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2016 Volume 74 Issue 11
2016, 74(11): 857-858
doi: 10.6023/A1611E001
Abstract:
2016, 74(11): 865-870
doi: 10.6023/A16070372
Abstract:
By utilizing the special sp3 hybridization of tetraphenylmethane to break and control the intramolecular conjugation, and using silicon atom to replace the carbon atom in tetraphenylsilane, six molecules of C-4pTPE, C-4mTPE, C-4triPE, Si-4pTPE, Si-4mTPE, and Si-4triPE, were designed and successfully obtained, with tetraphenylethylene (TPE) and triphenylethylene (triPE) introduced to the core of tetraphenylmethane or tetraphenylsilane as rotors. These six molecules all possess typical aggregation induced emission (AIE) properties, they are all nearly nonemissive when readily dissolved in pure THF, but with the water fraction increasing, the PL intensity gradually increased. Due to their good AIE properties and thermal stability, they were fabricated in OLED devices by the solution process conveniently, with the maximum luminance (Lmax), maximum current efficiency (ηC, max), maximum power efficiency (ηp, max) and maximum external quantum efficiency (ηext, max) at 1730 cd·m-2, 2.21 cd·A-1, 0.77 lm·W-1 and 1.01%, respectively.
By utilizing the special sp3 hybridization of tetraphenylmethane to break and control the intramolecular conjugation, and using silicon atom to replace the carbon atom in tetraphenylsilane, six molecules of C-4pTPE, C-4mTPE, C-4triPE, Si-4pTPE, Si-4mTPE, and Si-4triPE, were designed and successfully obtained, with tetraphenylethylene (TPE) and triphenylethylene (triPE) introduced to the core of tetraphenylmethane or tetraphenylsilane as rotors. These six molecules all possess typical aggregation induced emission (AIE) properties, they are all nearly nonemissive when readily dissolved in pure THF, but with the water fraction increasing, the PL intensity gradually increased. Due to their good AIE properties and thermal stability, they were fabricated in OLED devices by the solution process conveniently, with the maximum luminance (Lmax), maximum current efficiency (ηC, max), maximum power efficiency (ηp, max) and maximum external quantum efficiency (ηext, max) at 1730 cd·m-2, 2.21 cd·A-1, 0.77 lm·W-1 and 1.01%, respectively.
2016, 74(11): 871-876
doi: 10.6023/A16080415
Abstract:
It is known that carboxylesterase (CaE) are a group of isoenzymes commonly distributed in mammalian organs, and they can catalyze the hydrolysis of carboxyl ester. As a result, they play an important role in detoxification of narcotics or chemical toxin clearance. Moreover, they serve as important drug candidates for protein-based therapeutics or drug targets for chemotherapeutic prodrug activation. It is reported recently that human plasma carboxylesterase can be a novel biomarker candidate for hepatocellular carcinoma. Therefore, establishing a reliable fluorescent system for detecting carboxylesterase is of great importance in terms of biochemical studies as well as clinical applications. Herein, we report a new fluorometric turn-on assay for carboxylesterase activity and inhibitor screening with compound 1 by utilizing the aggregation-induced emission (AIE) feature of tetraphenylethylene (TPE) molecules. The sensing mechanism is illustrated in Figure 1 and explains as follows:(i) the pyridinium moiety may render compound 1 water-soluble. As a result it is anticipated that compound 1 is weakly emissive in aqueous solutions according to previous studies; (ii) the incubation of carboxylesterase with compound 1 can result in cleaving the carboxylic ester bond, followed by hydrolysis and 1, 6-elimination of p-quinonemethide to yield the p-pyridine substituted TPE (TPE-Py). TPE-Py is not soluble in aqueous solutions, thus aggregation will occur and turn on the fluorescence of TPE moiety based on the AIE feature of TPE compounds. In this way, compound 1 can be employed for the fluorescence turn-on assay for carboxylesterase activity. The results reveal that the buffer solution of compound 1 emitted very weakly. However, the green fluorescence emission was switched on after addition of carboxylesterase. Carboxylesterase at concentrations as low as 5.67×10-5 U/mL can be assayed with compound 1. Further results clearly indicate that compound 1 can be utilized not only for carboxylesterase activity assay but also for the corresponding inhibitor screening. More importantly, this probe can be applied for detection of carboxylesterases in living cells.
