Effect of Slip-Stack Self-Assembly on Aggregation-Induced Emission and Solid-State Luminescence in 1,3-Diarylpropynones

Aggregation induced emission and volatile acid vapour sensing in acridine appended poly (aryl ether) based low molecular weight organogelator

Considerable research attention has been devoted to the development of portable and rapid fluorescence sensors that can selectively detect volatile acids, due to the harmful effects of acid vapour on the environment and human health. Although various types of fluorophores have been reported for sensing volatile acid vapours, regulation of the sensory response using aggregation induced emissive (AIE) based gelators has rarely been reported. In this study, we present the design and synthesis of a novel organogelator that is capable of sensing volatile acids through AIE. An acridine-attached poly(aryl ether) dendron molecular system is synthesized through an aldimine coupling reaction, which self-assembles and forms a gel, exhibiting AIE behavior. The synthesized molecule and prepared gel were characterized using NMR, MASS, XRD, HRSEM and rheology techniques. The AIE property of APD was investigated using steady-state absorption and emission spectroscopic techniques. The sensory response of the APD gelator was tested with various analytes, and the results indicated that APD shows rapid response, particularly to acid vapours, where the detection limits (DL) of trifluoroacetic acid (TFA), hydrochloric acid (HCl) and nitric acid (HNO3) vapor were as low as 0.22, 0.9 and 0.30 ppm, respectively. An APD solid film in filter paper shows a visual color change from yellow to red in an aqueous acidic medium, and the effect is reversed in an alkaline medium. These findings suggest that an APD gelator could potentially be utilized to generate a portable acid vapor sensor kit due to its low detection limit and rapid response time, and it could be also be used as a substitute for existing acid indicators.

Surfactant-induced disaggregation of a quinoxaline AIEgen scaffold: aggregation aptitude in the solid and solution states

We have designed five propellor-shaped molecules based on the quinoxaline scaffold with a functional group variation. They exhibit aggregation-induced emission, and the responses of these congeners regarding good solvents and poor solvents are investigated both spectroscopically and microscopically. Solid- as well as solution-state parallel analysis of the aggregation facet is laid out. Notably, L2 interacts specifically with a cationic surfactant, unlike other congeners where the mechanism proceeds via disaggregation. Real sample analysis was carried out on freshwater samples as well as waste effluent samples from domestic households and industries, thus projecting the analytical and environmental significance.

A Gelation-Induced Enhanced Emission Active Stimuli Responsive and Superhydrophobic Organogelator: "Turn-On" Fluorogenic Detection of Cyanide and Dual-Channel Sensing of Nitroexplosives on Multiple Platforms

A pyrene-based highly emissive low-molecular-weight organogelator, [2-(4-fluorophenyl)-3-(pyren-1-yl)acrylonitrile] (F1), is presented, which divulges thixotropic and thermochromic fluorescence switching via reversible gel-to-sol transition and tremendous superhydrophobicity (mean contact angles: 149-160°), devoid of any gelling and/or hydrophobic units. The rationale for the design strategy reveals that the restricted intramolecular rotation (RIR) in J-type self-assembly promotes F1 for the prolific effects of aggregation- and gelation-induced enhanced emission (AIEE and GIEE). Meanwhile, hindrance in charge transfer via the nucleophilic reaction of cyanide (CN^-) on the C═C unit in F1 facilitates the selective fluorescence "turn-on" response in both solution [9:1 (v/v) DMSO/water] and solid state [paper kits] with significantly lower detection limits (DLs) of 37.23 nM and 13.4 pg/cm², respectively. Subsequently, F1 discloses CN^- modulated colorimetric and fluorescence "turn-off" dual-channel response for aqueous 2,4,6-trinitrophenol (PA) and 2,4-dinitrophenol (DNP) in both solution (DL = 49.98 and 44.1 nM) and solid state (DL = 114.5 and 92.05 fg/cm²). Furthermore, the fluorescent nanoaggregates of F1 in water and its xerogel films permit a rapid dual-channel "on-site" detection of PA and DNP, where the DLs ranged from nanomolar (nM) to sub-femtogram (fg) levels. Mechanistic insights reveal that the ground-state electron transfer from the fluorescent [F1-CN] ensemble to the analytes is responsible for anion driven sensory response, whereas the unusual inner filter effect (IFE) driven photoinduced electron transfer (PET) was responsible for self-assembled F1 response toward desired analytes. Additionally, the nanoaggregates and xerogel films also detect PA and DNP in their vapor phase with reasonable percentage of recovery from the soil and river water samples. Therefore, the elegant multifunctionality from a single luminogenic framework allows F1 to provide a smart pathway for achieving environmentally benign real-world applications on multiple platforms.

