Direct observation of intramolecular coplanarity regulated polymorph emission of a tetraphenylethene derivative

Polymorphism makes it possible to clarify the relationship between emission property and crystal structure. However, based on the exact molecular conformation in tetraphenylethene polymorphisms, it is still challenging to evaluate the difference of intramolecular coplanarity without the support of calculation because of the complex combination of four different torsion angles between four peripheral benzenes and the central ethylene plane. Here, by using a di-formyl-functionalized tetraphenylethene derivative, two ideal polymorphisms with a consistent trend of the corresponding torsion angles have been obtained. For the first time, we explicitly demonstrated that intramolecular coplanarity is the underlying cause of the polymorphism-dependent emission of tetraphenylethene derivatives.     

Coplanarity in the backbones of ladder-type oligo(p-phenylene) homologues and derivatives

p-Tolyl-substituted ladder-type oligo(p-phenylene)s containing three, four, and five phenylene rings were readily synthesized. The uniform aryl substitution of these systems allowed us to determine the coplanarity of the pi-conjugated backbones crystallographically. The intramolecular annulations eliminate almost all of the conformational disorder and enhance the degree of pi-conjugation of the backbones, resulting in significant red shifts in the absorption and emission maxima and lower oxidation potentials in the higher homologues. [structure: see text]     

Trackable Supramolecular Fusion: Cage to Cage Transformation of Tetraphenylethylene-Based Metalloassemblies

Herein, the trackable supramolecular transformation of a two-component molecular cage to a three-component cage through supramolecular fusion with another two-component molecular square is described. The use of tetraphenylethene (TPE), a chromophore with aggregation-induced emission (AIE) character, as a component for the molecular cages enables facile fluorescence monitoring of the transformation process: while both cages exhibit fluorescence emission via the restriction of intramolecular motion of the TPE motif, the interactions between TPE and 4,4′-bipyridine introduced in the supramolecular fusion process result in partial fluorescence quenching and shifts in the emission maximum. This study provides a simple and efficient approach towards complex supramolecular cages with emergent functions and demonstrates that AIE features could provide unique opportunities for the characterization of complex, dynamic supramolecular transformation processes.     

Trackable Supramolecular Fusion: Cage to Cage Transformation of Tetraphenylethylene‐Based Metalloassemblies

Herein, the trackable supramolecular transformation of a two‐component molecular cage to a three‐component cage through supramolecular fusion with another two‐component molecular square is described. The use of tetraphenylethene (TPE), a chromophore with aggregation‐induced emission (AIE) character, as a component for the molecular cages enables facile fluorescence monitoring of the transformation process: while both cages exhibit fluorescence emission via the restriction of intramolecular motion of the TPE motif, the interactions between TPE and 4,4′‐bipyridine introduced in the supramolecular fusion process result in partial fluorescence quenching and shifts in the emission maximum. This study provides a simple and efficient approach towards complex supramolecular cages with emergent functions and demonstrates that AIE features could provide unique opportunities for the characterization of complex, dynamic supramolecular transformation processes.     

Constructing a Nonfluorescent Conformation of AIEgen: A Tetraphenylethene Embedded in the Calix[4]arene's Skeleton

Two novel 1,1‐diphenylmethylidene decorated calix[4]arenes, ( Calix‐DPE(OCH₃)₄ and Calix‐DPE(OH)₄ ), were designed and prepared. The tetraphenylethene (TPE) unit is embedded in the calix[4]arenes skeleton, so the conformation of tetraphenylethene unit is significantly affected by the conformation of calix[4]arene. Unlike the Calix‐DPE(OCH₃)₄ , the Calix‐DPE(OH)₄ does not show the aggregation‐induced emission (AIE) phenomena in solution or the crystal state because of the presence of intramolecular hydrogen bonding, which leads to a cone conformation for the calix[4]arene skeleton in which the embedded phenyl rings of the TPE have to take an almost perpendicular configuration to the C=C bond. This result provides direct evidence that the maximal cross‐chromophore π‐conjugation within the tetraphenylethene is one of the prerequisites of switching on its AIE. This offers the possibility of switching the emission of TPE by conformation changes.     

Specific detection of D-glucose by a tetraphenylethene-based fluorescent sensor

A conceptually new "light-up" biosensor with a high specificity for d-glucose (Glu) in aqueous media has been developed. The emission from a tetraphenylethene (TPE)-cored diboronic acid (1) was greatly boosted when the fluorogen was oligomerized with Glu because of restriction of the intramolecular rotations of the aryl rotors of TPE by formation of the oligomer. Little change in the light emission was observed when 1 was mixed with D-fructose, D-galactose, or D-mannose, as these saccharides are unable to oligomerize with the fluorogen.     

