A near-infrared (NIR) organic probe for rapid naked-eye detection of fluoride ions in aqueous medium.

A dihydroxy-substituted tricyanopyrroline-based near-infrared (NIR) colorimetric probe (TCP-34Hy) is developed for the effective detection of fluoride ions in aqueous medium in the presence of Ca2+ ions. The naked-eye detection (drastic color change) selectively makes the NIR colorimetric sensor more efficient. The probe can detect fluoride ions from inorganic sources (NaF/KF) as well as organic sources (TBAF) in water. The water samples from different sources, such as tap, pond, river, and sewage, have been tested successfully for fluoride ion detection using the probe (TCP-34Hy). Investigations of different kinds of soil samples (clay soil, red soil, and river sand) after pre-treatment with NaF are also productive for detection of fluoride ions in water. The probe can also detect fluoride ions in toothpaste in aqueous medium. The role of Ca2+ is discussed and explained on the basis of experimental results. Additionally, the probe (TCP-34Hy) shows high selectivity towards fluoride ion detection with a LOD of 2.3 µM (0.052 ppm) in aqueous medium.

Effect of various aqueous extracting agents on fluorescence properties of waste tea residue derived carbon dots (WTR-CDs): Comparative spectroscopic analysis.

Fluorescent carbon dots (CDs) are one of the important carbonaceous nanomaterials in the area of nanoscience and nanotechnology because of their interesting physical as well as chemical properties. Herein we studied the effect of various aqueous extracting agents on fluorescence properties of waste tea residue-based carbon dots (WTR-CDs). WTR-CDs are firstly synthesized by utilizing kitchen waste-based carbonaceous biomass. To check the role of various aqueous media during the course of WTR-CDs synthesis from carbonized carbon powder, extraction of WTR-CDs was carried out in various kinds of aqueous media viz., only aqueous (100% water, WT), aqueous-alcoholic (10% ethanol, ET), aqueous-acidic (10% acetic acid, AA), and aqueous-basic (10% ammonia, AM). The consequences of extracting agents on the photophysical properties of final WTR-CDs-WT, WTR-CDs-ET, WTR-CDs-AA and WTR-CDs-AM were also discussed in detail. We have observed interesting blue shift fluorescence spectra in acidic medium for WTR-CDs-AA and polar protic solvents compared to polar aprotic medium. The solvatochromic behaviour of WTR-CDs-WT in model polar and non-polar solvent was also studied. The effect of cationic, anionic and non-anionic surfactants on the fluorescence of WTR-CDs-WT was also evaluated. The proposed findings may help researchers in the near future to obtain fast, easy and direct synthesize CDs from a variety of biomass-based precursors under different aqueous conditions.

Applications of Carbon Dots (CDs) in Latent Fingerprints Imaging.

Carbon dots (CDs), a new member of the carbon-based material family, possess unique properties, such as high fluorescence, non-toxicity, eco-friendliness, stability and cost-effectiveness. These properties helped CDs to receive tremendous attention in various fields, namely, biological, opto-electronic, bio-imaging and energy-related applications. Although CDs are widely explored in bio-imaging and bio-sensing applications, their effectiveness in forensic science and technology is comparatively new. In this review, applications of CDs pertaining to latent FPs recovery since 2015 to 2020 is summarized comprehensively.

Coordination-Assisted Reversible Photoswitching of Spiropyran-Based Platinum Macrocycles.

Control over the stimuli-responsive behavior of smart molecular systems can influence their capability to execute complex functionalities. Herein, we report the development of a suite of spiropyran-based multi-stimuli-responsive self-assembled platinum(II) macrocycles (5-7), rendering coordination-assisted enhanced photochromism relative to the corresponding ligands. 5 showed shrinking and swelling during photoreversal, while 6 and 7 are fast and fatigue-free supramolecular photoswitches. 6 turns out to be a better fatigue-resistant photoswitch and can retain an intact photoswitching ability of up to 20 reversible cycles. The switching behavior of the macrocycles can also be precisely controlled by tuning the pH of the medium. Our present strategy for the construction of rapid stimuli-responsive supramolecular architectures via coordination-driven self-assembly represents an efficient route for the development of smart molecular switches.

J-type aggregation and thermochromic behavior of a schiff base in solution: Role of keto-enol tautomerization.

