3. Stacking modes and corresponding emission colors for the various molecular aggregation states in 13 powder. Reprinted with permission from ref. (29), Copyright 2012 Wiley-VCH. The intramolecular effect is another important factor which will effectively influence the absorption and emission spectra of the compounds under mechanical force stimuli. Many AIE molecules possess pizeochromic behavior, which is often ascribed to the better coplanarity than the initial twisted conformation under pressure or grinding. For example, an anthracene derivative (TPE-An) containing tetraphenylethylene moieties (Figure 4) exhibits obvious mechanochromic and AIE properties (30). After grinding, the emission wavelength increased from 506 nm to 574 nm. The WAXD results indicated that the mechanofluorochromic resulted from the reversible morphological change between the crystalline and amorphous structures. TPE-An molecule adopts a highly twisted conformation due to the existed steric hindrance between the aryl rings. 123 Fujiki et al.; Aggregation-Induced Emission: Materials and Applications Volume 1 ACS Symposium Series; American Chemical Society: Washington, DC, 2016.


Figure 4. a) Molecular structure of TPE-An and b) PL spectra of TPE-An in water/THF mixtures. c) The images of TPE-An taken at room temperature under stimuli and the WAXD pattern together with the normalized PL spectra. Reprinted with permission from ref. (30), Copyright 2011 Wiley-VCH.

Figure 5. The emission switch of 15 powder under different stimuli, and the frontier molecular orbitals based on the protonation–deprotonation of the pyridine moieties in 15 and the redshifted emission under different hydrostatic pressure. Reprinted with permission from ref. (32), Copyright 2013 The Royal Society of Chemistry. 124 Fujiki et al.; Aggregation-Induced Emission: Materials and Applications Volume 1 ACS Symposium Series; American Chemical Society: Washington, DC, 2016.


Another important stimuli-responsive luminescence is acidichromism. A remarkable fluorescence changing behavior of 9,10-bis((E)-2-(pyridin-3yl)vinyl)anthracene 14 based on the protonation–deprotonation process in the aggregate state is observed, including single crystals and powders (31). The powders of 14 exhibit a strong green emission at 525 nm. Additionally, fumigation of hydrochloride (HCl) vapor has significant effects on the fluorescence of the 14 powder, turning it from green (λem = 525 nm) to orange (λem = 586 nm), and the deprotonation with the aid of triethylamine (TEA) vapor can lead to a partially recovered to initial green emission (λem = 534 nm). Then we turn to crystals to study the origin of the fluorescence changes. Large single crystals of 14 and protonated 14 (14-HCl) with totally different emission colors were obtained by using the solvent evaporation approach. The study on the 14 and 14-HCl single crystals will provide a new insights into the mechanism of such stimuli-response luminescent materials. The emission peaks of the two crystals are located and 528 nm and 590 nm, with quantum efficiencies of 0.44 and 0.40, respectively. The analysis of single crystals reveals the definite protonation process in 14, which results in 60 nm shift in fluorescence changing, from green to orange. With the X-ray structural analysis and theoretical calculation, reveal that the fluorescence change originates from two aspects, one is the intermolecular enhanced excitonic coupling and the other is the enhanced electron delocalization through intramolecular charge transfer (ICT) effect. More interesting, another DSA derivative, 9,10-bis((E)-2-(pyridin-4yl)vinyl)anthracene 15 exhibits multi-stimuli responsive fluorescence changes under pressure, heat, acid and base stimuli as shown in Figure 5 (32). The emission of 15 powders can be changed from green to yellow upon grinding. The obtained two polymorph crystals with different emission color make a bridge for building the relationship between the packing pattern and emission color. 15 molecules in C1 possess a stacking structure with J-aggregation while the ones in C2 are the H-aggregation mode with 40% overlap of the anthracene plane. Therefore, we can infer the change of fluorescence under external pressure may originate from the transformation of the stacking structures. Additionally, protonation–deprotonation of the pyridine moieties in 15 has a significant effect on the frontier molecular orbitals, resulting in distinct green and red emissions under acid and base stimuli. By the quantum chemical calculation, the protonation of pyridine enhance the electron-withdrawing ability, resulting in the delocalization of π electrons and the decreased bandgap. These provide a comprehensive insight into the mechanisms within this type of mutlti stimuli-responsive luminescent material. And it also suggests that 15 may be a potential candidate for applications in sensing, detection and display devices with remarkable color-changing properties.

