Vibration-induced Emission Research Articles

Tunable Nano-Bending Structures of Loosened/Tightened Lassos with Bi-Stable Vibration-Induced Emissions for Multi-Manipulations of White-Light Emissions and Sensor Applications.

The first tunable nano-bending structures of [1]rotaxane containing a single-fluorophoric N,N'-diphenyl-dihydrodibenzo[a,c]phenazine (DPAC) moiety (i.e., [1]RA) are developed as a loosened lasso structure to feature the bright white-light emission [CIE (0.27, 0.33), Φ = 21.2%] in THF solution, where bi-stable states of bending and twisted structures of DPAC unit in [1]RA produce cyan and orange emissions at 480 and 600nm, respectively. With acid/base controls, tunable loosened/tightened nano-loops of corresponding [1]rotaxanes (i.e., [1]RA/[1]RB) can be achieved via the shuttling of macrocycles reversibly, and thus to adjust their respective white-light/cyan emissions, where the cyan emission of [1]RB is obtained due to the largest conformational constraint of DPAC moiety in its bending form of [1]RB with a tightened lasso structure. Additionally, the non-interlocked analog M-Boc only shows the orange emission, revealing the twisted form of DPAC fluorophore in M-Boc without any conformational constraint. Moreover, the utilization of solvents (with different viscosities and polarities), temperatures, and water fractions could serve as effective tools to adjust the bi-stable vibration-induced emission (VIE) colors of [1]rotaxanes. Finally, tuning ratiometric emission colors of adaptive conformations of DPAC moieties by altering nano-bending structures in [1]rotaxanes and external stimuli can be further developed as intelligent temperature and viscosity sensor materials.

Multimode Stimuli-Responsive Room-Temperature Phosphorescence Achieved by Doping Butterfly-like Fluorogens into Crystalline Small-Molecular Hosts.

Materials with stimuli-responsive purely organic room-temperature phosphorescence (RTP) exempt from exquisite molecular design and complex preparation are highly desirable but still relatively rare. Moreover, most of them work in a single switching mode. Herein, we employ a versatile host-guest-doped strategy to facilely construct efficient RTP systems with multimode stimuli-responsiveness without ingenious molecular design. By conveniently doping butterfly-like guests, namely, N,N'-diphenyl-dihydrodibenzo[a,c]phenazines (DPACs), featured with vibration-induced emission into the small-molecular hosts via various methods, RTP systems with finely tunable photophysical properties are readily obtained. Through systematic mechanistic studies and with the aid of a series of control experiments, we unveil the critical role of the host crystallinity in achieving efficient RTP. By virtue of the inherent environmental sensitivity of both RTP and fluorescence of the DPACs, our systems exhibit multiple-stimuli-responsiveness with the luminescence not only switching between the fluorescence and phosphorescence but also continuously changing in the fluorescence color. Advanced dynamic anticounterfeiting and multilevel information encryption is thereby realized.

Dual Stimuli-Responsive [2]Rotaxanes with Tunable Vibration-Induced Emission and Switchable Circularly Polarized Luminescence.

Aiming at the construction of novel stimuli-responsive fluorescent system with precisely tunable emissions, the typical 9,14-diphenyl-9,14-dihydrodibenzo[a, c]phenazine (DPAC) luminogen with attractive vibration-induced emission (VIE) behavior has been introduced into [2]rotaxane as a stopper. Taking advantage of their unique dual stimuli-responsiveness towards solvent and anion, the resultant [2]rotaxanes reveal both tunable VIE and switchable circularly polarized luminescence (CPL). Attributed to the formation of mechanical bonds, DPAC-functionalized [2]rotaxanes display interesting VIE behaviors including white-light emission upon the addition of viscous solvent, as evaluated in detail by femtosecond transient absorption (TA) spectra. In addition, ascribed to the regulation of chirality information transmission through anion-induced motions of chiral wheel, the resolved chiral [2]rotaxanes reveal unique switchable CPL upon the addition of anion, leading to significant increase in the dissymmetry factors (glum ) values with excellent reversibility. Interestingly, upon doping the chiral [2]rotaxanes in stretchable polymer, the blend films reveal remarkable emission change from white light to light blue with significant 6.5-fold increase in glum values up to -0.035 under external tensile stresses. This work provides not only a new design strategy for developing molecular systems with fluorescent tunability but also a novel platform for the construction of smart chiral luminescent materials for practical use.