Restriction of Intramolecular Motions: The General Mechanism behind Aggregation‐Induced Emission

Aggregation‐induced emission (AIE) has been harnessed in many systems through the principle of restriction of intramolecular rotations (RIR) based on mechanistic understanding from archetypal AIE molecules such as tetraphenylethene (TPE). However, as the family of AIE‐active molecules grows, the RIR model cannot fully explain some AIE phenomena. Here, we report a broadening of the AIE mechanism through analysis of 10,10′,11,11′‐tetrahydro‐5,5′‐bidibenzo[a,d][7]annulenylidene (THBDBA), and 5,5′‐bidibenzo[a,d][7]annulenylidene (BDBA). Analyses of the computational QM/MM model reveal that the novel mechanism behind the AIE of THBDBA and BDBA is the restriction of intramolecular vibration (RIV). A more generalized mechanistic understanding of AIE results by combining RIR and RIV into the principle of restriction of intramolecular motions (RIM).     

BSA-tetraphenylethene derivative conjugates with aggregation-induced emission properties: fluorescent probes for label-free and homogeneous detection of protease and α1-antitrypsin

Herein, BSA-tetraphenylethene derivative conjugates with aggregation-induced emission (AIE) properties were constructed and used as fluorescent probes for label-free detection of protease and α1-antitrypsin. Conjugated AIE probes were formed based on the electrostatic induced assembly between an ammonium cation of quaternized tetraphenylethene salt and carboxyl anion groups of BSA. While water soluble quaternized tetraphenylethene salt showed very low fluorescence in its well-dispersed state, obvious enhancement in the fluorescence of the aggregated tetraphenylethene derivative on the BSA templates was achieved due to the abnormal aggregation-induced emission properties of tetraphenylethene. These BSA-tetraphenylethene derivative conjugates enabled label-free detection of protease. In the presence of trypsin, the BSA templates were enzymatically hydrolyzed and the conjugates decomposed. Therefore the quaternized tetraphenylethene molecules became increasingly isolated from each other. Accordingly, the aggregation to dispersing state change of tetraphenylethene derivative resulted in an obvious decrease in the fluorescence of the conjugates probes and enabled the sensitive and selective detection of trypsin. Furthermore, upon addition of α1-antitrypsin, the enzymatic activity of trypsin was inhibited and the fluorescence was consequently preserved. Sensitive detection of α1-antitrypsin was thus realised. The protein-tetraphenylethene derivative conjugates with aggregation-induced emission properties therefore show great promise for the monitoring of biological processes and cancer diagnostics with simplicity, high sensitivity, and rapid response.     

Efficient enhancement of fluorescence emission via TPE functionalized cationic pillar[5]arene-based host–guest recognition-mediated supramolecular self-assembly

A tetraphenylethene (TPE) functionalized cationic pillar[5]arene (CWP5-TPE) was successfully synthesized, and the intramolecular rotation of the TPE motif was restricted via cationic pillar[5]arene-based host–guest recognition-mediated supramolecular self-assembly in water, resulting in the efficient enhancement of fluorescence emission based on the aggregation induced emission (AIE) mechanism. CWP5-TPE self-assembled into nanoribbons while the host–guest inclusion complex formed into supramolecular amphiphile nanoparticles in water.     

间位聚苯及其衍生物的构象与电子结构的理论研究

用分子力学方法(MM)对间位聚苯(PMP)及其衍生物的势能随扭曲角(f)变化规律进行了研究.结果表明，势能曲线上出现四个能量最小值，分别对应于扭曲角f ≈－135°,－45°,45°,135°.进一步对以上构建的全部PMP及其衍生物用分子力场Drieding 2.11进行了分子力学能量优化.最终得到主要的四种构象，其中螺旋构象的能量最低，而且以螺旋构象为优势分布构象.在真实条件下，PMP及其衍生物长链可能采取以上四种构象的混合片段组成.用量子化学方法(GGA-DFT)研究了PMP及其衍生物的电子结构能隙随相邻苯环之间的扭曲角的变化趋势.用量子化学半经验方法(AM1)对四种构象分别进行几何优化，优化结果与分子力学优化结果基本一致，并运用混合密度泛函方法(DFT/B3LYP/6-31G)进一步对AM1优化的构象结构进行更精确的电子结构能隙计算.最终得出影响间位聚苯及其衍生物电子结构能隙的主要因素为连接苯环间扭曲角的大小.     

