Restriction Of Intramolecular Vibration Research Articles

Aggregation induced emission dynamic chiral europium(III) complexes with excellent circularly polarized luminescence and smart sensors

The synthesis of dynamic chiral lanthanide complex emitters has always been difficult. Herein, we report three pairs of dynamic chiral EuIII complex emitters (R/S-Eu-R-1, R = Et/Me; R/S-Eu-Et-2) with aggregation-induced emission. In the molecular state, these EuIII complexes have almost no obvious emission, while in the aggregate state, they greatly enhance the EuIII emission through restriction of intramolecular rotation and restriction of intramolecular vibration. The asymmetry factor and the circularly polarized luminescence brightness are as high as 0.64 (5D0 → 7F1) and 2429 M−1cm−1 of R-Eu-Et-1, achieving a rare double improvement. R-Eu-Et-1/2 exhibit excellent sensing properties for low concentrations of CuII ions, and their detection limits are as low as 2.55 and 4.44 nM, respectively. Dynamic EuIII complexes are constructed by using chiral ligands with rotor structures or vibration units, an approach that opens a door for the construction of dynamic chiral luminescent materials.

Effect of bulky side groups on photophysical properties and electroluminescent performance of oligo(styryl)benzenes

The rational design of electroluminescent compounds has been recognized as a promising strategy to maximize the efficiency of electronic devices. In this work, we analyze the impact of the substitution of n-alkyl and n-alkoxy side chains by bulkier side groups (tert-butyl and tert-butoxy) on the photophysics of the two model fluorophores 1,3,5-tris(styryl)benzene and 1,2,4,5-tetra(styryl)benzene. We found that the bulky side groups have a significant contribution to the vibrational normal modes associated with the non-radiative deactivation. The aggregation-induced enhanced emission phenomenon observed in some cases was attributed to the blocking of the trans→cis photoisomerization and the restriction of intramolecular vibrations. In the solid state, the bulky side groups have demonstrated to play a determining role in the supramolecular structure and photophysical properties, particularly in the case of the tetra(styryl)benzenes. In light-emitting devices, we found that the incorporation of the bulky side groups in oligo(styryl)benzenes could reduce the electromer formation and improve the device performance. The tetra(styryl)benzenes, and particularly the tert-butyl derivative, showed better device performance, with lower turn-on voltage, higher current density and electroluminescent intensity.

Synthesis and AIE properties of benzene fused cyclooctetrathiophenes

We have synthesized a series of benzene fused cyclooctetrathiophenes (COThs), including BCOTh, 2BCOTh, 3BCOTh, and 4BCOTh with rotor-free molecular structures, which are similar to the luminogens with the aggregation-induced emission (AIE) property based on the mechanism of restriction of intramolecular vibration (RIV). Investigation on the photophysical properties in THF-H2O mixture solvent showed that 4BCOTh exhibits the aggregation-caused quenching (ACQ) properties, while the others exhibit AIE effect. With increasing the number of the fused benzene rings, the emission behaviors of COThs showed hypsochromic shift in both rigid solution (77 K) and AIE state, which are attributed to the gradually weakened intramolecular through-space conjugation (ITSC). Theoretical calculations and crystal packing analysis indicated that the emission difference in solid between 2BCOTh and 4BCOTh is mainly affected by the factors of molecular conjugation and rigidity. In addition, the model compound COThMe, bearing two methylene groups locking the thiophene rings of COTh, was employed for the experimental investigation of RIV mechanism in the AIE case of COThs.

Multiple stimuli-responsive properties of Coumarin-Salicylaldehyde Schiff Bases

Organic small-molecules of multiple stimuli-responses were widely paid attention, which can be applied in multiple fields simultaneously, such as thermal sensor, force response, pH probe, reagents for the detection of metal ion and so forth. In the present work, three novel coumarin derivatives (XDS-R) were synthesized from various salicylaldehydes containing different substituents (R = H, Cl, Br), following by investigations about their multiple stimuli-responsive properties concerning aggregation-induced emission (AIE), mechanochromism, thermochromism and pH response. Single crystals of XDS-R indicate that intramolecular hydrogen bonds cause the restriction of intramolecular vibration, leading to AIE character and mechanochromic property. Interestingly, two substituents (H, Cl) have little effect on fluorescence intensity and color, and whereas have distinguishable influences on functionalized fluorescence response. In the pH range of 2.00–8.00, only XDS-H exhibited regular pH-response, while XDS-Cl and XDS-Br showed excellent pH tolerance. Mechanochromic XDS-R is able to recover to original state under heating. A simple multilevel anticounterfeit label was made by the combination of XDS-Cl and previous-reported DDHAC without an automatic heat-inspired recovery. Combined multilevel stimuli-responsive material of XDS-Cl and previous DDHAC displayed potential application of anti-counterfeiting mark.