A highly emissive Zn(II)-pyridyl-benzimidazolyl-phenolato-based chemosensor: detection of H2PO4-via "use" and "throw" device fabrication

2-Ethoxy-6-[1-(phenyl-pyridin-2-yl-methyl)-1H-benzoimidazol-2-yl]-phenol (HL) selectively serves as a sensitive 'turn on' Zn²⁺ sensor in 9 : 1 (v/v) DMSO/H₂O (HEPES buffer, pH = 7.4) medium in the presence of sixteen other cations at the limit of detection (LOD) of 3.2 nM. The strong blue emission of the complex, {[Zn(L¹)OAc]} (HL¹ = benzimidazolyl ring-opening structure of HL) (λ_em, 461 nm), is quenched by H₂PO₄^- in the presence of eighteen other anions and the LOD is 0.238 μM. The emission of the complex is due to restricted intramolecular rotation (RIR) followed by chelation-enhanced fluorescence (CHEF). The quenching of the emission of [Zn(L¹)OAc] by H₂PO₄^- (in the presence of other P^Vs (inorganic and biological) as well as additional anions) is due to the 'turn off' fluorescence via the demetallation and release of the nonfluorescent ligand, HL, and [Zn(H₂PO₄)]⁺. An INHIBIT logic gate memory circuit of the probe HL was devised with Zn²⁺ and H₂PO₄^- as two consecutive inputs. The percentage of H₂PO₄^- recovery was excellent and was obtained from distilled, tap, and drinking water sources. The bright blue emission of [Zn(L¹)OAc] further triggered the fabrication of ready-made portable thin films of the Zn-complex, which executed a cost-effective 'on-site' solid-state contact mode detection of H₂PO₄^- with selectivity at the picogram level (10.97 pg cm^-2) by monitoring the intensities of quenched spots under UV light upon varying the analyte concentration from 10^-8 to 10^-3 M. Finally, taking advantage of reversible fluorescence switching, a simple and definite ion-responsive security feature was successfully embedded into a "use" and "throw" solution-coated paper strip of the Zn(II)-pyridyl-benzimidazolyl-phenolato-based chemosensor, which efficiently detected H₂PO₄^- in water by a successive 'ON-OFF' fluorescence switching-driven security activity without any exhaustion of the emission phenomenon.

Aggregation-Induced Emission Active Donor-Acceptor Fluorophore as a Dual Sensor for Volatile Acids and Aromatic Amines

In the present work, a novel donor (D)-acceptor (A) fluorophore based on indeno-pyrrole derivative (PYROMe) has been utilized as a dual sensor for volatile acids and aromatic amines, where sensory responses were regulated by the aggregation-induced emission (AIE) property. The twisted structural framework of PYROMe, confirmed by crystal study, avoids closed cofacial encounter upon aggregation and aided with augmented rigidity via different noncovalent interactions that ultimately ensued restricted intramolecular rotation (RIR). Consequently, PYROMe exhibited AIE in THF/H₂O mixture along with bright solid-state emission. The accessibility of protonation at carbonyl site and feasible HOMO energy to accept electrons from aromatic amines during photoexcitation enabled PYROMe as a potential dual sensor. A thin film of PYROMe was utilized for the quantitative detection of volatile acids and aromatic amines, and the detection limit (DL) was found to be as low as 0.77 ppm and 6.04 ppb for trifluoroacetic acid (TFA) and aniline vapors, respectively. Beyond the established scopes of substituted indeno-pyrroles, the present study paves the way, for the first time, toward an AIE-driven dual-stimuli response in indeno-pyrrole based D-A fluorophores.

A Highly Efficient White Luminescent Zinc (II) Based Metallopolymer by RGB Approach

Three aryl-hydrazone O,N,O tridentate ligands with a different electron-withdrawing substituent were prepared. The introduction of a flexible charged chain in the ligands guaranteed solubility in many organic solvents and in water. The increasing withdrawing aptitude of the substituents red-shifted the emission in the correspondent metallopolymers. The metallated polymers were obtained by grafting ligand-zinc (II) coordination fragments onto commercial poly-(4-vinylpyridine). Metallopolymers thin films exhibited red, green and blue emission colors defined by Commission Internationale d'Eclairage (CIE) coordinates and medium to excellent photoluminescence (PL) quantum yields (PLQYs) comparable with other highly-performing active materials for Light-Emitting Diodes (LEDs). By grafting a suitable mix of the three different coordination pendants, an efficient single-component white emissive metallopolymer with CIE (0.30, 0.31) was prepared. Thanks to the charged moiety, the polymers resulted miscible with an ionic liquid. The addition produced homogeneous polymeric layers with unaltered PL performances, potentially employable in Light-emitting Electrochemical Cells (LECs).