The charge distribution, molecular structure, and morphological packing significantly affect the photophysical properties of organic photoluminescent materials. In this work, two triphenylpyrrole isomers, 1,2,5- (TPP1) and 1,3,4- (TPP2), were first synthesized and characterized. Because of their different substituent positions, TPP1 possesses aggregation-caused emission quenching (ACQ) behavior while TPP2 exhibits aggregation-induced emission (AIE). Their different photoluminescent properties were systematically investigated by using UV–vis absorption spectroscopy, fluorescence spectroscopy, density functional theory (DFT) calculations, and single-crystal structure analysis. The results indicate that substituent position of the two phenyl groups predominately affects the charge distribution of the isomers and determines their molecular packing structures, which further cause the different restriction of intramolecular rotation (RIR) capabilities of phenyl rings, thus resulting in different luminescence properties of these two triphenylpyrrole isomers under different aggregate states.

•A novel pyrrolopyrrole derivative DPPCN exhibited aggregation- and crystalline-induced emission properties.•DPPCN showed three types of polymorphism with blue, cyan-blue and yellow-green emissive, respectively.•The structure-property relationships were investigated based on X-ray single crystal diffraction analysis.•The mechano- and thermo-stimulus fluorescence switching behaviors of the three crystals were investigated.Bis(4-cyanophenyl)-4,4′-(2,5-diphenylpyrrolo[3,2-b] pyrrole-1,-4-diyl) dibenzoate (DPPCN) was synthesized and exhibited aggregation-induced emission properties. DPPCN was cultivated in different solvents getting three kinds of crystals, A, B and C. Crystals of A and B were respectively blue and cyan-blue emissive, while C was yellow-green emissive. They all displayed crystalline-induced emission behaviors. According to X-ray single crystal diffraction analysis, the intermolecular interactions account for restricted internal rotations, leading to fluorescence enhancement. The different kinds of co-effects of the solvent, intermolecular forces, molecular conformations and molecular packing modes endow DPPCN polymorphisms with multi-color emissions (from blue to yellow and up to 60 nm) and different fluorescence efficiencies. The fluorescence of A can be reversibly tuned by grinding and exposing to chloroform vapor with a 46 nm wavelength change. The crystal of C can blue shifted the fluorescence that matches with B upon fumed by chloroform for about 12 h and further blue shifted the fluorescence emission that matches with A when fumed by chloroform for about 24 h. Multi-color fluorescence tuning and switching is attributed to the nature of polymorphs, that is, a change of molecular conformation and intermolecular packing modes. The crystal of A also exhibited thermo-stimulus fluorescence switching behavior due to the co-crystallization with solvent chloroform. The properties of A show promising applications in temperature monitoring and volatile organic compound detecting devices.Download high-res image (283KB)Download full-size image

•The compound 1,2,4,5-tetraphenyl-1,4-dihydropyrrolo[3,2-b]pyrrole (DPPTP) exhibits aggregation-induced emission enhancement (AEE) and crystalline-induced emission enhancement (CEE) properties.•The DPPTP films show rapid response, excellent selectivity, and sensitivity to chloroform vapor.•The DPPTP solid films have good reversibility and also can be used as a quantitative analysis sensor for the detection of chloroform at as low as 100 ppm level.An one-step synthesized 1,2,4,5-tetraphenyl-1,4-dihydropyrrolo [3,2-b]pyrrole (DPPTP) exhibits aggregation-induced emission enhancement properties. The solid film prepared by spin-coating a DPPTP solution in THF onto a quartz glass showed rapid response and excellent selectivity to chloroform when fumed with different organic solvents. Experimental results show that hydrochloric gas produced from the photodecomposition of chloroform is the main reason for the fluorescent response of the DPPTP film to chloroform. The DPPTP solid films have good reversibility and also can be used as a quantitative analysis sensor for the detection of chloroform as low as 100 ppm.An one-step synthesized 1,2,4,5-tetraphenyl-1,4-dihydropyrrolo [3,2-b]pyrrole (DPPTP) exhibits aggregation-induced emission enhancement properties. The solid film prepared by spin-coating a DPPTP solution in THF onto a quartz glass showed rapid response and excellent selectivity to chloroform when fumed with different organic solvents. Experimental results show that hydrochloric gas produced from the photodecomposition of chloroform is the main reason for the fluorescent response of the DPPTP film to chloroform. The DPPTP solid films have good reversibility and also can be used as a quantitative analysis sensor for the detection of chloroform as low as 100 ppm.