It is known that carboxylesterase (CaE) are a group of isoenzymes commonly distributed in mammalian organs, and they can catalyze the hydrolysis of carboxyl ester. As a result, they play an important role in detoxification of narcotics or chemical toxin clearance. Moreover, they serve as important drug candidates for protein-based therapeutics or drug targets for chemotherapeutic prodrug activation. It is reported recently that human plasma carboxylesterase can be a novel biomarker candidate for hepatocellular carcinoma. Therefore, establishing a reliable fluorescent system for detecting carboxylesterase is of great importance in terms of biochemical studies as well as clinical applications. Herein, we report a new fluorometric turn-on assay for carboxylesterase activity and inhibitor screening with compound 1 by utilizing the aggregation-induced emission (AIE) feature of tetraphenylethylene (TPE) molecules. The sensing mechanism is illustrated in Figure 1 and explains as follows:(i) the pyridinium moiety may render compound 1 water-soluble. As a result it is anticipated that compound 1 is weakly emissive in aqueous solutions according to previous studies; (ii) the incubation of carboxylesterase with compound 1 can result in cleaving the carboxylic ester bond, followed by hydrolysis and 1, 6-elimination of p-quinonemethide to yield the p-pyridine substituted TPE (TPE-Py). TPE-Py is not soluble in aqueous solutions, thus aggregation will occur and turn on the fluorescence of TPE moiety based on the AIE feature of TPE compounds. In this way, compound 1 can be employed for the fluorescence turn-on assay for carboxylesterase activity. The results reveal that the buffer solution of compound 1 emitted very weakly. However, the green fluorescence emission was switched on after addition of carboxylesterase. Carboxylesterase at concentrations as low as 5.67×10-5 U/mL can be assayed with compound 1. Further results clearly indicate that compound 1 can be utilized not only for carboxylesterase activity assay but also for the corresponding inhibitor screening. More importantly, this probe can be applied for detection of carboxylesterases in living cells.
2016, 74(11): 877-884
doi: 10.6023/A16070348
Abstract:
Tetraphenylethene-containing diacetylenes are synthesized and their homopolymerizations are catalyzed by CuCl in o-dichlorobenzene, furnishing linear polyynes in high isolated yields. All polymers possess good solubility in common organic solvents and enjoy high thermal stability. Whereas they are practically non-emissive when molecularly dissolved in good solvents, they become highly emissive when aggregated as nanoparticle suspensions in poor solvents or fabricated into thin films in the solid state, demonstrating a novel phenomenon of aggregation-induced emission. The polymers are highly transparent, allowing almost all light in the entire visible spectral region to transmit through. Thin films of the polymers show high refractive indices (n=1.7787~1.6543) in the wavelength region of 400~1700 nm and very low chromatic aberrations (D'=0.0003). Their n values can be modulated and their thin films can be crosslinked by UV irradiation, generating fluorescent patterns with high resolutions.
Tetraphenylethene-containing diacetylenes are synthesized and their homopolymerizations are catalyzed by CuCl in o-dichlorobenzene, furnishing linear polyynes in high isolated yields. All polymers possess good solubility in common organic solvents and enjoy high thermal stability. Whereas they are practically non-emissive when molecularly dissolved in good solvents, they become highly emissive when aggregated as nanoparticle suspensions in poor solvents or fabricated into thin films in the solid state, demonstrating a novel phenomenon of aggregation-induced emission. The polymers are highly transparent, allowing almost all light in the entire visible spectral region to transmit through. Thin films of the polymers show high refractive indices (n=1.7787~1.6543) in the wavelength region of 400~1700 nm and very low chromatic aberrations (D'=0.0003). Their n values can be modulated and their thin films can be crosslinked by UV irradiation, generating fluorescent patterns with high resolutions.
2016, 74(11): 885-892
doi: 10.6023/A16080435
Abstract:
Organic luminescent materials with aggregation-induced emission (AIE) characteristics have attracted much attention among the scientists in the fields of optoelectronic devices and fluorescence biotechnology. AIE materials overcomes the aggregation-caused quenching problem of traditional organic fluorescent compounds, which possess high fluorescence quantum efficiency in the aggregated states. Thanks to the great research effort of worldwide scientists, a large variety of AIE materials have been developed and the underlying mechanism has been rapidly explored. The deep understanding of the structure-property relationship of AIE compounds is still in an urgent demand for the design of new materials. In this work, based on the classical propeller-shaped AIEgen, tetraphenylethene (TPE), we designed and synthesized a series of electron donor/acceptor-containing alkynone derivatives with AIE feature such as cyano, nitro, butyl and butoxyl groups-substituted alkynone derivatives. Their chemical structures have been fully characterized by 1H NMR, 13C NMR, IR, and HRMS spectra, providing satisfactory analysis results. Their photophysical properties are systematically studied and the effect of substitution groups on the emission maximum, emission efficiency, as well as AIE property are discussed, respectively. Their emission maxima are located at 511~565 nm with the fluorescence quantum yields of up to 31% in the aggregated states in THF/water mixtures with high water content. The fluorescence intensity of the unsubstituted TPE-containing alkynone derivative in THF/H2O with φw=90% water content is 157 times higher than that in THF solution. It is suggested that both electron-donating and electron-withdrawing substitution groups on the terminal phenyl ring decrease the emission efficiency of the aggregated state and the introduction of nitro group dramatically quenches the emission while redshifts the emission maximum. Most importantly, the alkynone groups in these compounds can selectively coordinate with Pd2+ among a large variety of metal ions, which quench the emission of the nanoaggregates and possess high sensitivity towards Pd2+, demon-strating the potential application as an efficient Pd2+ fluorescent sensor.