Fluorescent Probes and Sensing Fluorescent probes are the most promising tools for analytical sensing, which allow direct visualization of biological analytes at the molecular level, and have potential applications in chemistry, materials science, biology, and medicine. The 125 Fujiki et al.; Aggregation-Induced Emission: Materials and Applications Volume 1 ACS Symposium Series; American Chemical Society: Washington, DC, 2016.


fluorescence-based sensing technique offers excellent selectivity, high sensitivity and wide dynamic ranges. However, the ACQ effect seriously restricts the development of efficient fluorescence sensing and often result a “turn-off” mode in fluorescence signal. The unique AIE phenomenon offers a straightforward solution to the ACQ problem, and a large number of AIE-active probes have been used for fluorescence turn-on sensing. Moreover, the advantages of these sensors are obvious, (1) the problem of ACQ is avoided and hence the effective ranges of the sensors are extended, and (2) the fluorescence is turned on from a dark state making the detection more sensitive and faster, and (3) AIE-active sensors based on a new mechanism instead of those conventional sensors are utilizing, for instance, fluorescence resonance energy transfer (FRET), thus some new possibilities for species detection are offered.

Figure 6. Schematic illustration of Pb2+ sensing mechanism. a) Fluorescence spectra of P1 in the presence of different concentrations of Pb2+. Experimental conditions: 5.0 mM P1, 5.0 mM TBA, 11U nuclease S1 (2 min) in 20 mM Tris –HAc, pH= 7.2 buffer solution. (b) Plot of /562 at the concentration of Pb2+. Inset: expanded low-Pb2+concentration region of the calibration curve. Reprinted with permission from ref. (34), Copyright 2013 The Royal Society of Chemistry. 126 Fujiki et al.; Aggregation-Induced Emission: Materials and Applications Volume 1 ACS Symposium Series; American Chemical Society: Washington, DC, 2016.


Various AIE luminogens have been utilized as sensitive, selective and turn-on chemosensors and bioprobes. On the basis of DSA derivatives, various chemosensors for specific chemical substances detection including ion and organic molecules have been widely developed. Based on a AIE-active 9,10-distyrylanthracene as a fluorophore and thymine as a Hg2+ receptor (33), a DSA molecule 9,10-bis(4-2-(thymineethoxy) styryl) anthracene (DSA-T2) has been successfully synthesized as a fluorescence indicator for specific Hg2+ detection via a thymine-Hg2+-thymine complex. The limitation of detection (LOD) of Hg2+ can reach as low as 3.4×10-7 mol L-1, given its easy operation, good sensitivity and good selectivity, this probe shows great promise for environmental monitoring. The quaternary ammonium salt of DSA with two side arms, used as a fluorescent probe (Figure 6, compound P1), is studied for label-free and turn-on fluorescence detection of Pb2+ through Pb2+-induced allosteric G4 of a thrombin binding aptamer (TBA, GGTTGGTGTGGTTGG) (34). In the presence of Pb2+, TBA folds into a stable G4 structure which blocks hydrolysis digestion of nuclease S1, DSA molecule aggregates on the stable G4 structure due to the electrostatic interactions between ammonium cations of probe and the backbone negative phosphate anions of G4 and the possible hydrophobic interaction between nucleosides and aryl rings in probe, leading to a favorable turn-on mode in fluorescence emission. In the absence of Pb2+, however, nuclease S1 efficiently degrades ssDNA into mono- or oligonucleotide fragments, on addition of probe, TBA fragments cannot induce aggregation formation of the probes and so result in weak fluorescence intensity. Moreover, only fluorescence enhancement in the presence of Pb2+ indicates excellent sensing selectivity of Pb2+, and the fluorescence intensity is directly proportional to the amount of Pb2+ added, a linear range is observed from 0 to 0.6 mM and from 0.6 mM to 200 mM Pb2+. The detection limit of the present approach can reach to 60 nM with a signal-to-noise ratio of 3. Compound P1 not only uses in Pb2+ detection, but has also been used to construct a novel biosensor for real-time sensing of nuclease activity and inhibition.[35] In the absence of S1 nuclease, the fluorescence remains constant over the period. However, the FL intensity obviously decreases with the increase of S1 nuclease concentration over the range of 6-32 U ml−1. This indicates that ssDNA is the substrate for S1 nuclease and could be effectively cleaved by S1 nuclease, and the DNA fragmentation could not induce aggregation of compound P1, leading to decreasing in fluorescence emission. Na2ATP, the effective inhibitor, is used to prevent the cleavage of ssDNA with S1 nuclease. In the absence of Na2ATP, the fluorescent intensity of the complex obviously decreased with increasing reaction time, indicating that the cleavage reaction proceeded well. While in the presence of different concentrations of Na2ATP, the extent of fluorescent recovery increases gradually with increasing Na2ATP, implying that the cleavage reaction by S1 nuclease is prohibited, and the digestion of ssDNA by S1 nuclease is effectively inhibited by Na2ATP at the concentration of 0.4 mM. As a novel fluorescent biosensor, probe/ssDNA complex can be used not only for label-free fluorescent nuclease activity sensing but also for turn-on assay of nuclease inhibitors in real time. 127 Fujiki et al.; Aggregation-Induced Emission: Materials and Applications Volume 1 ACS Symposium Series; American Chemical Society: Washington, DC, 2016.


