A Vibration-Induced Emission-Based Ratiometric Sensor for Detection of Anions in Aqueous Solution

Sensors that respond to anions via vibration-induced emission (VIE) have recently emerged as effective tools for discrimination between closely related carboxylate species in non-competitive, organic solvents. However, the utility of this sensing mechanism has not yet been demonstrated for anions in aqueous media. Here, we prepared two sensors, monoZnDPA-DPAC and ZnDPA-DPAC, with either one or two anion-binding motifs. These systems are capable of binding to anions in water. Dual emission via VIE is maintained in solvent mixtures of up to 70% water. ZnDPA-DPAC provides a unique, ratiometric response to citrate and phosphate, which was used for the accurate quantification of aqueous solutions of these anions.

A rapid screening method for thermal conductivity properties of thermal insulation materials by a thermochemiluminescence probe

Acridine-based 1,2-dioxetane as a thermochemiluminescence (TCL) probe for temperature sensing exhibited an excellent response for temperature in the range of 85-130 °C with favorable sensitivity and good resolution. The proposed TCL probe could be applied to screen thermal conductivity properties of different thermal insulation materials.

The endeavor of vibration-induced emission (VIE) for dynamic emissions

Organic chromophores with large Stokes shifts and dual emissions are fascinating because of their fundamental and applied interest. Vibration-induced emission (VIE) refers to a tunable multiple fluorescence exhibited by saddle-shaped N,N'-disubstituted-dihydribenzo[a,c]phenazines (DHPs), which involves photo-induced configuration vibrations from bent to planar form along the N-N axis. VIE-active molecules show intrinsic long-wavelength emissions in the unconstrained state (planar state) but bright short-wavelength emissions in the constrained state (bent state). The emission response for VIE-active luminogens is highly sensitive to steric hindrance encountered during the planarization process such that a tiny structural variation can induce an evident change in fluorescence. This can often be achieved by tuning the intensity ratio of short- and long-wavelength bands. In some special cases, the alterations in the emission wavelength of VIE fluorophores can be achieved step by step by harnessing the degree of bending angle motion in the excited state. In this perspective, we summarize the latest progress in the field of VIE research. New bent heterocyclic structures, as novel types of VIE molecules, are being developed, and the general features of the chemical structures are also being proposed. Technologically, novel emission color-tuning approaches and VIE-based probes for visualizing biological activity are presented to demonstrate how the dynamic VIE effect can be exploited for cutting-edge applications.

Internal standard fluorogenic probe based on vibration-induced emission for visualizing PTP1B in living cells

Herein, as a proof of concept, we developed the first enzymatic VIE fluorogenic probe for protein tyrosine phosphatase 1B (PTP1B).

Measuring the Microphase Separation Scale of Polyurethanes with a Vibration-Induced Emission-Based Ratiometric "Fluorescent Ruler"

Polyurethanes (PUs) are a very attractive type of segmented polymer with unique mechanical properties derived from thermodynamic incompatibility between flexible soft segments and hard segments. The performance of PUs is closely related to their microphase separation structures, in which the hard domains serve as physical cross-linking points in the soft matrix. Studying the microphase separation of PUs in a facile manner is thus of great significance but challenging due to the complexity of the internal structures of PUs. N,N'-disubstituted-dihydrophenazine (DPAC) derivatives, the typical molecules featured with vibration-induced emission (VIE) attribute, can emit fluorescence varying with surrounding environment. In this proof-of-concept work, a series of DPAC derivatives were employed as built-in ratiometric "fluorescent rulers" to measure the degree of microphase separation in PUs modulated by temperature variation. The fluorescence of selected DPAC-doped PU films is dependent on the temperature, providing a theoretical basis for this concept. The feasibility of these fluorescent rulers was further validated by the small-angle X-ray scattering (SAXS) analysis. The SAXS curves show significant change in q range of 0.02 to 0.15 Å^-1 with the variation in temperature, showing the changes in the internal microstructure. The polydisperse hard sphere model analysis of the scattering data revealed that the volume fraction of hard spheres has a defined relationship with the fluorescence intensity ratio of orange-red light and blue light, thereby demonstrating a novel fluorimetry method for measuring and monitoring the microphase separation of polyurethanes.

Ratiometric Indicator Based on Vibration-Induced Emission for in Situ and Real-Time Monitoring of Gelation Processes

Monitoring specific processes such as gelation in a ratiometric and visual manner is of scientific value and has practical implications but remains challenging. Herein, an innovative fluorescent low-molecular-weight gelator (DPAC-CHOL) capable of revealing and self-revealing the gelation processes in situ and in real time via the ratiometric fluorescence change from orange-red to blue has been developed. By virtue of its vibration-induced emission attribute, the gelation point, critical gelation concentration, and the internal stiffness of the gel networks of DPAC-CHOL and other gelation systems could be facilely evaluated in a ratiometric and naked-eye-observable fashion. Noteworthily, the DPAC-CHOL-doped gelation system Ph-CHOL can quantitatively identify the environmental temperature in a daily-concerned range (i.e., 20-55 °C). This work not only provides a versatile advanced material but also opens up a new avenue for the investigation of gelation systems.

Compression of a Flapping Mechanophore Accompanied by Thermal Void Collapse in a Crystalline Phase

Mechanical control of the molecular energy landscape is an important issue in modern materials science. Mechanophores play a unique role in that the mechanical responses are induced against the activation barrier for intramolecular transformation with the aid of external forces. Here we report an unprecedented activation process of a flexible flapping mechanophore. Namely, thermal void collapse in a crystalline phase triggers mechanophore compression in a definite proportion. Unfavored conformational planarization of the flapping mechanophore is compulsorily induced by packing force, leading to a total energy gain in crystal packing. Fluorescence chromism indicates extended π conjugation resulting from the mechanophore compression, giving rise to an energy transfer from the unpressed to compressed conformers.

Conformational Planarization versus Singlet Fission: Distinct Excited-State Dynamics of Cyclooctatetraene-Fused Acene Dimers

A set of flapping acene dimers fused with an 8π cyclooctatetraene (COT) ring showed distinct excited-state dynamics in solution. While the anthracene dimer showed a fast V-shaped-to-planar conformational change within 10 ps in the lowest excited singlet state, reminding us of extended Baird aromaticity, the tetracene dimer and the pentacene dimer underwent intramolecular singlet fission (SF) in different manners: A fast and reversible SF with a characteristic delayed fluorescence (FL), and a fast and quantitative SF, respectively. Conformational flexibility of the fused COT linkage plays an important role in these ultrafast dynamics, demonstrating the utility of the flapping molecular series as a versatile platform for designing photofunctional systems.

T and V-shaped donor–acceptor–donor molecules involving pyridoquinoxaline: large Stokes shift, environment-sensitive tunable emission and temperature-induced fluorochromism

The critical role of molecular shapes in the environment-sensitive and temperature-induced emission properties of pyridoquinoxaline-based donor–acceptor–donor molecules was demonstrated.

Phenazine-Based Ratiometric Hg2+ Probes with Well-Resolved Dual Emissions: A New Sensing Mechanism by Vibration-Induced Emission (VIE)

Phenazines exhibit intriguing vibration-induced emission (VIE) owing to the fast intrinsic vibration of benzo[a,c]phenazine moiety. For the first time, a phenazine-based ratiometric fluorescent probe DBPST is developed for recognizing Hg²⁺ via restriction of VIE. Upon binding with Hg²⁺ , DBPST demonstrates two well-resolved emission peaks (over 130 nm) with a wide tuning color and affords a large signal-to-background ratio.