Organic luminescent materials with aggregation-induced emission (AIE) characteristics have attracted much attention among the scientists in the fields of optoelectronic devices and fluorescence biotechnology. AIE materials overcomes the aggregation-caused quenching problem of traditional organic fluorescent compounds, which possess high fluorescence quantum efficiency in the aggregated states. Thanks to the great research effort of worldwide scientists, a large variety of AIE materials have been developed and the underlying mechanism has been rapidly explored. The deep understanding of the structure-property relationship of AIE compounds is still in an urgent demand for the design of new materials. In this work, based on the classical propeller-shaped AIEgen, tetraphenylethene (TPE), we designed and synthesized a series of electron donor/acceptor-containing alkynone derivatives with AIE feature such as cyano, nitro, butyl and butoxyl groups-substituted alkynone derivatives. Their chemical structures have been fully characterized by 1H NMR, 13C NMR, IR, and HRMS spectra, providing satisfactory analysis results. Their photophysical properties are systematically studied and the effect of substitution groups on the emission maximum, emission efficiency, as well as AIE property are discussed, respectively. Their emission maxima are located at 511~565 nm with the fluorescence quantum yields of up to 31% in the aggregated states in THF/water mixtures with high water content. The fluorescence intensity of the unsubstituted TPE-containing alkynone derivative in THF/H2O with φw=90% water content is 157 times higher than that in THF solution. It is suggested that both electron-donating and electron-withdrawing substitution groups on the terminal phenyl ring decrease the emission efficiency of the aggregated state and the introduction of nitro group dramatically quenches the emission while redshifts the emission maximum. Most importantly, the alkynone groups in these compounds can selectively coordinate with Pd2+ among a large variety of metal ions, which quench the emission of the nanoaggregates and possess high sensitivity towards Pd2+, demon-strating the potential application as an efficient Pd2+ fluorescent sensor.
2016, 74(11): 893-901
doi: 10.6023/A16080410
Abstract:
Aggregation-induced emission (AIE) active compounds and materials have become one of the hottest research topics worldwide, due to their unprecedented merits such as ultra-high fluorescence quantum efficiencies as aggregates or in solid state. Up to now, it is still extremely crucial and fundamental to expand the AIE-genic molecular systems for this research area. Here, we prepared two fluoranthene-modified tetraphenylethene (TPE) derivatives, TPE-FA and TPE-DFA, through the Suzuki-Miyaura coupling between boronate-bearing TPE and bromo-bearing fluoranthene under mild reaction condition. The conjugation between fluoranthene and TPE moieties assures that the as-prepared TPE-FA and TPE-DFA both possess aggrega-tion-enhanced emission (AEE) characteristics. The emission maximum of TPE-FA and TPE-DFA as aggregates in THF/water mixtures is at 477 nm and 494 nm, and the absolute quantum yields of the two compounds in solid films are as high as 74.1% and 40.4%, respectively. They can be utilized as fluorescent probes for picric acid with high sensitivity. Their quenching coef-ficients can be as high as 4×104 L·mol-1, while their detection limits can be lower than 1 μg·g-1. These AEE-active molecules are promising to act as fluorescent probes in the detection of other nitro-substituted electron-deficient molecules.
Aggregation-induced emission (AIE) active compounds and materials have become one of the hottest research topics worldwide, due to their unprecedented merits such as ultra-high fluorescence quantum efficiencies as aggregates or in solid state. Up to now, it is still extremely crucial and fundamental to expand the AIE-genic molecular systems for this research area. Here, we prepared two fluoranthene-modified tetraphenylethene (TPE) derivatives, TPE-FA and TPE-DFA, through the Suzuki-Miyaura coupling between boronate-bearing TPE and bromo-bearing fluoranthene under mild reaction condition. The conjugation between fluoranthene and TPE moieties assures that the as-prepared TPE-FA and TPE-DFA both possess aggrega-tion-enhanced emission (AEE) characteristics. The emission maximum of TPE-FA and TPE-DFA as aggregates in THF/water mixtures is at 477 nm and 494 nm, and the absolute quantum yields of the two compounds in solid films are as high as 74.1% and 40.4%, respectively. They can be utilized as fluorescent probes for picric acid with high sensitivity. Their quenching coef-ficients can be as high as 4×104 L·mol-1, while their detection limits can be lower than 1 μg·g-1. These AEE-active molecules are promising to act as fluorescent probes in the detection of other nitro-substituted electron-deficient molecules.
2016, 74(11): 910-916
doi: 10.6023/A16070342
Abstract:
Fluorophores with aggregation-induced emission (AIE) feature are favorable tools for both chemical sensing and bioimaging. Inflammatory cells excessively express hydrolytic enzymes (esterase, protease and phosphatase) and are usually exposed to elevated levels of reactive oxygen species (ROS). Overexpression of ROS and the insufficient neutralization by antioxidants may give rise to the development of oxidative stress and chronic inflammation. Taurine (2-aminoethanesulfonic acid), as an effective antioxidant, can protect tissues from oxidative stress associated with various inflammatory diseases. Moreover, it has been recently reported that the incorporation of taurine can amazingly boost the cellular uptake for intracellular accumulation. Herein, we designed and synthesized a new near-infrared (NIR) AIE fluorophore DTPE. We anticipate that, the combination of the hydrophilic taurine with the NIR AIE fluorophore through an ester bond could be a remarkable method for extending the applications of AIE-active fluorophores e.g. as a trackable visualized therapeutic system featuring both imaging esterase-activated taurine release and ROS scavenging. Then we obtained the AIE probe system DTPE-Tau by incorporating taurine with the fluorophore through carbamate bond. The hydrophilic taurine moiety endows the system with enhanced water solubility and cellular uptake ability. The system is characterized by several advantages, such as large Stokes shift (225 nm), low cytotoxicity, and good photostability. The ester bond can be hydrolysed by the overexpressed esterase in inflammatory cells, thereby releasing a taurine moiety for ROS scavenging and in the meantime the AIE fluorophore moiety acts as a reporter for tracking esterase-activated taurine release. The enhancement of emission could serve as the reporting signal. The release rate is determined to be 75% for esterase at 0.05 mg/mL, calculated based on the fluorescence-intensity working curve. Also, the probe has been successfully utilized for tracking esterase-activated release of taurine and scavenging intracellular ROS in RAW264.7 cell line, which shows great potential for trackable visualized therapy.
