Axially chiral 1,4-dihydropyridine derivatives: aggregation-induced emission in exciplexes and application as viscosity probes

An Aggregation-induced Emission Probe to Detect the Viscosity Change in Lipid Droplets during Ferroptosis

Ferroptosis is a recently identified form of cell death characterized by iron-dependent lipid peroxidation. Understanding the effects of lipid peroxidation on cellular processes during ferroptosis requires insights into lipid droplets (LDs) and their viscosity changes. To gain further insights into the intricacies of ferroptosis, it is crucial to have a fluorescent probe that targets LDs and responds to changes in viscosity. In this study, we introduce a novel LD-targeting viscosity fluorescent probe named TQE, based on the principles of aggregation-induced emission (AIE). The probe displayed AIE characteristics in tetrahydrofuran, possessing a partition coefficient (logP) of 5.87. With increased viscosity, intramolecular rotation was restricted, leading to a remarkable 3.3-fold enhancement in emission. Notably, TQE exhibited robust resistance to photo-bleaching during cellular imaging, maintaining approximately 75% of its emission intensity even after 30 min of laser irradiation. Importantly, the AIEgen could not generate hydroxyl radicals when exposed to light for up to 3 h, suggesting the low photo-toxicity of TQE to cells. Leveraging these properties, we successfully employed the probe for fluorescent imaging of the viscosity change in LDs during ferroptosis.

Substituent-Controlled Photophysical Responses in Dihydropyridine Derivatives and Their Application in the Detection of Volatile Organic Contaminants

In the ever-expanding realm of organic fluorophores, structurally simple and synthetically straightforward molecules with unique photophysical properties have received special attention. Among these, 1,4-dihydropyridine (DHP) is an important scaffold that permits fine-tuning of their photophysical properties through substituents on the periphery. Herein, we describe a series of solid-emissive N-substituted 2,6-dimethyl-4-methylene-1,4-dihydropyridine derivatives appended with electron-withdrawing substituents (dicyanomethylene or 2-dicyanomethylene-3-cyano-2,5-dihydrofuran) at the C-4 position and alkyl or alkylaryl groups on the DHP nitrogen. Electronic and steric tuning exerted by these substituents resulted in interesting photophysical properties such as negative solvatochromism, solidstate, and aggregation-induced emission (AIE). Theoretical calculations were carried out to explain the solvatochromic properties. Insight into the AIE properties was obtained through variable-temperature nuclear magnetic resonance and viscosity- and temperature-dependent emission studies. The variations in molecular packing in the crystal lattice with changes in the N-substituents contributed to the tuning of solid state emission properties. Detection of aromatic volatile organic compounds (VOCs) was achieved using the aggregates of the DHP derivatives. Among the VOCs, p-xylene elicited a significant enhancement in emission, allowing its detection at submicromolar levels.

Aggregation induced emission (AIE) molecules for measurement of intracellular temperature, pH, and viscosity sensing

This book chapter presents insightful growth and progress in the field of sensing especially, temperature, pH, and viscosity sensing. We focus more on aggregation-induced emission (AIE)-active materials for measuring intracellular pH, viscosity, and temperature by means of fluorescence and absorption study. A special emphasis is given on AIE active fluorescent molecules, molecular rotors, polymeric nanomaterials which are considered as the important aspects of sense. It also gives the fundamental and brief understanding between these different AIE active material and its application in biological systems.

Space Size-Dependent Transformation of Tetraphenylethylene Carboxylate Aggregates by Ice Confinement

Tetraphenylethylene carboxylate (TPEC) aggregates are transformed by ice confinement, which is controlled by the initial concentration of sucrose employed as a cryoprotectant and temperature. The freezing of aqueous sucrose leads to the formation of micro- or nanoliquid phase confined in ice. Aggregation-induced emission (AIE) of tetraphenylethylene carboxylate (TPEC) in the ice-confined space is explored using fluorescence spectroscopy and lifetime measurements. The characteristics of AIE in the ice-confined space strongly depend on the initial sucrose concentration and temperature, which determine the size of the liquid phase. The AIE of TPEC in the ice-confined space can be classified into three regimes in terms of spectroscopic features. Loosely packed J aggregates of TPEC are formed in the microliquid phase (>2 μm). The fluorescence intensity increases, and the wavelength is hypsochromically shifted with a decrease in the size of the space, indicating that the molecular arrangement in the aggregate depends on the space size. The fluorescence lifetimes indicate polydisperse, loosely packed aggregation. No further change in aggregate structure is observed once the liquid phase size is decreased to ∼2 μm, and a spectroscopically identical structure is maintained upon further reduction of the space size to ∼0.5 μm. The molecular arrangement in the aggregate is independent of the space size in this regime. However, when the size of the space becomes smaller than ∼0.5 μm, the aggregate structure again starts to change into a more tightly packed aggregate and a hypsochromic shift of the fluorescence wavelength occurs again. The fluorescence lifetime indicates monodispersed aggregation in this submicrospace.