Supramolecular cuboctahedra with aggregation-induced emission enhancement and external binding ability.

Beyond the AIE (aggregation-induced emission) phenomenon in small molecules, supramolecules with AIE properties have evolved in the AIE family and accelerated the growth of supramolecular application diversity. Inspired by its mechanism, particularly the RIV (restriction of intramolecular vibrations) process, a feasible strategy of constructing an AIE-supramolecular cage based on the oxidation of sulfur atoms and coordination of metals is presented. In contrast to previous strategies that used molecular stacking to limit molecular vibrations, we achieved the desired goal using the synergistic effects of coordination-driven self-assembly and oxidation. Upon assembling with zinc ions, S1 was endowed with a distinct AIE property compared with its ligand L1, while S2 exhibited a remarkable fluorescence enhancement compared to L2. Also, the single cage-sized nanowire structure of supramolecules was obtained via directional electrostatic interactions with multiple anions and rigid-shaped cationic cages. Moreover, the adducts of zinc porphyrin and supramolecules were investigated and characterized by 2D DOSY, ESI-MS, TWIM-MS, UV-vis, and fluorescence spectroscopy. The protocol described here enriches the ongoing research on tunable fluorescence materials and paves the way towards constructing stimuli-responsive luminescent supramolecular cages.

Aggregation-Induced Fluorogens in Bio-Detection, Tumor Imaging, and Therapy: A Review

Aggregation-Induced Fluorogens in Bio-Detection, Tumor Imaging, and Therapy: A Review

Restriction of Intramolecular Vibration in Aggregation‐Induced Emission Luminogens: Applications in Multifunctional Luminescent Metal–Organic Frameworks

AbstractButterfly‐like molecules of oxacalix[2]arene[2]pyrazine (OAP) are reported, which exhibit the typical characteristics of aggregation‐induced emission (AIE) via the restriction of intramolecular vibration (RIV) mechanism. Unlike any of the reported RIV‐type AIE molecules, the synthetic procedures of which are complicated and have associated high costs, OAP AIEgens can be synthesized in a facile manner by a one‐step catalyst‐free reaction using commercially available materials. Notably, OAP AIEgens are ideal ligands for constructing metal–organic frameworks (MOFs) due to their built‐in pyrazine coordination sites. OAP‐based MOFs exhibit multiple potential applications in reversible gas response, encrypted information storage, and construction of white light‐emitting devices. This work builds on RIV‐type AIEgens, offers additional selections of bridging ligands for constructing luminescent MOFs and provides a visualized prototype to understand the effect of the RIV process on the luminescence properties of MOFs.

Restriction of Intramolecular Vibration in Aggregation-Induced Emission Luminogens: Applications in Multifunctional Luminescent Metal-Organic Frameworks.

Butterfly-like molecules of oxacalix[2]arene[2]pyrazine (OAP) are reported, which exhibit the typical characteristics of aggregation-induced emission (AIE) via the restriction of intramolecular vibration (RIV) mechanism. Unlike any of the reported RIV-type AIE molecules, the synthetic procedures of which are complicated and have associated high costs, OAP AIEgens can be synthesized in a facile manner by a one-step catalyst-free reaction using commercially available materials. Notably, OAP AIEgens are ideal ligands for constructing metal-organic frameworks (MOFs) due to their built-in pyrazine coordination sites. OAP-based MOFs exhibit multiple potential applications in reversible gas response, encrypted information storage, and construction of white light-emitting devices. This work builds on RIV-type AIEgens, offers additional selections of bridging ligands for constructing luminescent MOFs and provides a visualized prototype to understand the effect of the RIV process on the luminescence properties of MOFs.

Understanding the Driving Mechanisms of Enhanced Luminescence Emission of Oligo(styryl)benzenes and Tri(styryl)-s-triazine.

