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Presently, we are working on weak intermolecular interaction (aliphatic H-bonding and ?-? stacking interaction) in imidazolium and piperidinium-based ionic liquids. The weak interactions play a crucial role in the physical properties of ILs. Further, the significance of weak interactions on cluster formation and extended intermolecular interaction in these ILs have been investigated in our laboratory. The vibrational spectroscopic techniques (Raman and FTIR) have been employed to understand the effect of H-bonding interaction on physical property and molecular cluster formation of ILs. Further, DFT calculations help for better understanding the intermolecular interactions at the molecular level.

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.

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.

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.

The phenol dimer is a prototype molecular cluster system and is considered as a low-barrier H-bond (LBHB) interaction. The phenol dimer influences and catalyses various transformation in biological system but not identified in solid state yet. In present study, p-nitrophenol dimer (NPD) has been identified in the solid state. N-methylpiperidine (MP) is used to stabilise the NPD dimer and formed a stable MPH(PDA) molecular complex. Instead of p-nitrophenol dimer (NPD), the effect of the nitro group, the role of N-methylpiperidine (MP) and H-bonding interaction in MPH(PDA) have been investigated directly by experimental and theoretical studied. It is observed that extent of π electron delocalisation on p-nitrophenol play an important role on stability of p-nitrophenol dimer (NPD).

Photophysical study of highly photoactive bis-2-benzylidenemalononitrile (BBM) has been investigated in solution using UV–vis, fluorescence and NMR spectroscopic techniques. The seletive photodissociation can be attributed to the presence of highly polarized C C bond, attached to dicyno groups (CN). Nevertheless, the observed photodissociation of BBM is highly solvent specific and temperature sensitive. The product A (2-(4-formylbenzylidene)malononitrile), formed by the selective photodissociation of BBM under UV irradiation has been isolated and identified by NMR studies. The photodissociation followed the pseudo 1st order kinetics with a rate constant (k) 10−3-10-4.s-1. Moreover the mechanistic study of selective photodissociation of bis-2-benzylidenemalononitrile (BBM) has been investigated and found to follow the dipolar mechanism path during photochemical reaction.

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.

Our main focus is to report the tribological properties of ionic liquids (ILs). Mainly, lubricating of ILs has been reported to understand the applicability of ionic liquids (ILs) in petroleum-based lubricant industry and energy conversion process as oil additive. The influence of counter parts of ILs on tribological property has been reported for designing efficient lubricating and oil-additive property of ILs. The effect of halogenated and nonhalogenated ILs on corrosion is also reported during tribological studies at different metal surface. Further, role of ILs as oil-additive has been discussed in terms of better tribological performance. Structure modification and role of anion on better performance of tribological property have been mentioned for enhancing effectiveness of lubricant and oil-additive properties. Origin of corrosion and thin film formation on metal surface are also discussed in detailed using different types of ILs and metal surfaces.

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.

Two series of new 3d-4f heterodinuclear [Zn II Ln III ] Schiff base complexes of general formula [Zn( µ -L1)( µ -CH 3 COO)Ln(NO 3 ) 2 (S)] [Ln = Pr ( 1 ), Nd ( 2 ), Sm ( 3 ), Gd ( 4 ); S = MeOH; H 2 L1= N,N-bis(3-methoxysalicylidene)-1,4-diaminobutane] and [Zn( µ -L2)( µ -CH 3 COO)Ln(NO 3 ) 2 (S)] [Ln= Pr ( 5 ), Nd ( 6 ), Sm ( 7 ), Gd ( 8 ), S= MeOH; H 2 L2= N,N-bis(3-ethoxysalicylidene)-1,4-diaminobutane] are synthesized and fully characterized. Complexes 1 , 2 , 3 , 4 , 5 & 7 are structurally characterized by single crystal X-ray crystallography. The crystallographic investigation indicates that the complexes contain 9 and 10-coordinated Ln III ions, while the Zn II ions always display a distorted square-pyramidal geometry. The crystal structure of the complexes are stabilized by inter molecular extended hydrogen bonding and C-H····π interactions resulting in supramolecular frameworks. Luminescence studies for the heterodinuclear compounds containing Nd III & Sm III reveal that the Zn-complex moiety acts as antenna for the emission from Ln III ions. In addition to the ligand-centered emission in the UV–Vis region, complex 2 (having Nd III ) exhibits emission in NIR region also, thus resulting a new NIR emitting material.

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.

