Two AIEE-active α-cyanostilbene derivatives containing BF2 unit for detecting explosive picric acid in aqueous medium

AIEE Active Azomethine-Based Rhodamine Derivative For Ultrasensitive Multichannel Detection of Au3+ Through a Fluorimetrically, Electrochemically, and RGB-Based Sensing Assay

In this study, a novel rhodamine-based optically and electrochemically active chemosensor, integrated with a p-DMAC moiety, demonstrated extremely selective identification of Au³⁺ ions relative to other metal species, including (Li⁺, Na⁺, K⁺, Ba²⁺, Ca²⁺, Mg²⁺, Co²⁺, Mn²⁺, Zn²⁺, Pb²⁺, Ni²⁺, Fe²⁺, Hg²⁺, Fe³⁺, Cd²⁺, Pd²⁺, Al³⁺, Cr³⁺, Cu²⁺, and nitrate salt of Ag⁺). These compounds demonstrated a novel and outstanding aggregation-induced emission enhancement (AIEE) behavior by aggregating in DMF/H₂O medium. Furthermore, the degree of quenching was varying linearly with a Au³⁺ concentration from 0 to 40 nM, with a lower detection limit by RH-DMAC nanoaggregates of 118.79 picomolar (40.35 ppm). The Stern-Volmer plots, Job's plot, Benesi-Hildebrand plot, ¹H NMR titrations, ESI-mass, and FTIR all revealed significant interactions between the sensor and Au³⁺. Moreover, the proposed electrochemical sensor afforded a linear correlation before the peak current and concentration of Au³⁺ in the range of 0-40 nM, with a detection limit of 483.73 pM or 164.36 ppt (by cyclic voltammetry method) and 298.0 pM or 101.24 ppt (by the Differential Pulse Voltammetry method). Furthermore, the proposed sensing assay was used to measure Au³⁺ ion in spiked water samples (tap, drinking, waste, and river water), achieving acceptable accuracy and precision with high recovery rates. Furthermore, RH-DMAC-coated fluorescence paper test strips were designed for on-site Au³⁺ detection. Apart from this, the use of smartphone-based RGB (Red Green Blue) color analysis shortened the operating process, accelerated the detection technique, and provided a novel methodology for the instantaneous, real-time examination of Au³⁺ in real water samples.

Triphenylamine-based small-molecule fluorescent probes

Ammonia with the three hydrogens substituted by phenyls is known as triphenylamine (TPA), and is one of the most useful compounds because of its vast practical applications. Chemists have produced thousands of TPA derivatives to date. Because of its biocompatibility and structural features, it has been widely used in the fields of molecular recognition, molecular imaging, materials chemistry, and also in biology and medical science. Its strong electron-donating ability encourages scientists to produce different types of probes for molecular recognition. This review is based on recent developments and advances in TPA-based small molecular fluorescent probes within the time period 2010-2021. This extensive review may expedite improvements in more advanced fluorescent probes for vast and stimulating applications in the future.

Dual-state emission difluoroboron derivatives for selective detection of picric acid and reversible acid/base fluorescence switching

A novel difluoroboron derivative (TPEBF) containing α-cyanostilbene and tetraphenylethylene units has been designed and synthesized. TPEBF emits strong fluorescence both in dilute solutions (Φ_FL = 19.3% in THF) and in the solid state (Φ_FL = 49.3%), which is significantly distinct from the case of the aggregation-caused quenching (ACQ) and aggregation-induced emission (AIE) chromophores. The dual-state emission properties of the compound overcome the limitation of single-state luminescence and enable it to be used in both solid and solution states. TPEBF with strong emission in solution is utilized for sensing picric acid (PA) with high selectivity and sensitivity in THF (LOD = 497 nM) and aqueous media (LOD = 355 nM). The mechanism was described for the synergy of fluorescence resonance energy transfer (FRET) and photoinduced energy transfer (PET) based on the UV-vis absorption and fluorescence spectra, ¹H NMR and theoretical calculations results. On the other hand, the highly efficient emission in the solid state allows the compound to be cast on paper to switch external acid/base stimuli.

A perylene monoimide probe based fluorescent micelle sensor for the selective and sensitive detection of picric acid

A hydroxyl functionalized perylene monoimide probe (PMI-OH) was prepared and self-assembled with the nonionic surfactant Triton X-100 (TX100) to fabricate a fluorescent micelle sensor for the selective and sensitive detection of picric acid (PA), a common explosive and environmental pollutant. The synthesized PMI-OH probe exhibited excimer fluorescence emission, and the intensity of the excimer fluorescence emission was significantly enhanced after the PMI-OH probe formed micelles with TX100. The obtained PMI-OH@TX100 micelles presented excellent photoluminescence properties and had a maximum fluorescence emission at 630 nm. The red fluorescence of the PMI-OH@TX100 micelles was quenched upon introduction of the nitro explosive PA due to electron transfer from the donor (PMI-OH) to the acceptor (PA). The fluorescence quenching of the fluorescent micelle sensor was proportional to the concentration of PA in the range of 2 to 10 μM. The limit of detection was 500 nM using 3σ/k. Thus, the developed PMI-OH@TX100 micelle sensor has great potential to detect PA in ordinary samples.

Fabrication of deoxycholic acid tethered α-cyanostilbenes as smart low molecular weight gelators and AIEE probes for bio-imaging

Four novel deoxycholic acid tethered α-cyanostilbenes were designed, synthesized and characterized using detailed spectroscopic analysis. The synthesized deoxycholic acid tethered α-cyanostilbene derivatives formed stable gels with a variety of solvents, such as xylene, toluene, mesitylene, decane, dodecane etc. The stable gels showed lamellar sheet type structures stacked over each other, consisting of entangled fibres as evident from SEM, TEM and Fluorescence Microscopy images; The synthesized compounds exhibited AIEE behaviour in H₂O/THF mixture, with the maximum emission observed in 70% H₂O/THF fraction along with a bathochromic shift. A solvent thickening experiment was perform to establish the mechanism of AIEE and the AIEE property was explored for bacterial bio-imaging. The synthesized derivatized steroids proved their potential as multifunctional organic materials.