Prasun Mukherjee

Lanthanide sensitization in II-VI semiconductor materials: a case study with terbium(III) and europium(III) in zinc sulfide nanoparticles.

This work explores the sensitization of luminescent lanthanide Tb(3+) and Eu(3+) cations by the electronic structure of zinc sulfide (ZnS) semiconductor nanoparticles. Excitation spectra collected while monitoring the lanthanide emission bands reveal that the ZnS nanoparticles act as an antenna for the sensitization of Tb(3+) and Eu(3+). The mechanism of lanthanide ion luminescence sensitization is rationalized in terms of an energy and charge transfer between trap sites and is based on a semiempirical model, proposed by Dorenbos and co-workers (Dorenbos, P. J. Phys.: Condens. Matter 2003, 15, 8417-8434; J. Lumin. 2004, 108, 301-305; J. Lumin. 2005, 111, 89-104. Dorenbos, P.; van der Kolk, E. Appl. Phys. Lett. 2006, 89, 061122-1-061122-3; Opt. Mater. 2008, 30, 1052-1057. Dorenbos, P. J. Alloys Compd. 2009, 488, 568-573; references 1-6.) to describe the energy level scheme. This model implies that the mechanisms of luminescence sensitization of Tb(3+) and Eu(3+) in ZnS nanoparticles are different; namely, Tb(3+) acts as a hole trap, whereas Eu(3+) acts as an electron trap. Further testing of this model is made by extending the studies from ZnS nanoparticles to other II-VI semiconductor materials; namely, CdSe, CdS, and ZnSe.

Optimizing sensitization processes in dinuclear luminescent lanthanide oligomers: selection of rigid aromatic spacers.

This work illustrates a simple approach for optimizing the lanthanide luminescence in molecular dinuclear lanthanide complexes and identifies a particular multidentate europium complex as the best candidate for further incorporation into polymeric materials. The central phenyl ring in the bis-tridentate model ligands L3–L5, which are substituted with neutral (X = H, L3), electron-withdrawing (X = F, L4), or electron-donating (X = OCH3, L5) groups, separates the 2,6-bis(benzimidazol-2-yl)pyridine binding units of linear oligomeric multi-tridentate ligand strands that are designed for the complexation of luminescent trivalent lanthanides, Ln(III). Reactions of L3–L5 with [Ln(hfac)3(diglyme)] (hfac– is the hexafluoroacetylacetonate anion) produce saturated single-stranded dumbbell-shaped complexes [Ln2(Lk)(hfac)6] (k = 3–5), in which the lanthanide ions of the two nine-coordinate neutral [N3Ln(hfac)3] units are separated by 12–14 Å. The thermodynamic affinities of [Ln(hfac)3] for the tridentate binding sites in L3–L5 are average (6.6 ≤ log(β(2,1)(Y,Lk)) ≤ 8.4) but still result in 15–30% dissociation at millimolar concentrations in acetonitrile. In addition to the empirical solubility trend found in organic solvents (L4 > L3 >> L5), which suggests that the 1,4-difluorophenyl spacer in L4 is preferable, we have developed a novel tool for deciphering the photophysical sensitization processes operating in [Eu2(Lk)(hfac)6]. A simple interpretation of the complete set of rate constants characterizing the energy migration mechanisms provides straightforward objective criteria for the selection of [Eu2(L4)(hfac)6] as the most promising building block.

Triton-X-100 catalyzed synthesis of 1,4-dihydropyridines and their aromatization to pyridines and a new one pot synthesis of pyridines using visible light in aqueous media

A realistic and convenient synthetic method has been developed for the facile synthesis of 1,4-dihydropyridine derivatives in the presence of the non-ionic surfactant Triton X-100, in an aqueous medium at room temperature. A greener method to synthesize pyridine derivatives has also been developed by the oxidation of 1,4-dihydropyridine derivatives with almost 100% yields and also in a one pot synthesis, employing an aldehyde, ethyl acetoacetate and ammonium acetate in an aqueous micellar medium by irradiation with potassium persulphate in the presence of visible light. The one pot protocol offered excellent yields of the targeted product in a very short period of time at room temperature and the non-ionic surfactant catalyst can be recovered very easily. We also observed that during the reaction there was the formation of micelles, or micelle-like colloidal aggregates, from the non-ionic surfactant and the reaction mixture in water, measured by dynamic light scattering and visualized through an optical microscope. The process is advantageous as ammonia is generated from an ammonium salt under absolutely neutral conditions and the product purification follows a group assistant purification chemistry process (GAP).

Lanthanide cation-induced tuning of surface capping properties in zinc sulfide nanoparticles: an infrared absorption study

This study reveals the tuning of the vibrational characteristics of the capping ligands in lanthanide [Ln = Sm, Eu, Tb, Dy] cation-incorporated zinc sulfide nanoparticles, Zn(Ln)S, as monitored by Fourier transform infrared (FTIR) spectroscopy. Both stearate and trioctylphosphine oxide (TOPO) were found to act as surface-capping ligands for nanoparticles with multiple coordination environments. The vibrational characteristics of the capping ligands in the undoped ZnS nanoparticles exhibited noticeable differences in absorption as compared to those of the pure zinc stearate and TOPO molecules. Lanthanide cation incorporation tunes the corresponding vibrational characteristics to a significant extent, as compared to that in the undoped ZnS nanoparticles. It has been argued that the observed tuning of the capping ligand IR absorption characteristics is induced by the lanthanide cations that are located near or on the surface of the nanoparticles. The IR spectra suggest a probable change of carboxylate coordination environment in the Zn(Ln)S nanoparticles. The results obtained from the ZnS-based nanoparticles were analyzed based on a semi-quantitative analysis and compared with those from ZnSe and Zn(Tb)Se nanoparticles, in order to evaluate the effect of the constituent anion of the nanoparticles in modulating the IR signature.