Figure 7. Schematic Description of Selective Fluorescent Aptasensor Based on 9/GO Probe. reprinted with permission from ref. (37), Copyright 2014 The Royal Society of Chemistry. Another DSA derivative, 4,4′-(1E,1′E)-2,2′-(anthracene-9,10-diyl)bis (ethene-2,1-diyl)bis(N,N,N-trimethyl-benzenaminium)iodide (9), used as a label free and turn-on fluorescent probe, is developed for specific Ag+ sensing (36). Here the cytosine-rich ssDNA (oligo-C) is chosen because it could be induced to form a hairpin structure in the presence of Ag+ via the C-Ag+-C base pair. Nuclease S1 is used to improve the sensitivity of Ag+ detection due to its effecient hydrolyzation ability towards ssDNA. In the solution of oligo-C, Ag+ and 9, oligo-C forms a hairpin structure via the C-Ag+-C base pair and 9 aggregates on the surface of the hairpin structure to produce a strong emission, while in the absence of Ag+, oligo-C can not form a stable hairpin structure, then it is broken into fragments by nuclease S1, this means 9 can not aggregate, leading to non-emission of the solution. The detection limit is estimated to be 155 nmol L−1. A label-free and turn on fluorescence biosensor as shown in Figure 7 is fabricated for selective and sensitive sensing of targeted DNA and thrombin protein by using 4,4′-(1E,1′E)-2,2′-(anthracene-9,10-diyl)bis(ethene-2,1-diyl) bis(N,N,N-trimethylben zenaminium)iodide (9) as a fluorescence indicator together with graphene oxide (GO) as a fluorescence quencher (37). 9 is weak emissive in tris-HAc solution, upon addition of single-stranded (ss) DNA aptamer, it becomes strong emissive due to the formation of 9-ssDNA aptamer complex via the electrostatic interactions and the hydrophobic interaction. When the GO is added, the adsorptive binding of ssDNA aptamer to GO guarantees the close proximity of 9/ssDNA aptamer complex to GO, and the following FRET from 9 to GO should occur, leading to dramatically fluorescence quenching. Only when the targeted complementary ssDNA is added into the aptamer solution, the binding between the ssDNA and the targeted ssDNA will alter the conformation of ssDNA aptamer and form dsDNA, which reduces the π−π stacking and hydrogen 128 Fujiki et al.; Aggregation-Induced Emission: Materials and Applications Volume 1 ACS Symposium Series; American Chemical Society: Washington, DC, 2016.

bonding interaction between GO and aptamers. Meanwhile, 9 still adsorbs on the established dsDNA and stays away from GO, and the fluorescence of 9/dsDNA complex will be recovered and enhanced gradually. Similar phenomenon is observed in 9/GO-based aptasensor for protein detection, the specific binding interaction of DNA aptamer and protein allows selective sensing for both DNA and protein.