This work is focused on unraveling the mechanisms responsible for the aggregation-induced enhanced emission and solid-state luminescence enhancement effects observed in star-shaped molecules based on 1,3,5-tris(styryl)benzene and tri(styryl)-s-triazine cores. To achieve this, the photophysical properties of this set of molecules were analyzed in three states: free molecules, molecular aggregates in solution, and the solid state. Different spectroscopy and microscopy experiments and DFT calculations were conducted to scrutinize the causative mechanisms of the luminescence enhancement phenomenon observed in some experimental conditions. Enhanced luminescence emission was interpreted in the context of short- and long-range excitonic coupling mechanisms and the restriction of intramolecular vibrations. Additionally, we found that the formation of π-stacking aggregates could block E/Z photoisomerization through torsional motions between phenylene rings in the excited state, and hence, enhancing the luminescence of the system.

Unraveling Dual Aggregation-Induced Emission Behavior in Steric-Hindrance Photochromic System for Super Resolution Imaging.

Unprecedented dual aggregation-induced emission (AIE) behavior based on a steric-hindrance photochromic system is presented, with incorporation one or two bulky aryl groups, resulting in different flexibleness. The dual AIE behavior of open and closed isomers can be explained by restriction of intramolecular rotation (RIR), restriction of intramolecular vibration (RIV), and intermolecular stacking. The large bulky benzothiophene causes restricted rotation, enhancing the emission of open form in solution and weak π-π molecular packing, thereby efficiently enhancing the luminescence performance in the solid state. With incorporation of two large bulky benzothiophene groups, BBTE possesses the most outstanding AIE activity, undergoing highly efficient and reversible off-to-on fluorescence in film upon alternating UV and visible light irradiation along with excellent fatigue resistance. The off-to-on fluorescent photoswitch is successfully established in super resolution imaging.

Unraveling Dual Aggregation‐Induced Emission Behavior in Steric‐Hindrance Photochromic System for Super Resolution Imaging

AbstractUnprecedented dual aggregation‐induced emission (AIE) behavior based on a steric‐hindrance photochromic system is presented, with incorporation one or two bulky aryl groups, resulting in different flexibleness. The dual AIE behavior of open and closed isomers can be explained by restriction of intramolecular rotation (RIR), restriction of intramolecular vibration (RIV), and intermolecular stacking. The large bulky benzothiophene causes restricted rotation, enhancing the emission of open form in solution and weak π–π molecular packing, thereby efficiently enhancing the luminescence performance in the solid state. With incorporation of two large bulky benzothiophene groups, BBTE possesses the most outstanding AIE activity, undergoing highly efficient and reversible off‐to‐on fluorescence in film upon alternating UV and visible light irradiation along with excellent fatigue resistance. The off‐to‐on fluorescent photoswitch is successfully established in super resolution imaging.

Recent Advances in the Z/E Isomers of Tetraphenylethene Derivatives: Stereoselective Synthesis, AIE Mechanism, Photophysical Properties, and Application as Chemical Probes.

Focused research on the Z/E isomers of tetraphenylethene (TPE) derivatives is scarce in comparison with the thousands of luminogens with AIE properties (AIEgens) that have been synthesized based on the TPE moiety. The similar chemical and physical properties of the Z/E isomers make them difficult to separate by using conventional chromatographic techniques. However, they can be isolated by introducing polar groups and the pure isomers exhibit very different photophysical properties, mechanochromism, and host-guest coordination, as well as assisting in deciphering the AIE mechanism. In this Minireview, we present an overview of the disagreement regarding the AIE mechanism between the restriction of intramolecular vibration and photoinduced Z/E isomerization. Then, we discuss the development of (Z)-/(E)-TPE derivatives, their use in host-guest detection, and their mechanoluminescence properties, with a focus on their photophysical characteristics. Finally, we explore the stereoselective synthesis of pure (Z)-/(E)-TPE derivatives.

A Nonarchetypal 5,6-Dihydro-2H-pyrano[3,2-g]indolizine-Based Solution-Solid Dual Emissive AIEgen with Multicolor Tunability.

Screening of a chemical library of pyranones and their ring transformed fluorophores led to the discovery of a novel 5,6-dihydro-2H-pyrano[3,2-g]indolizine (DPI) class of the luminogen DPI 7, which exhibited unique solution-solid dual emission (SSDE) behavior with an emission color shift from bright-green in solution to a strong red emission in the solid state. The AIE mechanism of these luminogens revealed a well-defined set of noncovalent interactions (CH⋅⋅⋅O and CH⋅⋅⋅N) that block the motion of C2 -flexure leading to restriction of intramolecular vibrations (RIV) in the solid state. DPI-7 is the first example of solution-solid dual emissive RIV-based AIEgen, which has great potential both in biomedical imaging and optoelectronic fields.

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).