Dual Stimuli‐Responsive [2]Rotaxanes with Tunable Vibration‐Induced Emission and Switchable Circularly Polarized Luminescence

AbstractAiming at the construction of novel stimuli‐responsive fluorescent system with precisely tunable emissions, the typical 9,14‐diphenyl‐9,14‐dihydrodibenzo[a, c]phenazine (DPAC) luminogen with attractive vibration‐induced emission (VIE) behavior has been introduced into [2]rotaxane as a stopper. Taking advantage of their unique dual stimuli‐responsiveness towards solvent and anion, the resultant [2]rotaxanes reveal both tunable VIE and switchable circularly polarized luminescence (CPL). Attributed to the formation of mechanical bonds, DPAC‐functionalized [2]rotaxanes display interesting VIE behaviors including white‐light emission upon the addition of viscous solvent, as evaluated in detail by femtosecond transient absorption (TA) spectra. In addition, ascribed to the regulation of chirality information transmission through anion‐induced motions of chiral wheel, the resolved chiral [2]rotaxanes reveal unique switchable CPL upon the addition of anion, leading to significant increase in the dissymmetry factors (glum) values with excellent reversibility. Interestingly, upon doping the chiral [2]rotaxanes in stretchable polymer, the blend films reveal remarkable emission change from white light to light blue with significant 6.5‐fold increase in glum values up to −0.035 under external tensile stresses. This work provides not only a new design strategy for developing molecular systems with fluorescent tunability but also a novel platform for the construction of smart chiral luminescent materials for practical use.

Tuning vibration-induced emission through macrocyclization and catenation.

In order to investigate the effect of macrocyclization and catenation on the regulation of vibration-induced emission (VIE), the typical VIE luminogen 9,14-diphenyl-9,14-dihydrodibenzo[a, c]phenazine (DPAC) was introduced into the skeleton of a macrocycle and corresponding [2]catenane to evaluate their dynamic relaxation processes. As investigated in detail by femtosecond transient absorption (TA) spectra, the resultant VIE systems revealed precisely tunable emissions upon changing the solvent viscosity, highlighting the key effect of the formation of [2]catenane. Notably, the introduction of an additional pillar[5]arene macrocycle featuring unique planar chirality endows the resultant chiral VIE-active [2]catenane with attractive circularly polarized luminescence in different states. This work not only develops a new strategy for the design of new luminescent systems with tunable vibration induced emission, but also provides a promising platform for the construction of smart chiral luminescent materials for practical applications.

Phenotyping of Methicillin-Resistant Staphylococcus aureus Using a Ratiometric Sensor Array.

Chemical tools capable of classifying multidrug-resistant bacteria (superbugs) can facilitate early-stage disease diagnosis and help guide precision therapy. Here, we report a sensor array that permits the facile phenotyping of methicillin-resistant Staphylococcus aureus (MRSA), a clinically common superbug. The array consists of a panel of eight separate ratiometric fluorescent probes that provide characteristic vibration-induced emission (VIE) profiles. These probes bear a pair of quaternary ammonium salts in different substitution positions around a known VIEgen core. The differences in the substituents result in varying interactions with the negatively charged cell walls of bacteria. This, in turn, dictates the molecular conformation of the probes and affects their blue-to-red fluorescence intensity ratios (ratiometric changes). Within the sensor array, the differences in the ratiometric changes for the probes result in "fingerprints" for MRSA of different genotypes. This allows them to be identified using principal component analysis (PCA) without the need for cell lysis and nucleic acid isolation. The results obtained with the present sensor array agree well with those obtained using polymerase chain reaction (PCR) analysis.

Transparent–Flexible–Moldable Low-Temperature Thermometer Constructed by Harnessing Vibration-Induced Emission of Dihydrophenazine in Polydimethylsiloxane

Transparent–Flexible–Moldable Low-Temperature Thermometer Constructed by Harnessing Vibration-Induced Emission of Dihydrophenazine in Polydimethylsiloxane

A carbon dioxide responsive fluorescent system based on micellar transformation

Carbon dioxide (CO2) responsive fluorescent systems mainly focus on modification of fluorophores with specific CO2-responsive groups, the processes of which are usually tedious and time-consuming. Here, we report a facile strategy for fabricating CO2-responsive fluorescent system by employing a surfactant, N,N-Dimethyl-1- dodecanamine (C12A), to form an oil-in-water (O/W) emulsion and a fluorophore with vibration-induced emission, which could be solubilized in the oil core. At the presence of CO2, the tertiary amine groups of C12A were protonated due to the reaction between C12A and carbonic acid, resulting in a transition of the semitransparent emulsion mixture to a transparent micellar solution due to the increased amphipathicity of C12A. Correspondingly, the micro-environment of the fluorophores in the oil core had been changed, leading to an obvious emission color variation from bright pink to blue. Thus, these responsive behaviors were visible to the naked eyes and could be simultaneously monitored by fluorescence and transmittance measurements. Repeatability and cyclability of this system were easily achieved by bubbling nitrogen (N2) into this system or heating, demonstrating great potential application of this system for CO2 detection. As a concept-of-proposal, the CO2-responsive system was proved to be effective in monitoring respiration during the process of seed germination.