A novel fluorescent probe, tris (2-(dimethylamino) ethyl)-4,4′,4″-(1H-pyrrole-1,2,5-triyl) tribenzoate (TPP-TMAE), with aggregation-enhanced emission (AEE) feature showed a simple, highly selective, specific, and instant response to trace amount carbon dioxide (CO2). Because of this special characteristic, TPP-TMAE is ideal to be a biomarker for in-situ monitoring of the CO2 generation rate during the metabolism of single living cell. The rates in single living HeLa cell, MCF-7 cell, and MEF cell were 6.40 × 10−6 ± 6.0 × 10−8 μg/h, 5.78 × 10−6 ± 6.0 × 10−8 μg/h, and 4.27 × 10−7 ± 4.0 × 10−9 μg/h, respectively. The distinct responses of TPP-TMAE to CO2 generated from cancer cells and normal cells suggested TPP-TMAE as a useful tool for deeper understanding metabolism process and distinguishing cancer cells from normal cells during the early diagnosis of cancers.

Novel fluorescent probes based on the 1,2,5-triphenylpyrrole core containing a different number of tertiary amine moieties, 2-(dimethylamino)ethyl 4-(2,5-diphenyl-1H-pyrrol-1-yl)benzoate (TPP-DMAE), bis(2-(dimethylamino)ethyl) 4,4′-(1-phenyl-1H-pyrrole-2,5-diyl)dibenzoate (TPP-BDMAE) and tris(2-(dimethylamino)ethyl) 4,4′,4′′-(1H-pyrrole-1,2,5-triyl)tribenzoate (TPP-TDMAE), with an aggregation-enhanced emission (AEE) feature, were prepared for the quantitative detection of low levels of carbon dioxide in the gas mixture with the fraction of carbon dioxide ranging from 0.4% to 5%. Compared with the other two compounds, TPP-TDMAE showed the most selective, fastest and most iterative response to carbon dioxide. A significant fluorescence decrease with a turn-off ratio over 20-fold was triggered by the disaggregation process through the reaction with carbon dioxide. Response time results indicated that the emission intensity of TPP-TDMAE can be quickly decreased to the minimum level in less than 12 s upon bubbling of carbon dioxide. It is desirable to develop a novel method for the selective, real-time and quantitative detection of CO2 for biological and medical applications.

In this work, we report the synthesis and photophysical studies of a new luminogen, A3MN, a diaminomaleonitrile-functionalized Schiff base. A3MN is aggregation-enhanced emission (AEE)-active: the emission of A3MN is enhanced with the aggregate formation. A3MN also possesses twisted intramolecular charge transfer (TICT) properties, showing noticeable solvatofluorochromism. Interestingly, the crystals of A3MN are nonemissive; the defect areas of the crystal, however, are highly emissive, as confirmed by spectroscopic methods and confocal microscopy. By taking advantage of this defect sensitive feature, a “turn-on” type of mechanofluorochromic material is developed, the emission of which is significantly enhanced under pressure or shear force. The detection limit reaches 0.1 Newton owing to its “turn-on” nature. Such defect-induced emission also renders A3MN sensitive to various kinds of mechanical actions, including hitting, friction, sculpture, and ultrasonic vibration.

Fully conjugated metallosupramolecular self-assembled multilayer films were controllably fabricated based on bibenzonitril-phthalocyaninato ruthenium(II) (BBPR) and 4,4′-bipyridine (BP) via axially coordination interaction between ruthenium ions and the pyridine groups on the modified substrates. The substrates were first functionalized by 4-(pyridine-4-ylethynyl)benzenic diazonium salt (PBD) through photodecomposition of diazonium group under UV irradiation. As a result, the pyridine-containing functional groups were vertically and covalently anchored onto the surface of substrate and got a stable monolayer. Soluble ruthenium phthalocyanine, axially coordinated by labile benzonitrile groups, was used to fabricate the layer-by-layer self-assembled films with BP through ligand-exchanging reaction between benzonitrile and pyridine in each self-assembled cycle. The UV–vis analysis results demonstrated the successful fabrication of bi(4,4′-bipyridine)phthalocyaninato ruthenium(II) (BPPR) metallosupramolecular ultrathin films with definite structures on PBD-modified substrate. Under illumination, the BPPR self-assembled multilayer films displayed a quick response to light. The maximum current density reached 120 nA/cm2 at six bilayers. The Eg, HOMO, and LUMO of the six-bilayer were quantitatively measured to be 1.68, −5.29, and −3.61 eV, respectively. This strategy supplies a facile method to get full-conjugated metallosupramolecules and a platform for developing higher performance solar cell from the point of adjusting dye aggregate state structure.