Synthesis and Design of Aggregation‐Induced Emission Surfactants: Direct Observation of Micelle Transitions and Microemulsion Droplets

The direct visualization of micelle transitions is a long‐standing challenge owing to the intractable aggregation‐caused quenching of light emission in the micelle solution. Herein, we report the synthesis of a surfactant with a tetraphenylethene (TPE) core and aggregation‐induced emission (AIE) characteristics. The transition processes of surfactant micelles and the microemulsion droplets (MEDs) formed by the surfactant with a TPE core were clearly visualized by a high‐contrast fluorescence imaging method. The fluorescence intensity of the MEDs decreased as the size of MEDs increased as a result of weakening of the restriction of intramolecular rotation (RIR). The results of this study deepen our understanding of micelle‐transition processes and provide solid evidence in favor of the hypothesis that the AIE phenomenon has its origin in the RIR of fluorophores in the aggregate state.     

Self-Assembly and Fluorescence of Tetracationic Liquid Crystalline Tetraphenylethene

A series of tetraguanidinium tetraphenylethene (TPE) arylsulfonates with different chain lengths was prepared via ionic self-assembly of tetraguanidinium TPE chloride and the respective methyl arylsulfonates. Liquid crystalline properties were studied by differential scanning calorimetry, polarizing optical microscopy and X-ray diffraction. Tetraguanidinium TPE arylsulfonates with chain lengths of C₈–C₁₂ displayed hexagonal columnar mesophases over a broad temperature range, while derivatives with longer chains showed oblique columnar phases. In solution all compounds displayed aggregation-induced emission behaviour. Temperature-dependent luminescence spectra of the bulk phase of the tetraguanidinium TPE arylsulfonate with C₁₄ side chains revealed a strong luminescence both in the solid state and the oblique columnar mesophase. The emission behaviour was rationalized by a unique combination of restriction of intramolecular rotation of the TPE core, Coulomb interaction between the guanidinium cations and π–π interactions of the anionic arylsulfonate moieties.     

Anion‐Coordination‐Induced Turn‐On Fluorescence of an Oligourea‐Functionalized Tetraphenylethene in a Wide Concentration Range

A tetrakis(bisurea)‐decorated tetraphenylethene (TPE) ligand ( L² ) was designed, which, upon coordination with phosphate ions, displays fluorescence “turn‐on” over a wide concentration range, from dilute to concentrated solutions and to the solid state. The fluorescence enhancement can be attributed to the restriction of the intramolecular rotation of TPE by anion coordination. The crystal structure of the A₄L₂ (A=anion) complex of L² with monohydrogen phosphate provides direct evidence for the coordination mode of the anion. This “anion‐coordination‐induced emission” (ACIE) is another approach for fluorescence turn‐on in addition to aggregation‐induced emission (AIE).     

Photocontrolled Intramolecular Charge/Energy Transfer and Fluorescence Switching of Tetraphenylethene‐Dithienylethene‐Perylenemonoimide Triad with Donor–Bridge–Acceptor Structure

Photochromic 1,2‐dithienylethene (DTE) derivatives with a high thermal stability and fatigue resistance are appealing for optical switching of fluorescence. Here, we introduce a donor–photochromic bridge–acceptor tetraphenylethene‐dithienylethene‐perylenemonoimide (TPE‐DTE‐PMI) triad, in which TPE acts as the electron donor, PMI as the electron acceptor, and DTE as the photochromic bridge. In this system, the localized and intramolecular charge transfer emission of TPE‐DTE‐PMI with various Stokes shifts have been observed due to the photoinduced intramolecular charge transfer in different solvents. Upon UV irradiation, the fluorescence quenching resulting from photochromic fluorescence resonance energy transfer in TPE‐DTE‐PMI has been demonstrated in solution and in solid films. The fluorescence on/off switching ratio in polymethylacrylate film exceeds 100, a value much higher than in polymethylmethacrylate film, thus indicating that the fluorescence switching is dependent on matrices.     

