Junge Zhi

Aggregation-Induced Emission Enhancement of Aryl-Substituted Pyrrole Derivatives

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.

A highly sensitive, single selective, real-time and “turn-on” fluorescent sensor for Al3+ detection in aqueous media

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+.

Crystallization-Induced Emission Enhancement in a Phosphorus-Containing Heterocyclic Luminogen

Whereas aggregation often quenches luminescence, the emission of a heterocyclic luminogen, 10-[2,5-bis(4-pentyloxyphenylcarbonyloxy)phenyl]-9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (3), is greatly enhanced by aggregate formation. Crystallization further boosts the emission of 3, turning it from a weak emitter in the solution state to a strong emitter in the crystalline state. The emission of 3 is changed in response to the exposure to vapors of volatile organic compounds (VOCs). The morphology of the thin film of 3 is reversibly and repeatedly modulated between amorphous and crystalline phases by simple fuming-heating and heating-cooling cycles, leading to an emission switching between bright and dark states. The novel attributes of the crystallization-induced emission enhancement, the VOC-responsive emission change, and the morphology-tunable emission switching of 3 could enable it to find applications in an array of technological areas, including chemosensing, optical display, and rewritable information storage.

Mechanochromic Behavior of Aryl-Substituted Buta-1,3-Diene Derivatives with Aggregation Enhanced Emission

Three tetra-aryl substituted 1,3-butadiene derivatives with aggregation enhanced emission (AEE) and mechanochromic fluorescence behavior have been rationally designed and synthesized. The results suggest an effective design strategy for developing diverse materials with aggregation induced emission (AIE) and significant mechanochromic performance by employing D-π-A structures with large dipole moments.

Fabrication and optoelectronic properties of novel films based on functionalized multiwalled carbon nanotubes and (phthalocyaninato)ruthenium(II) via coordination bonded layer-by-layer self-assembly.

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/cm(2)) at nine bilayers. These results allow us to design novel materials for applications in optoelectronic devices by using LBL self-assembly techniques.

Aggregation-induced emission enhancement in poly(phenylene-ethynylene)s bearing aniline groups

Poly(phenylene ethynylene)s (P1) with 4-vinylaniline pendant groups were successfully prepared by the Sonogashira coupling polymerization between 1,4-diethynyl-2,5-bis(pentyloxy)benzene and 4-[2-(2,5-dibromophenyl)vinyl]-aniline. In comparison with its analogue P2 without amino group, the emission of P1 is only enhanced by aggregation when adding n-hexane into its THF solution, exhibiting an aggregation-induced emission enhancement (AIEE) effect. When methanol or water instead of hexane was added into THF solution, P1, however, didn’t show AIEE. The results indicated that amino groups strengthen the inter-chain and intra-chain interactions in P1 and restrict the non-radiative energy transition. This strategy can provide a platform for developing highly sensitive and efficient bio- and chemosensors.

An AIEE polyelectrolyte as a light-up fluorescent probe for heparin sensing in full detection range

Polyelectrolyte PTPEPyH, containing tetraphenylethene (TPE) and pyridinium, was synthesized. Its optical properties were investigated with spectroscopies and the results showed that there were two emission-enhanced stages in the interaction between positive-charged PTPEPyH and negative-charged biomacromolecule heparin. The mechanism was very different due to the reduced non-radiative energy loss and the change of surroundings. The polyelectrolyte PTPEPyH, compared with ChS and HA, also showed high selectivity for heparin in the buffer solution and could be used as a potential bio-probe for heparin quantification in the clinical full range.