Bioimaging Fluorescence-based optical imaging is of vital importance for biological investigation, such as metabolism and pharmacokinetics. The advantages of AIE luminogens are more evident. AIE-active sensors have been widely explored for the detection of DNA, heparin, and ATP, but fewer studies were reported about the applications of the AIE fluorophores as bioimaging probes, perhaps for the hydrophobic nature of the dyes. Up to now, there are three types of fluorescent nanoparticles based on DSA fluorogens. The first part covers the most widely studied physical cladding DSA fluorogens fluorescent nanoparticles, in which the DSA fluorogens are encapsulated into the polymer matrix. The second part is focused on the covalent AIE fluorogens copolymer fluorescent nanoparticles. The last part shows the recent development of fluorescnet silica nanoparticles based on DSA fluorogens, such as encapsulated DSA fluorogens silica nanoparticles and covalent binding DSA fluorogens silica nanoparticles. An18-F127 fluorescent organic nanoparticles were obtained by combine AIEbased luminogens An18 (derivatized from 9,10-distyrylanthracene with an alkoxyl endgroup) and surfactant Pluronic F127 (38). The An18–F127 composite emitted strong fluorescence in water with significantly enhanced FL intensity compared with that of luminogens An18 in THF solution. The bright yellow fluorescence were observed when A549 cells were incubated with 40 μg/mL of An18–F127 for 3 h by using confocal laser scanning microscopy (CLSM). An AIE luminogens (2-(2,6-bis((E)-2-(5-(N,N- bis(4-((E)-2-(10-((E)-4(diphenylamino)styryl)anthracen-9-yl)vinyl)phenyl)aniline-4-yl)thiophen-2yl)vinyl)-4H-pyran-4-ylidene)malononitrile) 32 with near-infrared emission was developed by coating disc-like red emission fluorophores with propeller-shaped AIE fluorophores (39). The ultrabright red AIE dots 32@Ps-PVPs were fabricated by using the AIE molecule 32 as the core and one biocompatible polymer Ps-PVP as the encapsulation matrix. The best fluorescence quantum yield of 12.9% can be achieved. The morphology from the TEM indicates that the prepared AIE dots are well shaped nanospheres with an almost uniform size around 25 nm. Dynamic light scattering (DLS) studies of the dots confirmed the monodisperse and uniform size by showing a narrow peak. After incubation with the 32@Ps-PVPs suspension (0.15mg/mL) for 16 h at 37 °C in the culture medium, the HeLa cells were imaged by CLSM with a 405 nm laser excitation and the fluorescent signals were collected between 610 nm and 710 nm, and an intense red fluorescence was observed in the cellular cytoplasms and nuclei. 129 Fujiki et al.; Aggregation-Induced Emission: Materials and Applications Volume 1 ACS Symposium Series; American Chemical Society: Washington, DC, 2016.


Figure 8. a) A possible schematic drawing of the micelles formed from the polymers using a flower-micelle model. b) 19F NMR spectra of PF1 to PF4 in H2O and DMSO (98 : 2 by volume) at 10 mg/m; c) Schematic drawing of the preparation of AIE Pdots. d) Enlarged TEM image of Pdots. Reprinted with permission from ref. (40) &(42), Copyright 2012 & 2014 The Royal Society of Chemistry. Covalent AIE Copolymer is another importand way to fabricate high efficent fluorescenct nanoparticles. Random copolymers (17-21) based on N-(2-hydroxypropyl)methacrylamide (HPMA), 2-aminoethyl methacrylate (AEMA) and DSA luminogens are exploited (Figure 8), because HPMA moieties are biocompatible with little or non-cytotoxicity, and AEMA is used to enhance the cellular uptake of polymers (40). Five copolymers containing different fraction of AIE moieties are synthesized and all exhibit typical AIE properties in DMSO/H2O mixtures. At the same DMSO/H2O ratio, the polymers with more fractions of AIE segments have higher quantum efficiencies before the fraction reaches a certain level. The confocal fluorescence microscopy images of one typical polymer for two cell lines (U87MG and CP-A) after 24 hour internalization with cells at 37°C reveals that the polymer are successfully taken up by the cells and are randomly distributed in the cytoplasma area of the cells. Following cytotoxicity evaluation using MTT assay shows that the polymers do not show obvious cytotoxicity to the two experimental cell lines after cellular internalization for 24 hours with a polymer concentration up to 1 mg/ml. Based on the polymers above, a serial of novel polymers containing AIE fluorophores as well as fluorine segments were developed (22-26) (41). Furthermore, since 19F segments are the critical elements for 19F magnetic resonance imaging (MRI), the integration of 19F segments with AIE moieties extent the applications of the polymers not only for fluorescence bioimaging, but also for 19F MRI. 130 Fujiki et al.; Aggregation-Induced Emission: Materials and Applications Volume 1 ACS Symposium Series; American Chemical Society: Washington, DC, 2016.