Preparation of Functional Poly(aroyltriazole)s by Metal-Free Click Polymerization

Functional poly(aroyltriazoles) (PATAs) were synthesized by heating mixtures of bis(aroylacetylene)s and diazides in polar solvents such as DMF/toluene at a moderate temperature of 100 °C with high molecular weights (M_w up to 17 200) and regioregularities (1,4-regioisomeric ratio up to ∼95%) in high yields (up to ∼95%). The obtained polymers are soluble in common organic solvents and are thermally stable. The PATAs containing triphenylamine units emit visible light and show unique solvatochromism, exhibiting large two-photon absorption cross sections due to the intramolecular charge transfer between their electron-donating triphenylamine and electron-accepting aroyltriazole units. The tetraphenylethene (TPE)-functionalized polymer shows intriguing aggregation-induced emission phenomenon, that is, the polymer is weakly emissive in its solution state but emit strongly in its aggregate/solid state with quantum yield of ∼7.1%.     

Geometry optimization of molecular clusters and complexes using scaled internal coordinates

Scaled internal coordinates are introduced for use in the geometry optimization of systems composed of multiple fragments, such as solvated molecules, clusters, and biomolecular complexes. The new coordinates are related to bond lengths, bond angles and torsion angles by geometry-dependent scaling factors. The scaling factors serve to expedite the optimization of complexes containing outlying fragments, without hindering the optimization of the intramolecular degrees of freedom. Trial calculations indicate that, at asymptotic separations, the scaling factors improve the rate of convergence by a factor of 4 to 5.     

A tetraphenylethene based polarity dependent turn-on fluorescence strategy for selective and sensitive detection of Hg in aqueous medium and in living cells

A turn-on fluorescent chemosensor strategy based on the change in the polarity of aggregation induced emission active tetraphenylethene is presented for the detection of Hg²⁺ in aqueous medium and in living cells. The sensing mechanism involves the formation of nonpolar fluorescent aggregates of tetraphenylethene molecules by elimination of polar moieties of TPE with Hg²⁺ interaction.     

The Lagrange multiplier method for manipulating geometries. Implementation and applications in molecular mechanics

It is shown that a Lagrange multiplier method to constrain one or several internal coordinates, or averages and combinations of these, is easily implemented in a molecular mechanics computer program that uses Newton–Raphson (NR ) minimization. Results are given for constraints on nonbonded distances and torsion angles. When a potential energy surface is to be explored, it is much better to constrain the average of three torsion angles around a bond than to constrain a single torsion angle. Certain conversions can only be achieved when averages of torsion angles around different bonds are constrained. Combinations of constraints have been applied to evaluate differences between calculated and observed geometries and to obtain transition states for relatively large molecules from results for smaller molecules at relatively low costs. The efficieny of the combination of the Lagrange multiplier method and NR minimization in terms of computing time can be rated as good.     

Synthesis and characterization of cross‐shaped p–n diblock oligomers

The cross‐shaped p–n diblock oligomers based on oligothiophenes (OTs) and 1,3,4‐oxadiazole (OXD) were synthesized and investigated regarding optical properties, electrochemistry, quantum chemical calculations, and intramolecular energy transfer. Since only one emission peak is observed in PL spectra of the oligomers, it is evidenced that effective energy transfer from the OXD to OTs branch. The electrochemical experiments show that almost complete spatial separation of HOMO and LUMO with the thiophene number increasing. The theoretical calculations were carried out regarding which conformer is the lowest in energy, the torsion angle between thiophene/oxadiazole and the central benzene ring, and electron densities distributions of the oligomers. Based on all data, a model for intramolecular energy‐transfer process has been put forward to explain the optical properties. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1066–1073, 2007     

Magnetic interactions in p-phenylene-bis(nitronyl nitroxide) biradicals with large torsion angles

We have designed and synthesized new biradicals of p-phenylene-bis(nitronyl nitroxide) substituted with two methoxy groups at 2,3- (2) and 2,5-positions (3). A parent biradical p-phenylene-bis(nitronyl nitroxide) (1) has intramolecular antiferromagnetic exchange interaction of 2J/k_B = −104 K ∼ −106 K with a torsion angle of 28.5° between the phenyl and the imidazole rings of nitronyl nitroxide. X-ray crystal structure analysis shows that the bulky substituents in 2 and 3 give large torsion angles of 65–70°. The larger torsion angles should weaken the magnitude of intramolecular exchange interactions, which is attributed to a decrease in π-conjugation over the p-phenylene and the radical groups. Magnetic susceptibility measurements indicate that the intramolecular exchange interactions in 2 and 3 are severely weakened to about 6% of that in 1, 2J/k_B = −6 K ∼ −8 K. The relation between the torsion angle and the intramolecular exchange interaction is consistent with DFT calculations. The ground-state singlet biradicals with suppressed intramolecular exchange interactions can be a building block for exotic exchange-coupled spin systems as predicted in our theoretical studies.