New insight into mechanochromic property of one N,N′-disubstituted-dihydrodibenzo[a‚c]phenazine derivative

We report herein the reversible mechanochromic luminescence property of (dibenzo[a,c]phenazine-9,14-diylbis(4,1-phenylene))dimethanol (DPAC-OH) where the photoluminescene color changes from blue to blue-green upon grinding, which can be restored upon slow solvent evaporation. 9,14-bis(4-(methoxymethyl)phenyl)-9,14-dihydrodibenzo[a,c]phenazine (DPAC-OCH3) is synthesized as the control sample to further demonstrate the role of hydrogen bonding in DPAC-OH. The vibration-induced emission (VIE) mechanism and the presence of hydrogen bonding interactions are utilized to account for the mechanochromic phenomenon.

Probing vibronic coupling of a transiently charged state of a single molecule through subnanometer resolved electroluminescence imaging

The intramolecular vibronic coupling has a great effect on molecular electronic transitions and associated spectral characteristics, which is a central topic in the study of molecular spectroscopy. In this paper, we investigate the vibronic coupling of a transiently charged state within a single 3,4,9,10-perylenetetracarboxylicdianhydride (PTCDA) molecule in real space by imaging the spatial distribution of single-molecule electroluminescence via highly localized excitation of tunneling electrons in a plasmonic nanocavity. The electron injections from a scanning tunneling microscope tip into a PTCDA molecule on a silver-supported ultrathin salt layer produce a transient doubly charged molecular anion that emits vibrationally resolved fluorescence. The sub-molecular resolved spectroscopic imaging for the –2 valence transiently charged state shows a two-spot pattern along the molecular short axis for the purely electronic 0-0 transition. However, the observed two-spot orientation for certain anti-symmetric vibronic-state imaging is found to be evidently different from the purely electronic 0-0 transition, rotating 90°, which reflects the change in the transition dipole orientation from along the molecular short axis to the long axis. Such a change directly reveals the occurrence of strong vibronic coupling associated with a large Herzberg-Teller (HT) contribution, which goes beyond the conventional Franck-Condon (FC) picture. Combined with theoretical calculations, the anti-symmetric vibration is found to have a strong dynamic disturbance to the transition density of purely electronic transitions, especially those atoms with large transition densities, which induces a strong transition charge oscillation along the long axis of the molecule and thus leads to a transition dipole along the long axis of the molecule. On the other hand, for vibronic emissions associated with the totally symmetric molecular vibration (such as the v<sub>1</sub> (A<sub>g</sub>) mode described above), the observed two-spot orientation in the vibronic-state imaging pattern is found to be the same as the purely electronic 0-0 transition, which directly reveals its FC-dominated nature. Notably, the vibration-induced emission associated with HT-dominated contributions (such as the v<sub>2</sub> (B<sub>3g</sub>) mode) is often discussed in the literature by using an intensity borrowing mechanism via the state mixing with other high-lying eigenstates. In the present work, the v<sub>2</sub>-vibration with B<sub>3g</sub> symmetry is likely to modulate the zero-order electronic wavefunction of the S<sub>1</sub> state in a way to best resemble that of the S<sub>2</sub> state (<i>i.e.</i>, induce efficient mixing of the electronic excited state S<sub>1</sub> with the electronic excited state S<sub>2</sub>), so that the v<sub>2</sub>-vibration induced emission seems to borrow intensities from neighboring S<sub>2</sub>→S<sub>0</sub> transitions. Our results provide a new route for the real-space understanding of the microscopic picture for the vibronic coupling within a single molecule in a transiently charged state.

Vibratile Dihydrophenazines with Controllable Luminescence Enabled by Precise Regulation of π-Conjugated Wings

Vibratile Dihydrophenazines with Controllable Luminescence Enabled by Precise Regulation of π-Conjugated Wings

A Vibration-Induced-Emission-Based Fluorescent Chemosensor for the Selective and Visual Recognition of Glucose.

