Browsing by Author "Katla, Jagadish"

The present work describes the synthesis and linear as well as nonlinear optical studies of donor-acceptor based styrylisoxazoles. Six styrylisoxazoles were synthesized, and examination of their photophysical properties reveals strong solvent polarity sensitivity due to intramolecular charge transfer characteristics. Most interestingly, we have measured large first hyperpolarizability (β) values for these styrylisoxazoles. The largest β value calculated was for the compound that bears the dimethylamine group as the donating moiety. Our current results suggest that a careful selection of the donor and acceptor groups can potentially lead to unprecedented enhancement of the (β) values of isoxazole derivatives.

A series of donor-acceptor substituted diphenylbutadienes have been synthesized and their fluorescence properties in organic solvents and imidazolium ionic liquid media were investigated. Substituted diphenylbutadienes show remarkable solvatochromic emission in polar solvents and in ionic liquids due to intramolecular charge transfer. Interestingly, diphenylbutadiene containing methoxy donor and nitro acceptor exhibits excitation dependent emission behaviour in ethanol. Excitation dependent emission studies of fluorophores in ionic liquids show distinct emission signals due to the locally excited and the charge transfer states revealing the existence of two species. Time resolved experiments show single exponential decay in organic solvents and bi-exponential decay in ionic liquids media,an indication of interaction of fluorophores with different microenvironments.

The cover feature shows organogel formation from ??cyanostilbene derivatives without auxiliary functional groups. The key component of the organogel system is pyridine acrylonitrile that forms gels either by itself (single component) or with its structural siblings (two?componentss). The organogel also acts as a sensing system for trifluoroacetic acid with distinct color changes and gelation loss.. Details are given in the Full Paper by S. Kanvah and co?workers

Pyridyl acrylonitrile without traditional auxiliary groups form stable organogels in ethanol. The addition of a second non-gelating cyanostilbene component results in a more stable two-component gel. Single crystal X-ray data reveal the influence of C−H⋅ ⋅ ⋅N, C−H⋅ ⋅ ⋅π, and π–π interactions in the formation of organogels. The morphology of the xerogels was studied by using SEM, which showed the self-assembly of molecules to fibers and sheet-like structures, and phase differences upon the gel formation and the structural phase characterization was measured using powder XRD. Exposure of the organogels to acidic (TFA) vapors results in distinct color changes and loss of gelation properties, thus highlighting the potential of these gels in sensing. The results represent a rare example of two-component organogels using two different cyanostilbene units and show that functional two-component organogels can be formed by utilizing the synergistic effects of the individual components.

A series of α-cyanostyrenes bearing anthracene and electron withdrawing trifluoromethyl units were designed and synthesized. The α-cyanostyrene skeleton favors aggregation induced enhanced emission behavior due to the restriction of intramolecular rotations. Remarkably, the anthryl cyanostyrenes bearing simple trifluoromethyl (CF3) substituents form stable organogels with enhanced fluorescence emission compared to their solution state. In water, the CF3 substituted anthrylstyrenes self-assemble into entangled fibrous nano/microstructures through intermolecular H-bonding, π-π stacking and cyano substituent interactions. The morphological features of the aggregates and the gels were substantiated using scanning electron microscopy, TEM, and powder XRD measurements. The stability of the gels was assessed using rheology investigations.

α-Cyanostyrenes bearing a planar pyrene unit and electron withdrawing trifluoromethyl units were designed and synthesized. The conformational restriction due to the presence of the cyano group on the double bond favors aggregation induced emission in aqueous media. The styrylpyrenes aggregate to form microstructures influenced by π-π stacking, cyano and CF3 substituent interactions. Importantly confluence of the pyrene ring and simple trifluoromethyl (CF3) unit allows the formation of a stable organogel with bathochromic shifts in emission. The formation of aggregates and the gel was substantiated using ¹H NMR spectroscopy and scanning electron microscopy. The stability of the gels was assessed using rheology investigations and rationalized by single crystal X-ray data.

In this work, liquid antisolvent precipitation of carbamazepine (CBZ), an anticonvulsant and antiepileptic drug, was carried out from its solutions in an ionic liquid (IL), [BMIM][Cl], using water as an antisolvent. Precipitation was carried out in the presence of ultrasound and additives such as hydroxyl propyl methyl cellulose (HPMC), bovine serum albumin (BSA), and polyvinylpyrrolidone (PVP). In-situ Raman spectroscopy was employed to uncover any polymorphic transformations that might occur in the solution during precipitation. It was found that the dihydrate (DH) form of CBZ precipitated from IL solution irrespective of the additive or the mixing condition. However, characterization of the freeze-dried CBZ powders obtained from liquid antisolvent (LAS) precipitation revealed that the DH CBZ underwent dehydration and transformed selectively to anhydrous Form III (P-monoclinic) and Form I (triclinic) in the absence and presence of additives, respectively. The additives were found to influence the final polymorphic outcome by "kinetically entrapping"the metastable Form I during dehydration. The morphology of CBZ particles obtained under all conditions was found to be long needle-like where each individual needle appeared to have been formed by aggregation of several smaller needles. Time-resolved scanning electron microscopy studies show that the morphology of CBZ particles is a result of a non-classical particle formation pathway followed by secondary nucleation and growth.

α-cyanostilbenes have attracted tremendous attention due to their unique aggregation-induced emission behavior in the aqueous media. The remarkable emission, ease of functionalization at the terminal aromatic rings, and potential applications they offer allowed the design and development of several cyanostilbene derivatives. Studies of photophysical properties revealed its use as a promising platform for diverse applications as stimuli-responsive materials. The chapter, in particular, narrates examples of organogels formed by utilizing the α-cyanostilbene framework providing a summary of recent advances in organogel formation.

Styrylisoxazoles bearing a nitro group linked to bulky aromatic rings have been synthesized and examined for their absorption and emission studies in organic solvents and water. The molecules showed emission in the visible region with significant solvatochromic emission shifts influenced by the extended conjugation of aromatic rings and intramolecular charge transfer. These absorption and emission changes were used for the efficient and sensitive detection of trace concentrations of hydrogen sulfide (H2S) through the reduction of the nitro group to the amine group in the presence of aqueous sodium sulfide. The experimental results indicated that the probes exhibit an excellent emission response with large shifts in the emission and sensitivity with a micromolar detection limit.

α-cyanostyrenes bearing a pyrene scaffold are synthesized and characterized using spectroscopic techniques. The pyrenyl styrenes are weakly emissive in solution state but show enhanced emission in water due to the formation of aggregates. The restrictions of intramolecular rotations, increased π-π interactions contribute to the strong emission of the dye molecules in the aggregated state. The formation of the aggregates, its size and morphological changes was investigated by using scanning electron microscopy (SEM) and dynamic light scattering (DLS) studies. Time-dependent density-functional theory (TDDFT) studies were also carried out and the results correlate with the experimental observations.