In present work, we have been investigated the thermochromism, keto-enol tautomerization, J-type aggregation and aggregation induced enhanced fluorescence (AIEF) in a single schiff base molecule (HNBzP) along with excited state intramolecular proton transfer (ESIPT) process. It is observed that keto-enol tautomerization plays an important role on thermochromism, J-type aggregation and aggregation induced enhanced fluorescence (AIEF) process in solution. From UV-Vis and fluorescence studies, J-type aggregation is observed and shows the aggregation induce enhanced fluorescence (AIEF) behaviour in solusion. The excited state intramolecular proton transfer (ESIPT) process is investigated in different solvents. Optimized geometry and electronic properties are calculated by DFT method for better understanding at molecular level.

Cluster Formation through Hydrogen Bond Bridges across Chloride Anions in a Hydroxyl-Functionalized Ionic Liquid.

Several recent studies of hydroxyl-functionalized ionic liquids (ILs) have shown that cation-cation interactions can be dominating these materials at the molecular level when the anion involved is weakly interacting. The hydrogen bonds between the like ions led to the formation of interesting chain-like, ring-like, or distinct dimeric (i. e. two ion pairs) supermolecular clusters. In the present work, vibrational spectroscopy (ATR-IR and Raman) and density functional theory (DFT) calculations of the hydroxyl-functionalized imidazolium ionic liquid C2 OHmimCl indicate that anion-cation hydrogen bonding interactions are dominating, leading to the formation of distinct dimeric ion pair clusters. In this arrangement, the Cl- anions function as a bridge between the cations by establishing bifurcated hydrogen bonds with the OH group of one cation and the C(2)-H of another cation. Cation-cation interactions, on the other hand, do not play a significant role in the observed clusters.

Temperature sensor probe based on intramolecular charge transfer (ICT) & reversible solute-solvent interaction in solution.

In this present work, we have developed a temperature sensitive ICT probe (KNP) to investigate alternation of ICT process with the temperature in polar protic solvents. The H-bonding interaction is found to play a key role on solute-solvent interaction to become a temperature sensitive ICT probe in solution. From temperature dependent UV-Vis spectra, it is cleared that the solute-solvent interaction is reversible in nature with temperature and affected by concentration in polar protic solvents. The reversible solute-solvent interaction is observed by monitoring the intensity variation of intramolecular charge transfer (ICT) band with temperature in solution.

Evidence of C--F-P and aromatic π--F-P weak interactions in imidazolium ionic liquids and its consequences.

A simple change from alkyl group to alkene in side chain of imidazolium cation with same anion resulted in a drastic impact on physical properties (e.g., melting point) from bmimPF6 IL to cmimPF6 IL. The underlying reasons have been elucidated by structural and interaction studies with the help of DSC, SCXRD, vibrational and multi-nuclear NMR spectroscopic techniques. Experiments reveal existence of new weak interactions involving the carbon and π cloud of the imidazolium aromatic ring with fluoride of PF6 anion (i.e., C2--F-P and π--F-P) in cmimPF6 but are absent in structurally similar prototype IL, bmimPF6. Though weak, these interactions helped to form ladder type supramolecular arrangement, resulting in quite high melting point for cmimPF6 IL compared to bmimPF6 IL. These findings emphasize that an IL system can behave uniquely because of the existence of uncommon weak interactions.

Microheterogeneity in imidazolium and piperidinium cation-based ionic liquids: 1D and 2D NMR studies.

Existence of microheterogeneity of imidazolium and piperidinium cation-based ionic liquids (ILs) containing PF6 and NTf2 anions has been investigated by 1D and 2D NMR spectroscopy. 2D NMR (especially NOESY and HOESY) has been employed for studying the interactions present between cation and anion as well as the intermolecular interaction among cations. HOESY spectrum shows that fluorine of anion ( PF6- and NTf2-) significantly interacts with proton of the cations. Combined results of HOESY and NOESY for imidazolium IL indicate that the PF6- and imidazolium cation are distributed in organized manner, resulting a heterogeneous environment in liquid state. We have also observed existence of heterogeneous environment for piperidinium cation-based ILs which is different from imidazolium ILs. It appears that existence of microheterogeneity in IL is ubiquitous and therefore open up the ILs field to revisit. Copyright © 2017 John Wiley & Sons, Ltd.

