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) (λem, 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 PVs (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.

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

Co-facial stacking can result in aggregation-caused quenching (ACQ) in conjugated organic luminogens. This study provides an attractive 'slip-stack' self-assembly approach which can eliminate the occurrence of ACQ. The obtained results from steady-state and time-resolved optical studies, along with X-ray diffraction and computational studies demonstrate aggregation-induced emission enhancement (AIEE) of a donor-π-acceptor based 1,3-diarylpropynone, namely 1-(naphthalenyl)-3-(pyren-1-yl)prop-2-yn-1-one (PYNAP). Unlike the monomer, which exhibits poor photoluminescence in solution (φf =2 % in ACN), the twisted manifold of PYNAP allows the orientation of the molecules in a slip-stack fashion during the course of aggregation, which not only avoids a direct co-facial arrangement, but also induces augmented rigidity, leading to restricted intramolecular rotation (RIR) and enhanced emission quantum yield (φf =5 % in ACN/H2 O). The aggregation behavior of PYNAP's congener, 1-phenyl-3-(pyren-1-yl)prop-2-yn-1-one (PYPH) reinforces the hypothesis that slip-stack assembly is a useful strategy for AIEE in polycyclic hydrocarbon luminogens.