The development of chemosensors to detect analytes in biologically relevant solutions is a challenging task. We report the synthesis of a fluorescent receptor that combines vibration‐induced emission (VIE) and dynamic covalent chemistry for the detection of glucose in aqueous media. We show that the bis‐2‐(N‐methylaminomethyl)phenylboronic acid‐decorated N,N′‐diphenyl‐dihydrodibenzo[a,c]phenazine (DPAC) receptor 1 can detect glucose and discriminate between closely related monosaccharides including those commonly found in blood. Preliminary studies suggest monosaccharides bind to the DPAC‐receptor with a 1:1 stoichiometry to produce pseudomacrocyclic complexes, which in turn leads to distinct optical changes in the fluorescent emission of the receptor for each host. Moreover, the complexation‐induced change in emission can be detected visually and quantified in a ratiometric way. Our results highlight the potential of VIE‐type receptors for the quantitative determination of saccharides in biological samples.

A Vibration‐Induced‐Emission‐Based Fluorescent Chemosensor for the Selective and Visual Recognition of Glucose

AbstractThe development of chemosensors to detect analytes in biologically relevant solutions is a challenging task. We report the synthesis of a fluorescent receptor that combines vibration‐induced emission (VIE) and dynamic covalent chemistry for the detection of glucose in aqueous media. We show that the bis‐2‐(N‐methylaminomethyl)phenylboronic acid‐decorated N,N′‐diphenyl‐dihydrodibenzo[a,c]phenazine (DPAC) receptor 1 can detect glucose and discriminate between closely related monosaccharides including those commonly found in blood. Preliminary studies suggest monosaccharides bind to the DPAC‐receptor with a 1:1 stoichiometry to produce pseudomacrocyclic complexes, which in turn leads to distinct optical changes in the fluorescent emission of the receptor for each host. Moreover, the complexation‐induced change in emission can be detected visually and quantified in a ratiometric way. Our results highlight the potential of VIE‐type receptors for the quantitative determination of saccharides in biological samples.

Confinement fluorescence effect (CFE): Lighting up life by enhancing the absorbed photon energy utilization efficiency of fluorophores

The absorption photon energy utilization efficiency of small molecule fluorophores can be enhanced only through the conformational change of a single molecule (without destruction/aggregation/assembly/packing). Therefore, the so-called confinement fluorescence effect (CFE) can be used as an used as a useful sensing strategy for bio-sensing/imaging probes to light up life without a change in molecule structure. So far, many scientists have carried out a great proportion of their work making use of this property of fluorescent molecules. In recent years, vibration-induced emission (VIE), dissociation-induced emission (DIE), rigidification-induced emission, changes in motion-induced change in emission (MICE), assembling-induced emission, molecular binding set identification characteristics (MUSIC), especially the term used for the generation of emission by aggregation (aggregation-induced emission, AIE), have contributed to a better understanding of fluorescence sensing mechanisms. However, as a universal concept, the CFE has not been systematically summarized. Herein, we focus on describing the concepts and characteristics of CFEs, demonstrate their various applications, present unique advantages of CFE-based organic small molecule fluorophores, and discuss the technical challenges encountered in this area of research. We hope that the review will promote a deeper comprehension of CFEs, enable the construction of strategies for various luminescent materials, and facilitate the development of advanced fluorescent functional materials.

Donor-conformation-dependent energy transfer for dual-color fluorescent probe with high-resolution imaging

Herein, we presented a brand-new concept to construct the Forster resonance energy transfer (FRET) based cassette by integrating a vibration-induced emission (VIE) chromophore as the donor. Different from traditional donors only with a single emission, the VIE donor possessed well-separated dual emission bands by altering the excited state molecular configuration from bent state to the planar state. By linking an acceptor such as a cyanine dye (Cy5), a novel VIE-FRET cassette (PPCy5) was prepared. The planar emission profile of VIE donor moiety could fully cover the absorption of Cy5, thus the complete FRET process enabled the excellent bimodal spectra difference of 142 nm and ultra-large pseudo-Stokes shift of up to 300 nm. Benefiting from the viscosity-dependent characteristic of the VIE donor, PPCy5 could clearly and intuitively reveal the different viscosity regions in vivo by dual-color and high-resolution imaging. The VIE-FRET paradigm provides an optional platform for developing donor-acceptor based dual-color fluorescent probes with high-resolution imaging ability.