Fluorophores with aggregation-induced emission (AIE) feature are favorable tools for both chemical sensing and bioimaging. Inflammatory cells excessively express hydrolytic enzymes (esterase, protease and phosphatase) and are usually exposed to elevated levels of reactive oxygen species (ROS). Overexpression of ROS and the insufficient neutralization by antioxidants may give rise to the development of oxidative stress and chronic inflammation. Taurine (2-aminoethanesulfonic acid), as an effective antioxidant, can protect tissues from oxidative stress associated with various inflammatory diseases. Moreover, it has been recently reported that the incorporation of taurine can amazingly boost the cellular uptake for intracellular accumulation. Herein, we designed and synthesized a new near-infrared (NIR) AIE fluorophore DTPE. We anticipate that, the combination of the hydrophilic taurine with the NIR AIE fluorophore through an ester bond could be a remarkable method for extending the applications of AIE-active fluorophores e.g. as a trackable visualized therapeutic system featuring both imaging esterase-activated taurine release and ROS scavenging. Then we obtained the AIE probe system DTPE-Tau by incorporating taurine with the fluorophore through carbamate bond. The hydrophilic taurine moiety endows the system with enhanced water solubility and cellular uptake ability. The system is characterized by several advantages, such as large Stokes shift (225 nm), low cytotoxicity, and good photostability. The ester bond can be hydrolysed by the overexpressed esterase in inflammatory cells, thereby releasing a taurine moiety for ROS scavenging and in the meantime the AIE fluorophore moiety acts as a reporter for tracking esterase-activated taurine release. The enhancement of emission could serve as the reporting signal. The release rate is determined to be 75% for esterase at 0.05 mg/mL, calculated based on the fluorescence-intensity working curve. Also, the probe has been successfully utilized for tracking esterase-activated release of taurine and scavenging intracellular ROS in RAW264.7 cell line, which shows great potential for trackable visualized therapy.
2016, 74(11): 917-922
doi: 10.6023/A16080430
Abstract:
Near-infrared fluorescence signals are highly desirable to acheieve high resolution in biological imaging. We encapsulated hydrophobic AIE (aggregation-induced emission) fluorophores into the biocompatible Pluronic F-127 NPs for cellular imaging and efficiently enhance the near-infrared AIE fluorophore emission. AIE molecule 2-(4-bromophenyl)-3-(4-(4-(diphenylamino) styryl) phenyl) fumaronitrile (TPABDFN) with near-infrared emission was synthesized and selected as the fluorescence resonance energy transfer (FRET) acceptor. (2-p-tolylethene-1, 1, 2-triyl) tribenzene (TPE-Me) was a blue-emitting AIE molecule, which spectrum was matching with TPABDFN. TPE-Me@F127 NPs emission was 480 nm, TPABDFN@F127 NPs maximum absorption wavelength was also 480 nm, that the absorption had a large area of overlapping with the TPE-Me@F127 NPs emission spectrum and leaded to efficient energy transfer, so TPE-Me was selected as the FRET donor. By encapsulating both TPE-Me donor and TPABDFN acceptor simultaneously within the NPs, a significant FRET effect was induced. FRET pairs of different ratios was co-encapsulated into the F127 NPs to optimize the fluorescence signals. The maximum of fluorescence quantum yield was 19.9%, energy transfer efficiency was 43.5%. TPABDFN@F127 NPs only had weak fluorescence, but the TPABDFN/TPE-Me@F127 NPs showed bright fluorescence signal. Fluorescence resonance energy transfer contributed to the notable increase of acceptor emission The fluorescence quantum yield had 10-fold enhancement of the TPABDFN. In addition, the obtained TPABDFN/TPE-Me@F127 NPs showed a large Stokes shift of 265 nm, which can be used to avoid the interference between excitation and emission light, as well as the near-infrared emission spectrum away from the organism auto-fluorescence, which was beneficial for the bio-application. Fluorescent probe emission in the far red/near-infrared (FR/NIR) (650~900 nm) region for biological detection also can greatly reduce the damage to living body. And TPABDFN/TPE-Me@F127 NPs had low cytotoxicity, good biocompatibility, stability and anti-photobleaching. The TPABDFN/TPE-Me@F127 NPs achieved good imaging result on HepG2 cell cytoplasm.