Aggregation behavior of push-pull salen-type schiff base (BIHyDE) in different solvents at ground and excited state, has been investigated. At ground state, lower energy absorption band is suppressed during concentration dependent UV-Vis study in CHCl3 solution. The broadening of lower energy emission band is observed during concentration dependent fluorescent study in CHCl3 solution. Interestingly, fluorescence life time of BIHyDE in solution is also altered during concentration dependent fluorescence study in CHCl3 solvent. Similar aggregation is also observed at ground and excited state in ACN solvent. Dipolar state and intermolecular dipolar interaction of BIHyDE molecule highly influence towards strong aggregation process and orientation of molecule in solution. Ground state and excited state optical properties are highly influenced by concentration of push-pull salen-type schiff base (BIHyDE) in different solvents.

The significance of intermolecular classical and non-classical H-bonding interactions in the stabilization of a naphthalene core based conformationally rigid cleft-shaped 1,5-dioxocin (BNAP) is presented here. The importance of H-bonding interactions to account for the unusual stability of a catalytically important novel molecule is reported for the first time. In addition to strong CH⋯π interactions, the formation of the unique intermolecular seven-membered H-bonded ring in the crystalline state through classical and non-classical H-bonding interaction was found to provide the unusual stability. This supramolecular structure was also found to impart stability in the presence of a strong acid as evident from the detailed UV-Visible spectroscopic studies. In addition to DFT calculations, the Hirshfeld surfaces, mapped with dnorm, and 2D fingerprint plots, support the existence of these classical and non-classical H-bonding and CH⋯π interactions. Furthermore, BNAP shows its remarkable catalytic activity for the Knoevenagel condensation reaction.

The intramolecular charge transfer (ICT) process in donor–acceptor systems has tremendous importance in various physical and biological systems. Three nitrophenolate salts were synthesized and studied here. The ICT and π → π* transition processes were identified in these derivatives using UV-Vis spectroscopy and theoretical calculations. It was observed that by simple substitution with nitro groups, one can generate and control the ICT process by regulating the charge distribution over the molecule. While for a monosubstitute nitro derivative, only one ICT band was observed, additional ICT processes can be generated at will by introducing a second nitro group. The intensity of this second ICT channel can be regulated with introduction of a third nitro group. Further, the association constants and solvation processes for these potassium nitrophenolate derivatives were found to be drastically dependent on the number of ICT channels present in the molecule. Theoretical studies (MEP analysis) support the experimental observations presented here. The results show that by simply introducing additional acceptor groups to the system, one can tune the ICT band efficiently in a conjugate system.

Two new di-cationic imidazolium based ionic liquids (ILs) containing chloride, (bisImCl), or hexafluorophosphate anions (bisImPF6) have been synthesized and characterized by FT-Raman and 1H- and 13C NMR spectroscopies. The p-xylyl group acts a spacer between two imidazolium rings in the cation. The influence of the anions on thermal properties of the compounds has been investigated. Both bisImCl and bisImPF6 have shown good thermal stability up to at least 280 °C. Intermolecular and cation-anion interactions have been investigated by NMR spectroscopy. B3LYP/6-311++G∗∗ calculations have optimized the structure of bisIm cation with both anions. Both Cl are found to be in a monodentate coordination, while in bisImPF6 only one PF6 group presents monodentate coordination. AIM calculations at the same level of theory have evidenced a higher number of interactions in bisImPF6, as compared to bisImCl. A complete assignment of the vibrational frequencies for the cation, bisImCl and bisImPF6 are here reported together with a set of harmonic scaled force constants calculated for the cation and bisImCl. Further, polarizability (α) and the static first hyperpolarizabilities (β) of these ILs are calculated by different DFT functionals in order to understand nonlinear optical (NLO) properties. It is observed an inverse correlation between the predicted β value and the HOMO-LUMO energy difference (Δe) from two state models. The high gap value observed for bisImPF6 justifies its low reactivity, as supported by the high number of interactions predicted for this ionic liquid.

In present work, photodissociation kinetics of selective C C bond in BBM is investigated in different micelles concentration. In polar solvents, rate of photodissociation (k) is relatively lower compared to H2O solvent under similar condition. The rate of photodissociation (k) is enhanced with increase of aqueous CTAB concentration and found to be highly sensitive to aqueous CTAB concentration. It is clear that micelle concentration and hydrophobic region plays significant role on enhancing rate of photodissociation. Crucial role of hydrophobic region in micelle has been discussed and confirmed by experimental results.

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.

In present work, 2-(4-Hydroxybenzylidene)malononitrile (HyDC) acts as a photoacid and intramolecular charge transfer (ICT) probe for monitoring solvent specific ground state proton transfer (GSPT) process from solute to solvents. Presence of electron accepting group in HyDC, photoacidic nature and GSPT process are enhanced and observed by UV–Vis spectroscopy. HyDC shows microsolvation behavior with protic solvents at ground state. Microsolvated clusters of HyDC with solvents are formed and supported by experimental and theoretical results.