All the polymers were taken up by two cell lines to study their application on bioimaging. The confocal fluorescence microscopy images revealed that the polymers were randomly distributed in the cytoplasm area, instead of specific localizations in the organelles like lysosomes and mitochondria. Cytotoxicity evaluation shows the less-toxic copolymers may have potentials for in vivo applications. In addition, the micelles derived from polymers 22-24 exhibited a single and narrow resonance on 19F MRI. With more fluorine-containing hydrophobic segments in the micellar cores, the motion of fluorine atoms was more restricted, resulting in the broad and weak signal of 25. Also the polymers showed reasonable T1 and T2 values. An AIE-conjugated block copolymer containing an AIE fluorophore, 9,10-bis(4-hydroxystyryl)anthracene, hydrophobic poly(3-caprolactone) segments, hydrophilic poly(ethyleneglycol) segments and folate groups were developed. In order to increase the ability of specific recognition to the block copolymer 27, folic acid (FA) was modified to the terminal 28 (42). Taking advantage of the amphiphilic properties from copolymers, AIE Pdots could be easily prepared when H2O was slowly dropped into the THF solution of the copolymers. The PCL segments and AIE fluorophore are encapsulated as the core while PEG segments are distributed on the surface as the shell of the AIE Pdots in water. Therefore this method was feasible to enable the application o f hydrophobic fluorophores in a biocompatible environment by taking advantage of the nanoparticles. The AIE Pdots possessed high chemical stability due to the covalent bond between AIE luminogens and PCL-b-PEG. In addition, At a neutral pH value (around 7), the ζ potentials of 28 and 27 Pdots were about -40 and 7 mV respectively, which further proved that 28 Pdots had higher colloidal stability than 27 Pdots. To evaluate the performance of specific cellular imaging of these AIE Pdots, HeLa cells (human cervical epithelioid carcinoma) with an over-expressing folate receptor (FR) were chosen for the imaging experiments as target cells. Meanwhile, 3T3-L1 cells (mice preadipocytes) with low expression of folate receptors were chosen for control experiments. HeLa cancer cells and 3T3-L1 cells were incubated in culture medium with two AIE Pdot suspensions at a concentration of 0.16 mg/mL. There were almost no fluorescence found when 27 Pdots were incubated. In contrast, 28 Pdots are effectively internalized in the cytoplasm of HeLa cells by endocytosis. In 2007, Prasad and co-workers (43) developed a dye, 9,10-bis[4′-(4″aminostyryl)styryl]anthracene derivative (BDSA), which has been shown to enhance one- and two-photon fluorescence without any intermolecular quenching effect (Figure 9), which enables remarkable signal improvement by raising the BDSA loading density in the composite nanoparticle. It has been shown by in-vitro cell experiments that the optimum loading level of BDSA, in terms of uptake efficiency and intracellular fluorescence signal, which exists at around 30–40 wt % with respect to the organically modified silica (ORMOSIL) particle matrix. These BDSA/ORMOSIL composite nanoparticles were anticipated to provide a promising pathway to achieve a significant breakthrough in developing two-photon fluorescent probes for biomedical applications due to the advantages 131 Fujiki et al.; Aggregation-Induced Emission: Materials and Applications Volume 1 ACS Symposium Series; American Chemical Society: Washington, DC, 2016.


of two-photon properties, noninvasive cellular uptake and surface functionality for labeling. Highly emissive folate functionalized fluorescent silica nanoparticles (FFSNPs) with an DSA core and a folic acid-functionalized silica shell has been successfully developed (44). To covalently bind the DSA to silica nanoparticles (SNPs) at molecular level, we employed 3-chloropropyltriethoxysilane (CPS) as a chemical linker. (Figure 10) TEM and field-emission scanning electron microscopy (FE-SEM) images indicate that the FFSNPs are well formed spherical particles with a uniform diameter around 60 nm.