Near-infrared fluorescence signals are highly desirable to acheieve high resolution in biological imaging. We encapsulated hydrophobic AIE (aggregation-induced emission) fluorophores into the biocompatible Pluronic F-127 NPs for cellular imaging and efficiently enhance the near-infrared AIE fluorophore emission. AIE molecule 2-(4-bromophenyl)-3-(4-(4-(diphenylamino) styryl) phenyl) fumaronitrile (TPABDFN) with near-infrared emission was synthesized and selected as the fluorescence resonance energy transfer (FRET) acceptor. (2-p-tolylethene-1, 1, 2-triyl) tribenzene (TPE-Me) was a blue-emitting AIE molecule, which spectrum was matching with TPABDFN. TPE-Me@F127 NPs emission was 480 nm, TPABDFN@F127 NPs maximum absorption wavelength was also 480 nm, that the absorption had a large area of overlapping with the TPE-Me@F127 NPs emission spectrum and leaded to efficient energy transfer, so TPE-Me was selected as the FRET donor. By encapsulating both TPE-Me donor and TPABDFN acceptor simultaneously within the NPs, a significant FRET effect was induced. FRET pairs of different ratios was co-encapsulated into the F127 NPs to optimize the fluorescence signals. The maximum of fluorescence quantum yield was 19.9%, energy transfer efficiency was 43.5%. TPABDFN@F127 NPs only had weak fluorescence, but the TPABDFN/TPE-Me@F127 NPs showed bright fluorescence signal. Fluorescence resonance energy transfer contributed to the notable increase of acceptor emission The fluorescence quantum yield had 10-fold enhancement of the TPABDFN. In addition, the obtained TPABDFN/TPE-Me@F127 NPs showed a large Stokes shift of 265 nm, which can be used to avoid the interference between excitation and emission light, as well as the near-infrared emission spectrum away from the organism auto-fluorescence, which was beneficial for the bio-application. Fluorescent probe emission in the far red/near-infrared (FR/NIR) (650~900 nm) region for biological detection also can greatly reduce the damage to living body. And TPABDFN/TPE-Me@F127 NPs had low cytotoxicity, good biocompatibility, stability and anti-photobleaching. The TPABDFN/TPE-Me@F127 NPs achieved good imaging result on HepG2 cell cytoplasm.
2016, 74(11): 923-928
doi: 10.6023/A16080433
Abstract:
High performance mechanochromic luminescent (MCL) materials exhibiting multicolored emission switching or high contrast emission color and efficiency have seldom been reported despite their potential application to improve the complexity of anti-fake or increase the density of optical data storage. Through combination of the large conjugation core and peripheral phenyl rings, we designed and synthesized phenyltolyldibenzofulvene (1). Luminogen 1 exhibits aggregation induced emission (AIE) and crystallization enhanced emission (CEE). Luminogen 1 can form blue (1CB, 465 nm, Φ=14.6%) and blue-green (1CA, 485 nm, Φ=13.9%) emissive crystals through slow solvent evaporation of chloroform/hexane and 1, 2-dichlorethane/hexane, respectively, and its amorphous solid (1Am, 525 nm, Φ=2.1%) emits dark yellow green light. The propeller-like conformation of 1 affords loose packing pattern and facilitates the morphology tuning in the solid state. Thus, emission of 1 can be switched reversibly among blue, blue-green and yellow-green through modulation of morphology by mechanical stimuli, heating or solvent fuming. Moreover, the mechanochromic luminescence of 1 affords its potential application in optical recording. Ground powder of 1 was dispersed on weighing paper, and a yellow-green emissive paper was obtained. The paper can be transformed to blue and blue-green emissive through solvent fuming, and dark green letters on the blue and blue-green emissive paper could be obtained through writing with glass rod due to the amorphization of luminogen 1 in the written area. The letters can be erased through solvent fuming, heating or grinding, so the paper can be switched to blue, blue-green, or yellow-green emissive depending on the erasing method. Thus, following the strategy of combination of the large conjugation core and peripheral phenyl rings, the obtained luminogen exhibit multicolored MCL emission switching with high contrast. And the molecular design strategy for high performance MCL materials was further verified.
High performance mechanochromic luminescent (MCL) materials exhibiting multicolored emission switching or high contrast emission color and efficiency have seldom been reported despite their potential application to improve the complexity of anti-fake or increase the density of optical data storage. Through combination of the large conjugation core and peripheral phenyl rings, we designed and synthesized phenyltolyldibenzofulvene (1). Luminogen 1 exhibits aggregation induced emission (AIE) and crystallization enhanced emission (CEE). Luminogen 1 can form blue (1CB, 465 nm, Φ=14.6%) and blue-green (1CA, 485 nm, Φ=13.9%) emissive crystals through slow solvent evaporation of chloroform/hexane and 1, 2-dichlorethane/hexane, respectively, and its amorphous solid (1Am, 525 nm, Φ=2.1%) emits dark yellow green light. The propeller-like conformation of 1 affords loose packing pattern and facilitates the morphology tuning in the solid state. Thus, emission of 1 can be switched reversibly among blue, blue-green and yellow-green through modulation of morphology by mechanical stimuli, heating or solvent fuming. Moreover, the mechanochromic luminescence of 1 affords its potential application in optical recording. Ground powder of 1 was dispersed on weighing paper, and a yellow-green emissive paper was obtained. The paper can be transformed to blue and blue-green emissive through solvent fuming, and dark green letters on the blue and blue-green emissive paper could be obtained through writing with glass rod due to the amorphization of luminogen 1 in the written area. The letters can be erased through solvent fuming, heating or grinding, so the paper can be switched to blue, blue-green, or yellow-green emissive depending on the erasing method. Thus, following the strategy of combination of the large conjugation core and peripheral phenyl rings, the obtained luminogen exhibit multicolored MCL emission switching with high contrast. And the molecular design strategy for high performance MCL materials was further verified.