A “turn-on” fluorescent sensor, sodium 4,4′,4′′-(1H-pyrrole-1,2,5-triyl)tri-benzoate (Py(PhCOO-Na)3), has been prepared for the detection of Al3+ in aqueous solution. The detection mechanism, as well the mechanism specific to Al3+, was studied by fluorescence spectroscopy, UV-vis spectroscopy and dynamic light scattering (DLS) measurement. Py(PhCOONa)3 exhibited an aggregation-induced emission (AIE) characteristic and was found to show a specific affinity to Al3+, as indicated by the enhanced and bathochromically shifted emission of the AIE fluorogen. Upon binding Al3+, a significant fluorescence enhancement with a turn-on ratio of over 10-fold was triggered by the AIE process. Moreover, this sensor is highly selective for Al3+ over other metal ions with a detection limit of 5 μM and a quantitative detection range of 5–120 μM, and is able to be used in the determination of Al3+ in drinking water. The time-response investigation indicates that the emission intensity of (Py(PhCOO−)3) can be quickly boosted to reach the maximum intensity in less than 10 s upon titration of Al3+.

A water-soluble, ‘turn-on’ fluorescent chemosensor based on aggregation-induced emission (AIE) has been developed. It exhibits rapid response, excellent selectivity, and sensitivity to Al3+.

An aggregation-induced emission (AIE)-active chromophore 1,2-bis[4-(3-hydroxyphenyl)phenyl]-1,2-diphenylethene (TPE-2PhOH) was synthesized from 1,2-bis[4-bromophenyl]-1,2-diphenylethene (TPE-2Br) and 3-hydroxylphenylboronic acid via Suzuki coupling reaction. TPE-2PhOH nanoaggregates can be obtained from the nonsolvent-induced aggregation process. By alternately depositing 4,4′-biphenyldiazonium (BPD) salts and TPE-2PhOH nanoaggregates, layer-by-layer self-assembled films based on hydrogen-bonding interactions were successfully fabricated onto modified quartz slides. A more stable film was further prepared by subsequent decomposition of diazonium group (–N2+) under irradiation of UV light, which induces the conversation of the hydrogen-bond interaction between the hydroxyl groups on the surface of TPE-2PhOH nanoaggregates and diazonium groups into covalent bonds. The covalently linked self-assembled film exhibited highly fluorescence quenching sensitivity towards volatile of solid nitroanilines (2-nitroaniline (2-NA), 3-nitroaniline (3-NA) and 4-nitroaniline (4-NA)) and 2,4,6-trinitrotoluene (TNT) at normal atmospheric temperature and pressure. This strategy can provide a platform for developing highly sensitive and efficient chemosensors for harmful compounds and warfare explosives.

4-(2-(4-pyridinyl)Ethynyl)benzenic diazonium salt (PBD) was used to modify multiwalled carbon nanotubes (MWCNTs) by the self-assembly technique. After the decomposition of the diazonium group in PBD under UV irradiation, the PBD monolayer film covalently anchored on multiwalled carbon nanotubes is very stable. The obtained pyridine-modified MWCNTs (Py(Ar)-MWCNTs) have good solubility in common organic solvents. Furthermore, the layer-by-layer (LBL) self-assembled fully conjugated films of Py(Ar)-MWCNTs and (phthalocyaninato)ruthenium(II) (RuPc) were fabricated on the PBD-modified substrates, and characterized using UV−vis absorption spectroscopy, scanning electron microscopy (SEM), and electrochemistry. The UV−vis analysis results indicate that the LBL RuPc/Py(Ar)-MWCNTs self-assembled multilayer films with axial ligands between the ruthenium atom and pyridine group were successfully fabricated, and the progressive assembly runs regularly with almost equal amounts of deposition in each cycle. A top view SEM image shows a random and homogeneous distribution of Py(Ar)-MWCNTs over the PBD-modified silicon substrate, which indicates well independence between all Py(Ar)-MWCNTs. Moreover, the opto-electronic conversion was also studied by assembling RuPc/Py(Ar)-MWCNTs multilayer films on PBD-modified ITO substrate. Under illumination, the LBL self-assembled films on ITO showed an effective photoinduced charge transfer because of their conjugated structure and the ITO current density changed with the number of bilayer. As the number of bilayers was increased, the photocurrent increases and reaches its maximum value (∼300 nA/cm2) at nine bilayers. These results allow us to design novel materials for applications in optoelectronic devices by using LBL self-assembly techniques.

The relationship between the structures and light emission properties of five aryl-substituted pyrrole derivatives was studied during aggregation in THF−water mixtures. Only pentaphenylpyrrole clearly shows, however, an aggregation-induced emission enhancement (AIEE) phenomenon. On comparison of the optical properties and single-crystal structures of these pyrrole derivatives, it is suggested that the more twisted configuration which prevented parallel orientation of conjugated chromophores combined with the restricted intramolecular rotation (RIR) effect was the main cause of the AIEE phenomenon.