Figure 9. a) Chemical structure of BDSA and the photographs show two-photon excited fluorescence of THF solution and nanocrystal dispersion stabilized in AOT/1-butanol/water at the same concentration (excited at 775 nm). b) scheme for the two-photon excited ORMOSIL nanoparticles used for near-IR cell imaging. Reprinted with permission from ref. (43), Copyright 2007 Wiley-VCH. All these nanoparticles possess appreciable surface charges and thus good colloidal stability, due to the negative charges of their surface. Taken upon exposure to the irradiation under a UV light of 365 nm, the solution of DSA-Si and the suspensions of SNPs almost have no light emission, and intense yellow light is emitted from FFSNPs. This visual observation further supports the idea that the intra-molecular rotations of DSA-Si are restricted by the covalent melding of the AIE fluorogen with the silica matrix causing a burst in light emission. FFSNPs are taken up nondestructively by mammalian cells via a specialized endocytosis pathway mediated by folate receptors (FR). With the folic acid-functionalized surface, FFSNPs should have a high binding affinity to FR. After binding to FR on the cancer cell surface, FFSNPs are seen to internalize and traffic to intracellular compartments called endosomes. Moreover, the obtained FFSNPs show specific 132 Fujiki et al.; Aggregation-Induced Emission: Materials and Applications Volume 1 ACS Symposium Series; American Chemical Society: Washington, DC, 2016.


targeting ability to cancer cells that overexpress the folate receptor, while avoiding normal cells that do not overexpress this receptor. Taking into account the mesoporous structure of FFSNPs, encapsulating anticancer drugs to the FFSNPs could provide a promising material for cancer diagnosis and treatment.

Figure 10. a) Scheme of FFSNPs. b) TEM and CLSM image s of mono dispersed FFSNPs. c) Solution and suspensions of 3, SNPs and FFSNPs in ethanol; photograph taken upon irradiation with a UV light of 365 nm. d) Folate-mediated delivery of FFSNPs to folate receptor-positive cancer cells. A fraction o f the FFSNPs will traffic into the cancer cells by receptor-mediated endocytosis (left side of diagram), while the remainder will remain on the cell surfaces (right side o f diagram), two types o f strategies can be envisioned. Reprinted with permission from ref. (44), Copyright 2013 The Royal Society of Chemistry.

Summary In this chapter, we reviewed recent studies on AIE of DSA derivatives and their applications. Through such studies, we present that various DSA derivatives possess a typical AIE feature, which non-luminescent molecules in solutions are induced to emit by aggregation formation. These fascinating molecules have been explored the potential applications as solid-state emitters, chemical sensors, biological probes and smart materials. We believe that AIE will darw a new rosy vista for luminescence materials. 133 Fujiki et al.; Aggregation-Induced Emission: Materials and Applications Volume 1 ACS Symposium Series; American Chemical Society: Washington, DC, 2016.

Acknowledgments We gratefully acknowledge our colleagues who contributed to this work as co-authors in the publications that were reviewed here. This work was supported by (2013CB834701), the Natural Science Foundation of China (No. 51373063, 51573068, 21221063) ,Program for Chang Jiang Scholars and Innovative Research Team in University (No. IRT101713018), and Program for Changbaishan Scholars of Jilin Province.


References 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13.

14. 15. 16. 17. 18. 19.