2016, 74(11): 929-934
doi: 10.6023/A16080427
Abstract:
Solution-based fluorescent probes usually need to be fabricated into fluorescent films for device application. The fabricated fluorescent films can have not only the original advantages of probes (e.g., high sensitivity and selectivity) but also several unique properties, such as tunable shape and size, recycling, non-invasion, good stability and portability, and real-time detection. However, the sensitivity of fluorescent films is often reduced by the aggregation-caused quenching (ACQ) effect during the film formation:fluorophores with high concentration inherently tend to aggregate through intermolecular π-π in-teractions. Moreover, the sensing performances of the fluorescent film are significantly influenced by the diffusion rate of analytes:the thicker the films, the slower the response time towards target molecules. Therefore, aggregation-induced emission (AIE) materials are urgently needed to be developed to overcome these shortcomings. On the other hand, excellent photostability could be better for the practical applications in the integrated sensor devices. However, most of the present AIEgens are π-conjugated organic molecules with poor ability against photobleaching. Interestingly, several fluorescent gold nanoclusters (AuNCs) with higher photostability were discovered to have AIE property. In this work, two kinds of negatively-charged fluorescent AuNCs were selected:bovine serum albumin capped AuNCs (BSA-AuNCs) and AIE-active glutathione capped AuNCs (GSH-AuNCs). Quartz glass slides were alternately dipped into a poly (allylamine) (PAH) solution and AuNCs solutions to fabricate GSH-AuNCs/PAH (yellow-emitting) and BSA-AuNCs/PAH (red-emitting) fluorescent ultrathin films, respectively. As expected, the photoluminescence quantum yield of GSH-AuNCs is two-fold higher in GSH-AuNCs/PAH ultrathin films than in solution. The fluorescence of (GSH-AuNCs/PAH)5 ultrathin film could be quenched effectively by 2, 4, 6-trinitrotoluene (TNT) in 10 min, while the fluorescence intensity of (BSA-AuNCs/PAH)25 ultrathin film remain almost unchanged. Based on this phenomenon, a novel ratio fluorescence sensing system was constructed by using (BSA-AuNCs/PAH)25 ultrathin film as control and (GSH-AuNCs/PAH)5 ultrathin film as the detection unit. The fluorescence intensity ratios (I565/I620) have a linear relationship with the log concentrations of TNT in the range of 10-6~10-9 mol/L with detection limit of 1.0×10-10 mol/L.
Solution-based fluorescent probes usually need to be fabricated into fluorescent films for device application. The fabricated fluorescent films can have not only the original advantages of probes (e.g., high sensitivity and selectivity) but also several unique properties, such as tunable shape and size, recycling, non-invasion, good stability and portability, and real-time detection. However, the sensitivity of fluorescent films is often reduced by the aggregation-caused quenching (ACQ) effect during the film formation:fluorophores with high concentration inherently tend to aggregate through intermolecular π-π in-teractions. Moreover, the sensing performances of the fluorescent film are significantly influenced by the diffusion rate of analytes:the thicker the films, the slower the response time towards target molecules. Therefore, aggregation-induced emission (AIE) materials are urgently needed to be developed to overcome these shortcomings. On the other hand, excellent photostability could be better for the practical applications in the integrated sensor devices. However, most of the present AIEgens are π-conjugated organic molecules with poor ability against photobleaching. Interestingly, several fluorescent gold nanoclusters (AuNCs) with higher photostability were discovered to have AIE property. In this work, two kinds of negatively-charged fluorescent AuNCs were selected:bovine serum albumin capped AuNCs (BSA-AuNCs) and AIE-active glutathione capped AuNCs (GSH-AuNCs). Quartz glass slides were alternately dipped into a poly (allylamine) (PAH) solution and AuNCs solutions to fabricate GSH-AuNCs/PAH (yellow-emitting) and BSA-AuNCs/PAH (red-emitting) fluorescent ultrathin films, respectively. As expected, the photoluminescence quantum yield of GSH-AuNCs is two-fold higher in GSH-AuNCs/PAH ultrathin films than in solution. The fluorescence of (GSH-AuNCs/PAH)5 ultrathin film could be quenched effectively by 2, 4, 6-trinitrotoluene (TNT) in 10 min, while the fluorescence intensity of (BSA-AuNCs/PAH)25 ultrathin film remain almost unchanged. Based on this phenomenon, a novel ratio fluorescence sensing system was constructed by using (BSA-AuNCs/PAH)25 ultrathin film as control and (GSH-AuNCs/PAH)5 ultrathin film as the detection unit. The fluorescence intensity ratios (I565/I620) have a linear relationship with the log concentrations of TNT in the range of 10-6~10-9 mol/L with detection limit of 1.0×10-10 mol/L.