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 C 2 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.

Interonic interactions determine the macroscopic properties of ionic liquids (ILs). Hence, unravelling the relationships between the microscopic and macroscopic scales is key for rational design. Combining density functional theory (DFT) calculations of isolated ion pairs and vibrational spectroscopy of the condensed phase (fluid or solid) has become a very common approach. In the present work, we make a step towards understanding how the physicochemical effects in small gas phase clusters of a hydroxyl functionalized imidazolium-picrate IL relate with the molecular structure and interactions of the corresponding solid material taking 1-hydroxyethyl-3-methylimidazolium picrate, C2 OHmimPic, as an example. In the isolated ion pair, strong alkyl-OH⋅⋅⋅Pic hydrogen bonding interactions are found rather than the commonly observed hydrogen bonding interactions at the slightly acidic C(2)-H site of the imidazolium ring. However, this part of the cation plays an important role when clusters of ion pairs in the gas phase and inside a crystal lattice are considered. For example, in the dimeric ion-pair cluster, one centre (O*) with two interaction sites (C(2)-H-O* and alkyl OH-Pic) is observed. This configuration is suggested by single crystal X-ray diffraction (XRD), vibrational spectroscopy, and the dispersion-corrected DFT calculations. Hence, the study provides evidence for the appearance of theoretical gas phase clusters in an actual solidified ionic liquid. This ion pair dimer formation may be a general behavior of hydroxyl functionalized imidazolium ILs, but further research is needed to draw a final conclusion. Moreover, the Raman spectra confirm the exclusive gauche conformation of the hyroxyl functionalized alkyl chain.

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–H⋯O) and aliphatic (C7–H⋯O–N22 and C6–H⋯O–N20) hydrogen bonding and π–π stacking interactions in these ILs has been observed using various spectroscopic techniques. The aromatic and aliphatic C–H⋯O 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.

A series of molecular complexes have been designed, synthesized and used as organo-catalysts for the first time for very efficient Knoevenagel condensation. Molecular complexes are thermally stable, easily recyclable, and have a low cost of preparation. The role of acidic protons in molecular complexes in Knoevenagel condensations has been identified as the key factor and helps us to provide useful information about the reaction pathway. The acidic proton of a catalyst enhances the electrophilicity of an aldehyde and accelerates the dehydration process of the reaction at room temperature (RT). An eco-friendly, green synthetic protocol for the Knoevenagel condensation is used to synthesize a series of important cyano group containing synthetic precursors for synthesis of biologically active molecules at RT using a minimum amount of catalyst (∼5 mol%) without the need for chromatographic separation techniques. Detailed mechanistic studies and substituent effects of aromatic aldehydes on the reaction have been investigated. In addition, biologically active 2-amino-4H-chromene derivatives have also been synthesized by the Knoevenagel condensation of salicylic aldehydes with active methylene compounds, followed by intramolecular cyclization (via Michael addition) delivering higher yields within shorter reaction times at RT without any need for chromatographic separation.

Existence of microheterogeneity of imidazolium and piperidinium cation-based ionic liquids (ILs) containing PF

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.

An efficient and one-pot three-component strategy for synthesizing highly functionalized quinazoline derivatives is presented. A mixture of 2-aminobenzophenone, aromatic aldehyde and ammonium acetate in the presence of I2-catalyst provides desired products in excellent yields even at moderate temperature (40 °C) without the involvement of any chromatographic purification. Oxidizing and Lewis acidic properties of molecular I2 have been utilized here. Detailed mechanism has been established based on an isolated intermediate and its single crystal X-ray crystallographic structure.

The efficient one-pot procedure allows the synthesis of quinazoline derivatives (18 examples) in

Three quinazoline based small molecules showed global upregulation of miRNA expression with a selective enrichment of tumor suppressor miRNAs. The target genes of the upregulated miRNAs were predicted to be enriched for apoptotic pathways. Apoptotic induction following treatment with quinazoline compounds was confirmed by in cellulo studies. Thus, these small molecules having the core structural moiety (2,4-diphenyl-quinazoline) can be used as scaffolds to design activators of miRNA expression paving the way for novel anti-cancer drugs.

An atom-efficient, eco-friendly, solvent-free, high yielding, multicomponent green strategy to synthesize highly functionalized quinazoline derivatives by the one-pot reaction of 2-aminobenzophenone, aromatic aldehyde and ammonium acetate is presented. Magnetic IL, butylmethylimidazolium tetrachloroferrate (bmim[FeCl4]) has been used successfully as a catalyst in a multicomponent synthetic strategy for the first time. The catalytic cycle and a tentative reaction mechanism were discussed and experimentally verified. Structural and optical properties of the synthesized quinazolines are also described.