Manipulating the proton transfer process in molecular complexes: synthesis and spectroscopic studies.

The proton transfer process in carefully designed molecular complexes has been investigated directly in the solid and solution phase. SCXRD studies have been employed to investigate the N-H-O bonding interaction sites of the molecular complexes, with additional experimental support from FTIR and Raman spectroscopic studies, to gain information on the relative position of hydrogen in between the N and O centers. Further, the proton transfer process in solution is studied using UV-Visible spectroscopy through monitoring the intramolecular charge transfer (ICT) process in these molecular complexes, which is primarily governed by the number of electron withdrawing groups (nitro groups) on proton donor moieties (NP, DNP and TNP). It is found that the magnitude of the ICT process depends on the extent of proton transfer, which on the other hand depends on the relative stabilities of the constituent species (phenolate species). A correlation is observed between an increase in the number of nitro groups and an increase in the melting point of the molecular complexes, indicating the enhancement of ionic character due to the proton transfer process. The aliphatic H-bonding is identified and monitored using (1)H-NMR spectroscopy, which reveals that the identity of molecular complexes in solution interestingly depends on the extent of proton transfer, in addition to the nature of the solvents. The aliphatic C-H-O H-bonding interaction between the oxygen atom of the nitro group and the alkyl hydrogen in piperidinium was also found to play a significant role in strengthening the primary interaction involving a hydrogen transfer process. The conductivity of the molecular complexes increases with an increase in the number of nitro groups, indicating the enhancement in ionic character of the molecular complexes.

Anion directed structural diversity in zinc complexes with conformationally flexible quinazoline ligand: structural, spectral and theoretical studies.

In this paper, we report the synthesis, structure and photophysical studies of four new complexes of conformationally flexible 6-chloro-4-phenyl-2-(pyridin-2-yl)quinazoline ligand (L) with Zn(ii). The coordinating ability of the ligand and geometrical preferences of the resultant complexes are tuned by varying the anion of the metal salt as confirmed by structural and DFT studies. The choice of the metal salt (especially anion) directs the stabilisation of different conformations of the ligand arising out of twisting of the pyridyl ring with respect to the quinazoline ring, resulting in complexes with different nuclearity (monomer/dimer) as well as different coordination geometries (tetrahedral/trigonal bipyramidal/octahedral). Photophysical properties are also found to be tuned due to conformational changes on complexation. DFT studies on the ligand establish the conformationally stable forms as observed in the reported structures.

Significance of weak interactions in imidazolium picrate ionic liquids: spectroscopic and theoretical studies for molecular level understanding.

The effects of interionic hydrogen bonding and π-π stacking interactions on the physical properties of a new series of picrate anion based ionic liquids (ILs) have been investigated experimentally and theoretically. The existence of aromatic (C2-HO) and aliphatic (C7-HO-N22 and C6-HO-N20) hydrogen bonding and π-π stacking interactions in these ILs has been observed using various spectroscopic techniques. The aromatic and aliphatic C-HO hydrogen bonding interactions are found to have a crucial role in binding the imidazolium cation and picrate anion together. However, the π-π stacking interactions between two successive layers are found to play a decisive role in tight packing in ILs leading to differences in physical properties. The drastic difference in the melting points of the methyl and propyl derivatives (mmimPic and pmimPic respectively) have been found to be primarily due to the difference in the strength and varieties of π-π stacking interactions. While in mmimPic, several different types of π-π stacking interactions between the aromatic rings (such as picrate-picrate, picrate-imidazole and imidazolium-imidazolium cation rings) are observed, only one type of π-π stacking interaction (picrate-picrate rings) is found to exist in the pmimPic IL. NMR spectroscopic studies reveal that the interaction of these ILs with solvent molecules is different and depends on the dielectric constant of the solvent. While an ion solvation model explains the solvation in high dielectric solvents, an ion-pair solvation model is found to be more appropriate for low dielectric constant solvents. The enhanced stability of these investigated picrate ILs compared with that of inorganic picrate salts under high doses of γ radiation clearly indicates the importance of weak interionic interactions in ILs, and also opens up the possibility of the application of picrate ILs as prospective diluents in nuclear separation for advanced fuel cycling process.