2016, 74(11): 935-941
doi: 10.6023/A16080423
Abstract:
Nonconventional luminogens without classic aromatic or conjugated structures are attracting increasing interests owing to their fundamental importance and promising applications in diverse areas. Many of them even exhibit unique aggregation-induced emission (AIE) characteristics. The emission mechanism, however, remains under debate. Previously, we proposed the clustering-triggered emission (CTE) mechanism, namely the clustering of nonconventional chromophores and subsequent electron overlap to rationalize the emission behaviors of such luminogens. To further our understanding, herein, we designed and synthesized poly (N-hydroxysuccinimide methacrylate) (PNHSMA) without any aromatic structures, which was obtained by the radical polymerization of N-hydroxysuccinimide methacrylate (NHSMA) monomer in toluene at 65℃ utilizing azobisisobutyronitrile (AIBN) as initiator. And NHSMA was prepared through the elimination between N-hydroxysuccinimide (NHS) and methacryloyl chloride in the presence of triethylamine (Et3N). It is found that PNHSMA is virtually nonluminescent in dilute solutions (≤0.4 mg·mL-1) even at 77 K, but gets emissive in concentrated solutions (e.g. 40 mg·mL-1) with photoluminescence (PL) maxima at 434 and 485 nm at room temperature. Moreover, its solid powders emit intense blue light with multiple PL peaks upon UV irradiation, indicating its AIE nature and the formation of varying emission species. Further PL measurement of PNHSMA in dimethylformide (DMF) and DMF/acetone (good solvent/nonsolvent) mixtures duly verifies its AIE feature. Meanwhile, NHSMA monomer shows similar emission behaviors to those of PNHSMA, demonstrating concentration enhanced emission and AIE characteristics. In light of above results, it is assumed that NHSMA and its polymeric counterpart PNHSMA may share the similar emission mechanism. Single crystal structure of NHSMA reveals the conjugation of imide group and 3D intermolecular interactions of C=O…C=O (n-π, 3.072 Å), C=O…H-C (2.651, 2.642 Å) and C=O…C-H (3.099 Å). The emission of PNHSMA and NHSMA in concentrated solutions and solid states is thus ascribed to the clustering of imide and ester groups, which results in electronic interactions. The overlap of π and lone pair (n) electrons among C=O, N and O units, together with effective intermolecular interactions in the solid powders extend the conjugation and rigidify the molecular conformations, thus leading to boosted emissions. Such CTE mechanism might be well extended to other nonconventional systems and should be inspiring for the rational design of novel luminogens.
Nonconventional luminogens without classic aromatic or conjugated structures are attracting increasing interests owing to their fundamental importance and promising applications in diverse areas. Many of them even exhibit unique aggregation-induced emission (AIE) characteristics. The emission mechanism, however, remains under debate. Previously, we proposed the clustering-triggered emission (CTE) mechanism, namely the clustering of nonconventional chromophores and subsequent electron overlap to rationalize the emission behaviors of such luminogens. To further our understanding, herein, we designed and synthesized poly (N-hydroxysuccinimide methacrylate) (PNHSMA) without any aromatic structures, which was obtained by the radical polymerization of N-hydroxysuccinimide methacrylate (NHSMA) monomer in toluene at 65℃ utilizing azobisisobutyronitrile (AIBN) as initiator. And NHSMA was prepared through the elimination between N-hydroxysuccinimide (NHS) and methacryloyl chloride in the presence of triethylamine (Et3N). It is found that PNHSMA is virtually nonluminescent in dilute solutions (≤0.4 mg·mL-1) even at 77 K, but gets emissive in concentrated solutions (e.g. 40 mg·mL-1) with photoluminescence (PL) maxima at 434 and 485 nm at room temperature. Moreover, its solid powders emit intense blue light with multiple PL peaks upon UV irradiation, indicating its AIE nature and the formation of varying emission species. Further PL measurement of PNHSMA in dimethylformide (DMF) and DMF/acetone (good solvent/nonsolvent) mixtures duly verifies its AIE feature. Meanwhile, NHSMA monomer shows similar emission behaviors to those of PNHSMA, demonstrating concentration enhanced emission and AIE characteristics. In light of above results, it is assumed that NHSMA and its polymeric counterpart PNHSMA may share the similar emission mechanism. Single crystal structure of NHSMA reveals the conjugation of imide group and 3D intermolecular interactions of C=O…C=O (n-π, 3.072 Å), C=O…H-C (2.651, 2.642 Å) and C=O…C-H (3.099 Å). The emission of PNHSMA and NHSMA in concentrated solutions and solid states is thus ascribed to the clustering of imide and ester groups, which results in electronic interactions. The overlap of π and lone pair (n) electrons among C=O, N and O units, together with effective intermolecular interactions in the solid powders extend the conjugation and rigidify the molecular conformations, thus leading to boosted emissions. Such CTE mechanism might be well extended to other nonconventional systems and should be inspiring for the rational design of novel luminogens.