An aggregation-induced emission (AIE)-active chromophore 1,2-bis[4-(3-hydroxyphenyl)phenyl]-1,2-diphenylethene (TPE-2PhOH) was synthesized from 1,2-bis[4-bromophenyl]-1,2-diphenylethene (TPE-2Br) and 3-hydroxylphenylboronic acid via Suzuki coupling reaction. TPE-2PhOH nanoaggregates can be obtained from the nonsolvent-induced aggregation process. By alternately depositing 4,4′-biphenyldiazonium (BPD) salts and TPE-2PhOH nanoaggregates, layer-by-layer self-assembled films based on hydrogen-bonding interactions were successfully fabricated onto modified quartz slides. A more stable film was further prepared by subsequent decomposition of diazonium group (–N2+) under irradiation of UV light, which induces the conversation of the hydrogen-bond interaction between the hydroxyl groups on the surface of TPE-2PhOH nanoaggregates and diazonium groups into covalent bonds. The covalently linked self-assembled film exhibited highly fluorescence quenching sensitivity towards volatile of solid nitroanilines (2-nitroaniline (2-NA), 3-nitroaniline (3-NA) and 4-nitroaniline (4-NA)) and 2,4,6-trinitrotoluene (TNT) at normal atmospheric temperature and pressure. This strategy can provide a platform for developing highly sensitive and efficient chemosensors for harmful compounds and warfare explosives.

A “turn-on” fluorescent sensor, sodium 4,4′,4′′-(1H-pyrrole-1,2,5-triyl)tri-benzoate (Py(PhCOO-Na)3), has been prepared for the detection of Al3+ in aqueous solution. The detection mechanism, as well the mechanism specific to Al3+, was studied by fluorescence spectroscopy, UV-vis spectroscopy and dynamic light scattering (DLS) measurement. Py(PhCOONa)3 exhibited an aggregation-induced emission (AIE) characteristic and was found to show a specific affinity to Al3+, as indicated by the enhanced and bathochromically shifted emission of the AIE fluorogen. Upon binding Al3+, a significant fluorescence enhancement with a turn-on ratio of over 10-fold was triggered by the AIE process. Moreover, this sensor is highly selective for Al3+ over other metal ions with a detection limit of 5 μM and a quantitative detection range of 5–120 μM, and is able to be used in the determination of Al3+ in drinking water. The time-response investigation indicates that the emission intensity of (Py(PhCOO−)3) can be quickly boosted to reach the maximum intensity in less than 10 s upon titration of Al3+.

A water-soluble, ‘turn-on’ fluorescent chemosensor based on aggregation-induced emission (AIE) has been developed. It exhibits rapid response, excellent selectivity, and sensitivity to Al3+.

In this work, we report the synthesis and photophysical studies of a new luminogen, A3MN, a diaminomaleonitrile-functionalized Schiff base. A3MN is aggregation-enhanced emission (AEE)-active: the emission of A3MN is enhanced with the aggregate formation. A3MN also possesses twisted intramolecular charge transfer (TICT) properties, showing noticeable solvatofluorochromism. Interestingly, the crystals of A3MN are nonemissive; the defect areas of the crystal, however, are highly emissive, as confirmed by spectroscopic methods and confocal microscopy. By taking advantage of this defect sensitive feature, a “turn-on” type of mechanofluorochromic material is developed, the emission of which is significantly enhanced under pressure or shear force. The detection limit reaches 0.1 Newton owing to its “turn-on” nature. Such defect-induced emission also renders A3MN sensitive to various kinds of mechanical actions, including hitting, friction, sculpture, and ultrasonic vibration.

Novel fluorescent probes based on the 1,2,5-triphenylpyrrole core containing a different number of tertiary amine moieties, 2-(dimethylamino)ethyl 4-(2,5-diphenyl-1H-pyrrol-1-yl)benzoate (TPP-DMAE), bis(2-(dimethylamino)ethyl) 4,4′-(1-phenyl-1H-pyrrole-2,5-diyl)dibenzoate (TPP-BDMAE) and tris(2-(dimethylamino)ethyl) 4,4′,4′′-(1H-pyrrole-1,2,5-triyl)tribenzoate (TPP-TDMAE), with an aggregation-enhanced emission (AEE) feature, were prepared for the quantitative detection of low levels of carbon dioxide in the gas mixture with the fraction of carbon dioxide ranging from 0.4% to 5%. Compared with the other two compounds, TPP-TDMAE showed the most selective, fastest and most iterative response to carbon dioxide. A significant fluorescence decrease with a turn-off ratio over 20-fold was triggered by the disaggregation process through the reaction with carbon dioxide. Response time results indicated that the emission intensity of TPP-TDMAE can be quickly decreased to the minimum level in less than 12 s upon bubbling of carbon dioxide. It is desirable to develop a novel method for the selective, real-time and quantitative detection of CO2 for biological and medical applications.