The synthesis of chiral triphenylpyrrole derivatives and their aggregation-induced emission enhancement, aggregation-induced circular dichroism and helical self-assembly

A pair of enantiomers ((R)-TPPBAm and (S)-TPPBAm) and their raceme (rac-TPPBAm) were designed and prepared by conjugating (R)-, (S)- or racemic 1-phenylethylamine to an aggregation-induced emission enhancement (AIEE) active triphenylpyrrole fluorophore. The three target compounds were thoroughly characterized and their optical properties were systematically investigated. The fluorescence analyses indicate that they all retain the AIEE activities originating from the triphenylpyrrole moiety, irrespective of the attaching groups. More importantly, both the enantiomers containing (R)- or (S)-1-phenylethylamine attachment exhibit aggregation-induced circular dichroism (AICD) features with mirror-image signals. Besides, they also exhibit circularly polarized luminescence (CPL) with an emission dissymmetry factor (gem) from 1.5 × 10−4 to 3 × 10−3 for (R)-TPPBAm and −1.3 × 10−4 to −4 × 10−3 for (S)-TPPBAm in aggregate states. As expected, consistent with the variations of their CD signals, (R)-TPPBAm and (S)-TPPBAm could self-assemble into helical nanofibers with the opposite screw direction during the aggregation process in the THF–water mixed solution, while the racemic compound rac-TPPBAm exhibits no CD and CPL signals, and self-assembles to form nanoparticles blocks. These results demonstrate that the morphologies and optical activities can be controlled simultaneously without losing the solid-state emission performance of the material by attaching a chiral group to an AIEE fluorophore, which could shed light on the design of optical active fluorophores for sensitive and time-efficient enantiomer determination.

Aggregation-induced emission enhancement and aggregation-induced circular dichroism of chiral pentaphenylpyrrole derivatives and their helical self-assembly

Herein, a pair of enantiomers, (S)-PPPtriAm and (R)-PPPtriAm, with three chiral substituents and their raceme rac-PPPtriAm derived from conjugated luminogen pentaphenylpyrrole were prepared by covalently attaching (R)-/(S)- or racemic 1-phenylethylamine to conjugated 1-biphenyl-2,3,4,5-tetraphenyl pyrrole. The compounds exhibit obvious aggregation-induced emission enhancement (AIEE) features, and the chiral substituents have little effect on the photophysical properties. More importantly, the introduction of chiral substituents endows the chiral compounds (S)-PPPtriAm and (R)-PPPtriAm with distinct aggregation-induced circular dichroism (AICD) with mirror-image Cotton effects and chiral-polarized luminescence (CPL) properties with an emission dissymmetry factor (gem) in the range of 0.5 × 10−3 to 5 × 10−3 for (S)-PPPtriAm and −1 × 10−3 to −6 × 10−3 for (R)-PPPtriAm in a DMSO–water mixture with the water fraction of 40%. The chiral compounds (S)-PPPtriAm and (R)-PPPtriAm can self-assemble into nanofibers, and the lank nanofibers orderly weave and align together to form a regular arrangement of aggregates. The raceme rac-PPPtriAm exhibits AIEE features without any AICD and CPL signals and can self-assemble to form nanoparticle blocks. The enantiomers (S)-PPPtriAm and (R)-PPPtriAm, as AIEE-active luminogens with a multichiral substituent, are expected to have potential applications in photoelectronic materials or in the design of optically active fluorophores for sensitive enantiomer recognition.

The Synergistic Effect between Triphenylpyrrole Isomers as Donors, Linking Groups and Acceptors on the Fluorescence Properties of D-π-A Compounds in the Solid State

Eight donor-π-acceptor (D-π-A) compounds employing triphenylpyrrole isomers (TPP-1,2,5 and TPP-1,3,4) as donors, malononitrile (CN) and 1H-indene-1,3(2H)-dione (CO) as acceptors, pyridone (P) and benzopyran (B) as π-linking groups were synthesized. The compounds exhibited aggregation-induced emission and piezochromic properties. Compared with previously reported donors, triphenylpyrroles induced all the compounds to have more remarkable photophysical properties. The compounds containing TPP-1,2,5 and P moieties displayed stronger fluorescence intensities, shorter emission wavelengths, and more distinct piezochromic properties. However, the same phenomenon was observed in the TPP-1,3,4-containing system if B was as π-linker. Moreover, the CN acceptor endowed the compound to have a relatively strong fluorescent intensity, in which CO induced a relatively long emission wavelength. That is, the photophysical properties of D-π-A compounds can be controlled by adjusting the structure of donor, linker and acceptor.