An AIE-Active probe for detection and bioimaging of pH values based on lactone hydrolysis reaction

Aggregation-induced emission-based fluorescent probes for cellular microenvironment detection

The cellular microenvironment exerts a pivotal regulatory influence on cell survival, function, and behavior. Dynamic analysis and detection of the cellular microenvironment can promptly elucidate changes in cellular microenvironmental information, uncover the pathogenesis of diseases associated with aberrant microenvironments, and aid in predicting disease risk and monitoring disease progression. Aggregation-induced emission (AIE) fluorescent molecules possess unique AIE characteristics and offer significant advantages in imaging and sensing cellular microenvironments. In this review, we present a profile of the remarkable progress achieved in utilizing AIE fluorescent molecules for detecting cellular microenvironments in recent years. We particularly focus on AIE fluorescent probes applied in imaging key parameters of the cellular microenvironment, including pH, viscosity, polarity, and temperature, as well as in analyzing critical biological components of the microenvironment, such as gas signal molecules, metal ions, redox state, and proteins. We underscore the design principles, detection mechanisms, sensing performance, and biological applications of these fluorescent probes. Furthermore, we address the current challenges confronting this field and provide prospects for the future development of AIE probes used for microenvironment detection. We trust that this review will inspire researchers to develop more precise and sensitive AIE fluorescent probes for the detection of cellular microenvironments.

3-Aroylbenzocoumarin-Based Luminogens: Bright Solid-State Emission, AIE Properties and Cell Imaging Application

A series of 3-aroylbenzocoumarin-based luminogens have been synthesized for investigating their aggregation-induced emission (AIE) and solid-state fluorescence. The single crystal X-ray diffraction analysis of one of them showed that the molecules are arranged in the form of π-dimers which may lead to excimer emission. The large Stokes shifts and the broad-band emission of these 3-aroylbenzocoumarins in solid/aggregation state demonstrated the probable formation of excimers. The shapes of benzocoumarin units have a great effect on the AIE behaviors. The linear benzocoumarin derivatives show larger Stokes shifts, while the bent-benzocoumarin derivatives exhibit better AIE performances. All of them show aggregation-enhanced excimer emission which is supported by the large Stokes shifts. The electronic effect of 3-aroyl groups also has a certain effect on their fluorescence properties. The polymorphism phenomenon was observed for one of the benzoyl-containing derivatives. Additionally, two of the derivatives containing methoxy group were successfully used for cell imaging.

Non-trivial ground and excited state photophysics of a substituted phenol

5-(tert-Butyl)-2-hydroxy-1,3-isophthalaldehyde (5-tBHI) shows solvent dependent single or dual emission. The photophysics of 5-tBHI has been studied in a variety of solvents and the results were compared with that of the methyl derivative of the probe as well as the 5-tBHI anion. It has been found that the intramolecular H-bonded conformer of 5-tBHI predominantly exists in non-polar solvents, and undergoes facile excited state intramolecular proton transfer (ESIPT). On the other hand, a dynamic equilibrium can be found in polar, protic solvents, even in the ground state, except in water. NMR analyses confirm the loss of aromaticity of the probe in the ground state via anion formation, in equilibrium with the solvent mediated intermolecularly H-bonded state, in neat polar protic solvents like methanol. The proton transfer process, either intramolecularly or intermolecularly, was found to be of the order of 1 ps, and even faster than the instrumental resolution in the case of water. The current finding provides important insights on the photophysics of this small, substituted phenol.

Decomposition of Unpolarized Fluorescence Spectrum of Uniaxially Oriented 1,3,5-Triphenylbenzene Microcrystals Into Polarized Fluorescence Spectra

Luminescence from solids such as crystals and aggregates is of growing academic and industrial interest. In this study, we report decomposition of the unpolarized fluorescence spectrum of uniaxially oriented 1,3,5-triphenylbenzene (TPB) microcrystals into four polarized spectra measured with polarizer (V: vertical and H: horizontal) and analyser (V: vertical and H: horizontal), where V and H indicate perpendicular and parallel to the layer of TPB molecules in the crystal, respectively. Resolved spectra were interpreted in terms of the molecular and excimer like (J- and H-dimer) emissions. The origin of the excimer like emissions was discussed in relation to the molecular packing in the crystal. It was shown that polarized crystal fluorescence can provide insight into the excitation/emission process in the crystal. Although preliminary, this study demonstrates the potential of polarized fluorescence to elucidate the luminescent mechanism.