Mei, J.; Leung, N. L. C.; Kwok, R. T. K.; Lam, J. W. Y.; Tang, B. Z. Chem. Rev. 2015, 115, 11718–11940. Borisov, S. M.; Wolfbeis, O. S. Chem. Rev. 2008, 108, 423–461. Chen, L.; Xu, S.; McBranch, D.; Whitten, D. J. Am. Chem. Soc. 2000, 122, 9302–9303. Taylor, P. N.; O’Connell, M. J.; McNeill, L. A.; Hall, M. J.; Aplin, R. T.; Anderson, H. L. Angew. Chem. Int. Ed. 2000, 39, 3456–3460. Luo, J.; Xie, Z.; Lam, J. W. Y.; Cheng, L.; Chen, H.; Qiu, C.; Kwok, H. S.; Zhan, X.; Liu, Y.; Zhu, D.; Tang, B. Z. Chem. Commun. 2001, 1740–1741. Tang, B. Z.; Zhan, X.; Yu, G.; Sze Lee, P. P.; Liu, Y.; Zhu, D. J. Mater. Chem. 2001, 11, 2974–2978. Itami, K.; Ohashi, Y.; Yoshida, J.-i. J. Org. Chem. 2005, 70, 2778–2792. Hong, Y.; Lam, J. W. Y.; Tang, B. Z. Chem. Soc. Rev. 2011, 40, 5361–5388. Hong, Y.; Lam, J. W. Y.; Tang, B. Z. Chem. Commun. 2009, 29, 4332–4353. He, J.; Xu, B.; Chen, F.; Xia, H.; Li, K.; Ye, L.; Tian, W. J. Phys. Chem. C 2009, 113, 9892–9899. Xu, B.; Fang, H.; Dong, Y.; Chen, F.; Chen, Q.; Sun, H.; Tian, W. New J. Chem. 2010, 34, 1838–1842. Dong, Y.; Xu, B.; Zhang, J.; Lu, H.; Wen, S.; Chen, F.; He, J.; Li, B.; Ye, L.; Tian, W. CrystEngComm 2012, 14, 6593–6598. Hu, R.; Lager, E.; Aguilar-Aguilar, A.; Liu, J.; Lam, J. W. Y.; Sung, H. H. Y.; Williams, I. D.; Zhong, Y.; Wong, K. S.; Peña-Cabrera, E.; Tang, B. Z. The J. Phys. Chem. C 2009, 113, 15845–15853. Xu, B.; He, J.; Dong, Y.; Chen, F.; Yu, W.; Tian, W. Chem. Commun. 2011, 47, 6602–6604. Xu, B.; Zhang, J.; Fang, H.; Ma, S.; Chen, Q.; Sun, H.; Im, C.; Tian, W. Polym. Chem. 2014, 5, 479–488. Nakatsuji, S. i.; Matsuda, K.; Uesugi, Y.; Nakashima, K.; Akiyama, S.; Katzer, G.; Fabian, W. J. Chem. Soc., Perkin Trans. 2 1991, 6, 861–867. Kim, S.; Zheng, Q.; He, G. S.; Bharali, D. J.; Pudavar, H. E.; Baev, A.; Prasad, P. N. Adv. Funct. Mater. 2006, 16, 2317–2323. Lu, H.; Xu, B.; Dong, Y.; Chen, F.; Li, Y.; Li, Z.; He, J.; Li, H.; Tian, W. Langmuir 2010, 26, 6838–6844. Dong, Y.; Xu, B.; Zhang, J.; Tan, X.; Wang, L.; Chen, J.; Lv, H.; Wen, S.; Li, B.; Ye, L.; Zou, B.; Tian, W. Angew. Chem. Int. Ed. 2012, 51, 10782–10785. 134 Fujiki et al.; Aggregation-Induced Emission: Materials and Applications Volume 1 ACS Symposium Series; American Chemical Society: Washington, DC, 2016.