Light‐Responsive Circularly Polarized Luminescence Polymers with INHIBIT Logic Function

AbstractDynamically tuning the emission of circularly polarized luminescence (CPL) materials through external stimuli is fascinating because of their fundamental and application interests. In this work, light‐responsive and luminescence‐tunable CPL‐active materials are synthesized by mixing achiral helical polymer containing vibration‐induced emission (VIE) molecules and spiropyran (SP) with a chiral helical polymer. Through regulating the distinct emission of VIE molecules and the reversible photoisomerization of SP, the dynamic Förster resonance energy transfer (FRET) can be explored to reversibly control the emission color of CPL in different states after light‐controlled isomerization. This project is the first comprehensive investigation of CPL‐active materials with VIE properties. Finally, taking the advantage of the multistimuli responsive CPL signal in different states, an “INHIBIT” logic gate with CPL signal output based on the combination of control of UV/vis light irradiation time and state alternation is constructed.

Temperature-responsive molecular liquids based on dihydrophenazines for dynamic multicolor-fluorescent anti-counterfeiting and encryption

Multicolor printing, dynamic anti-counterfeiting, and advanced information encryption are conveniently realized by harnessing the temperature-sensitive and dual-emissive molecular liquids based on vibration-induced emission fluorogens.

Real-Time Visual Monitoring of Kinetically Controlled Self-Assembly.

The construction of artificial structures through hierarchical self-assembly based on noncovalent interactions, as well as monitoring during the self-assembly process, are important aspects of dynamic supramolecular chemistry. Herein we describe the complex dynamics of chiral N,N'-diphenyl dihydrodibenzo[a,c]phenazine derivatives (S)/(R)-DPAC, whose different assemblies were found to have distinct optical and morphological characteristics. With ratiometric fluorescence originating from vibration-induced emission (VIE), the self-assembly process from kinetic traps to the thermodynamic equilibrium state could be monitored in real time by optical spectrometry. During the morphology transformation from particles to nanobricks, strong circularly polarized luminescence was induced with glum =1.6×10-2 . The excited-state characteristics of the self-assemblies enabled investigation of the relationship between molecular aggregation and conformational change, thus allowing effective monitoring of the sophisticated supramolecular self-assembly process.

Real‐Time Visual Monitoring of Kinetically Controlled Self‐Assembly

AbstractThe construction of artificial structures through hierarchical self‐assembly based on noncovalent interactions, as well as monitoring during the self‐assembly process, are important aspects of dynamic supramolecular chemistry. Herein we describe the complex dynamics of chiral N,N′‐diphenyl dihydrodibenzo[a,c]phenazine derivatives (S)/(R)‐DPAC, whose different assemblies were found to have distinct optical and morphological characteristics. With ratiometric fluorescence originating from vibration‐induced emission (VIE), the self‐assembly process from kinetic traps to the thermodynamic equilibrium state could be monitored in real time by optical spectrometry. During the morphology transformation from particles to nanobricks, strong circularly polarized luminescence was induced with glum=1.6×10−2. The excited‐state characteristics of the self‐assemblies enabled investigation of the relationship between molecular aggregation and conformational change, thus allowing effective monitoring of the sophisticated supramolecular self‐assembly process.

Aqueous Systems with Tunable Fluorescence Including White-Light Emission for Anti-Counterfeiting Fluorescent Inks and Hydrogels.

White-light-emitting materials have attracted wide interest for potential applications in information displays and lighting. To date, the majority of reported white-light-emitting materials have been multicomponent systems that are typically processed with organic solvents. These features are associated with complex processing, poor white-light quality, and environmental pollution. Herein, a white-light-emitting aqueous system is realized by encapsulating a fluorophore, which has a vibration-induced emission effect, in Pluronic F127 micelles. Tunable multicolor fluorescence is achieved by changing the temperature, and the use of organic solvents is effectively avoided. Through this process, white-light emission with Commission Internationale de l'Eclairage coordinates of (0.3351, 0.3326) is obtained, which is very close to pure white light, and its color rendering index is as high as 89. The fluorescence color tunability of this system could be performed in a wide temperature range, rendering it a potential material in optical thermometry. Besides, the aqueous system also allows for the application of the material as a fluorescent ink and white-light-emitting hydrogels. Information could be embedded in paper-based materials and hydrogels through the fluorescence quenching effect of iron ions (Fe3+) on the fluorophore. Fluorescence could then be recovered upon removal of Fe3+ by adenosine 5'-triphosphate. Thus, fluorescent patterning and triple-mode anti-counterfeiting could be expected due to the temperature-sensitive emission, fluorescence quenching, and recovering properties.