2016, 74(11): 942-948
doi: 10.6023/A16080406
Abstract:
A new A-D-A type pyrrolopyrrole-based derivative 4', 4"-(2, 5-diphenyl-pyrrolo[3, 2-b]pyrrole-1, 4-diyl) bis ([1, 1'-biphenyl]-4-carbonitrile) (DPPDC) was synthesized via Suzuki coupling reaction between 1, 4-bis (4-bromophenyl)-2, 5-diphenyl-1, 4-dihydropyrrolo[3, 2-b]pyrrole and 4-cyanophenylboronic acid. The fluorescent emission intensities of DPPDC in pure THF solution and lower fraction of water (φH2O≤60%) mixtures were weak at around 550 nm. When φH2O was 99% in THF/H2O mixtures, the emission was enhanced and blue-shifted at around 505 nm. The maximal fluorescent emission intensity of DPPDC was 11 times higher than that of in pure THF solution, indicating DPPDC exhibiting AIE property. It was also found that four different kinds of crystal structures of DPPDC was cultivated from CHCl2-Hexane, CHCl3-Hexane and CHCl3/Acetone-Hexane systems via solvent slow diffusion method. Four crystals respec-tively emitted blue, azure, green and turquoise at 467, 483, 496 and 493 nm, which manifested the polymorphism-dependent fluorescent emission property of DPPDC. Additionally, trifluoroacetic acid (TFA) could make the emitting color change from yellow to orange-red with as-prepared paper containing DPPDC due to the acid-base interaction. The obvious emitting color change of DPPDC can be used as a visual sensor to detect acid gas.
A new A-D-A type pyrrolopyrrole-based derivative 4', 4"-(2, 5-diphenyl-pyrrolo[3, 2-b]pyrrole-1, 4-diyl) bis ([1, 1'-biphenyl]-4-carbonitrile) (DPPDC) was synthesized via Suzuki coupling reaction between 1, 4-bis (4-bromophenyl)-2, 5-diphenyl-1, 4-dihydropyrrolo[3, 2-b]pyrrole and 4-cyanophenylboronic acid. The fluorescent emission intensities of DPPDC in pure THF solution and lower fraction of water (φH2O≤60%) mixtures were weak at around 550 nm. When φH2O was 99% in THF/H2O mixtures, the emission was enhanced and blue-shifted at around 505 nm. The maximal fluorescent emission intensity of DPPDC was 11 times higher than that of in pure THF solution, indicating DPPDC exhibiting AIE property. It was also found that four different kinds of crystal structures of DPPDC was cultivated from CHCl2-Hexane, CHCl3-Hexane and CHCl3/Acetone-Hexane systems via solvent slow diffusion method. Four crystals respec-tively emitted blue, azure, green and turquoise at 467, 483, 496 and 493 nm, which manifested the polymorphism-dependent fluorescent emission property of DPPDC. Additionally, trifluoroacetic acid (TFA) could make the emitting color change from yellow to orange-red with as-prepared paper containing DPPDC due to the acid-base interaction. The obvious emitting color change of DPPDC can be used as a visual sensor to detect acid gas.
2016, 74(11): 902-909
doi: 10.6023/A16080452
Abstract:
The optical spectra are effective means to reveal the molecular interactions and the luminescent mechanism of the organic molecules in aggregates. Herein, we systematically investigate the crystalline state vibrationally resolved absorption and emission spectra for a series of AIEgens and non-AIEgens by considering intermolecular excited state interaction by using Frenkel-exciton model coupled with quantum mechanics and molecular mechanics (QM/MM) calculations. It is found that the competition between the intramolecular vibronic coupling (λ) and the intermolecular exciton coupling (J) governs the crystalline aggregate spectral characters. At room temperature, when J/λ value is larger than a critical value (ca. 0.17), the exciton coupling would have a large effect on the optical spectra. For face-to-face H-aggregates, only when both intermolecular electrostatic and excitonic couplings are considered, can one obtain calculated vibrationally resolved spectra and well reproduce the experimental results, namely, remarkable blue-shift in absorption but much less red-shift in emission when compared with the gas-phase. The optical spectra of the AIE-active aggregates are determined by the intramolecular vibronic coupling because the ratio J/λ is less than the critical value.
The optical spectra are effective means to reveal the molecular interactions and the luminescent mechanism of the organic molecules in aggregates. Herein, we systematically investigate the crystalline state vibrationally resolved absorption and emission spectra for a series of AIEgens and non-AIEgens by considering intermolecular excited state interaction by using Frenkel-exciton model coupled with quantum mechanics and molecular mechanics (QM/MM) calculations. It is found that the competition between the intramolecular vibronic coupling (λ) and the intermolecular exciton coupling (J) governs the crystalline aggregate spectral characters. At room temperature, when J/λ value is larger than a critical value (ca. 0.17), the exciton coupling would have a large effect on the optical spectra. For face-to-face H-aggregates, only when both intermolecular electrostatic and excitonic couplings are considered, can one obtain calculated vibrationally resolved spectra and well reproduce the experimental results, namely, remarkable blue-shift in absorption but much less red-shift in emission when compared with the gas-phase. The optical spectra of the AIE-active aggregates are determined by the intramolecular vibronic coupling because the ratio J/λ is less than the critical value.