20. Zhang, X.; Chi, Z.; Zhang, J.; Li, H.; Xu, B.; Li, X.; Liu, S.; Zhang, Y.; Xu, J. J. Phys. Chem. B 2011, 115, 7606–7611. 21. Li, H.; Zhang, X.; Chi, Z.; Xu, B.; Zhou, W.; Liu, S.; Zhang, Y.; Xu, J. Org. Lett. 2011, 13, 556–559. 22. Lu, H.; Su, F.; Mei, Q.; Zhou, X.; Tian, Y.; Tian, W.; Johnson, R. H.; Meldrum, D. R. J. Polym. Sci., Part A: Polym. Chem. 2012, 50, 890–899. 23. Lu, H.; Su, F.; Mei, Q.; Tian, Y.; Tian, W.; Johnson, R. H.; Meldrum, D. R. J. Mater. Chem. 2012, 22, 9890–9900. 24. Zhang, J.; Xu, B.; Chen, J.; Ma, S.; Dong, Y.; Wang, L.; Li, B.; Ye, L.; Tian, W. Adv Mater 2014, 26, 739–745. 25. Chen, J.; Ma, S.; Zhang, J.; Li, B.; Xu, B.; Tian, W. ACS Photonics 2015, 2, 313–318. 26. Cornil, J.; Beljonne, D.; Calbert, J. P.; Brédas, J. L. Adv Mater 2001, 13, 1053–1067. 27. Wu, D.-E.; Wang, M.-N.; Luo, Y.-H.; Wen, G.-J.; Sun, B.-W. CrystEngComm 2015, 17, 9228–9239. 28. Xu, B.; Zhang, J.; Fang, H.; Ma, S.; Chen, Q.; Sun, H.; Im, C.; Tian, W. Polym. Chem. 2014, 5, 479–488. 29. Dong, Y.; Xu, B.; Zhang, J.; Tan, X.; Wang, L.; Chen, J.; Lv, H.; Wen, S.; Li, B.; Ye, L.; Zou, B.; Tian, W. Angew. Chem., Int. Ed. Engl. 2012, 51, 10782–10785. 30. Zhang, X.; Chi, Z.; Li, H.; Xu, B.; Li, X.; Zhou, W.; Liu, S.; Zhang, Y.; Xu, J. Chem. - Asian J. 2011, 6, 808–811. 31. Zhang, J.; Chen, J.; Xu, B.; Wang, L.; Ma, S.; Dong, Y.; Li, B.; Ye, L.; Tian, W. Chem. Commun. (Camb) 2013, 49, 3878–3880. 32. Dong, Y.; Zhang, J.; Tan, X.; Wang, L.; Chen, J.; Li, B.; Ye, L.; Xu, B.; Zou, B.; Tian, W. J. Mater. Chem. C 2013, 1, 7554–7559. 33. Ma, K.; Li, X.; Xu, B.; Tian, W. Anal. Methods 2014, 6, 2338–2342. 34. Li, X.; Xu, B.; Lu, H.; Wang, Z.; Zhang, J.; Zhang, Y.; Dong, Y.; Ma, K.; Wen, S.; Tian, W. Anal. Methods 2013, 5, 438–441. 35. Li, X.; Ma, K.; Lu, H.; Xu, B.; Wang, Z.; Zhang, Y.; Gao, Y.; Yan, L.; Tian, W. Anal. Bioanal. Chem. 2014, 406, 851–858. 36. Ma, K.; Wang, H.; Li, X.; Xu, B.; Tian, W. Anal. Bioanal. Chem. 2015, 407, 2625–2630. 37. Li, X.; Ma, K.; Zhu, S.; Yao, S.; Liu, Z.; Xu, B.; Yang, B.; Tian, W. Anal. Chem. 2014, 86, 298–303. 38. Zhang, X.; Zhang, X.; Wang, S.; Liu, M.; Tao, L.; Wei, Y. Nanoscale 2013, 5, 147–150. 39. Wang, Z.; Yan, L.; Zhang, L.; Chen, Y.; Li, H.; Zhang, J.; Zhang, Y.; Li, X.; Xu, B.; Fu, X.; Sun, Z.; Tian, W. Polym. Chem. 2014, 5, 7013–7020. 40. Lu, H.; Su, F.; Mei, Q.; Zhou, X.; Tian, Y.; Tian, W.; Johnson, R. H.; Meldrum, D. R. J. Polym. Sci., Part A: Polym. Chem. 2012, 50, 890–899. 41. Lu, H.; Su, F.; Mei, Q.; Tian, Y.; Tian, W.; Johnson, R. H.; Meldrum, D. R. J. Mater. Chem. 2012, 22, 9890–9900. 42. Zhang, Y.; Chen, Y.; Li, X.; Zhang, J.; Chen, J.; Xu, B.; Fu, X.; Tian, W. Polym. Chem. 2014, 5, 3824–3830. 135 Fujiki et al.; Aggregation-Induced Emission: Materials and Applications Volume 1 ACS Symposium Series; American Chemical Society: Washington, DC, 2016.


43. Kim, S.; Pudavar, H. E.; Bonoiu, A.; Prasad, P. N. Adv. Mater. 2007, 19, 3791–3795. 44. Wang, Z.; Xu, B.; Zhang, L.; Zhang, J.; Ma, T.; Zhang, J.; Fu, X.; Tian, W. Nanoscale 2013, 5, 2065–2072.


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