Practical carbocatalysis by graphene oxide nanosheets in aqueous medium towards the synthesis of diversified dibenzo[1,4]diazepine scaffolds

GO nanosheets are found to be an efficient recyclable carbocatalyst for the construction of diversified dibenzo[1,4]diazepine nuclei starting from o-phenylenediamine, various aldehyde/ketone and 1,3-diketo compounds in aqueous medium. This new metal free synthetic protocol also facilitated the formation of coumarine and quinolinone fused novel dibenzo[1,4]diazepines and provided an excellent yield of the corresponding products. In addition, when a substrate contains both the aldehyde and ketone functionality, the reacton offers dibenzo[1,4]diazepines resulting from the chemoselective aldehyde adduct.

Spirocyclopropanes from Intramolecular Cyclopropanation of Pyranopyrazoles and Pyranopyrimidine-diones and Lewis Acid Mediated (3 + 2) Cycloadditions of Spirocyclopropylpyrazolones

A robust intramolecular cyclopropanation reaction was first performed on pyranopyrazole and pyranopyrimidine-dione derivatives to obtain spirocyclopropylpyrazolones and barbiturates, using iodosylbenzene (PhIO) or the combination of iodobenzene diacetate (PIDA)/molecular iodine (I2), under mild reaction conditions. Syntheses of functionally and stereochemically diversified, novel spiropyrazolone fused 2-iminothiophene and spiropyrazolone fused pyrroline scaffolds were also demonstrated via Lewis acid catalyzed highly diastereoselective (3 + 2) cycloaddition reactions of the synthesized spiro-cyclopropyl pyrazolones with phenyl isothiocyanate and benzonitrile, respectively.

Towards the realization of luminescence from visible emitting trivalent lanthanides (Sm, Eu, Tb, Dy) in polar zinc sulfide nanoparticles: evaluation of in vitro cytotoxicity

This work reports on the realization of luminescence from four visible emitting trivalent lanthanide (Ln) cations [samarium (Sm), europium (Eu), terbium (Tb) and dysprosium (Dy)] in polar zinc sulfide nanoparticles, Zn(Ln)S. Among the Zn(Ln)S nanoparticles studied, noticeable lanthanide cation centered luminescence has only been realized from the Zn(Tb)S and Zn(Eu)S nanoparticles in water, whereas no such effect has been observed in the corresponding Sm and Dy containing nanoparticles. In all the nanoparticles with characteristic lanthanide luminescence, the nanoparticles were found to be acting as an optical antenna and protector matrix, in order to realize luminescence from the respective lanthanide cations. The results have been rationalized with the lanthanide cations acting as charge (hole and/or electron) traps in the semiconductor nanoparticle matrix along with associated environmental effects. A comparison of the corresponding hydrophobic Zn(Tb)S nanoparticles reveal significant differences in photophysical properties. Finally, the hydrophilic Zn(Tb)S nanoparticles have been examined for in vitro cytotoxicity and the results indicate potential anti-cancer therapy for human mammary adenocarcinoma cells (MDA-MB-231) with the capability of cellular imaging.

How Important is the Host (Semiconductor Nanoparticles) Identity and Absolute Band Gap in Host-Sensitized Dopant Photoluminescence?

This work reports the host (semiconductor nanoparticles) sensitized dopant (lanthanides, Ln) photoluminescence in near band gap matched Sn(Ln)O2 and Zn(Ln)S [Ln = Sm, Tb] nanoparticles to address the importance of the nanoparticle identity and absolute band gap in the underlying process. While the sensitization was evident in the Sn(Sm)O2 and Zn(Tb)S nanoparticles, the same was not observed in the Sn(Tb)O2 and Zn(Sm)S nanoparticles. This observation stresses the importance of nanoparticle identity as the determining factor in realizing the host-sensitized dopant photoluminescence and provides important insight into developing novel doped inorganic nanoparticle-based optical materials.

Expeditious synthesis of functionalized tricyclic 4-spiro pyrano[2,3-c]pyrazoles in aqueous medium using dodecylbenzenesulphonic acid as a Brønsted acid–surfactant-combined catalyst

An efficient, three-component, one-pot synthesis of highly functionalized tricyclic 4-spiro pyrano[2,3-c]pyrazoles incorporating medicinally privileged heterocyclic moieties has been developed, which also involves the tandem Knoevenagel/Michael addition reaction followed by dehydrative cyclization of pyrazolone derivatives, cyclic 1,3-diketones and cyclic ketones, catalyzed by dodecylbenzenesulphonic acid (DBSA) as a Bronsted acid–surfactant-combined catalyst in aqueous medium. The catalyst is found to be highly competent in accelerating this reaction that results in a considerable short reaction time, alleviating the need for high thermal energy. Wide substrate scope, high to excellent product yield, operational simplicity, absence of any hazardous organic solvent, mild reaction conditions, a simple work up procedure and easily available starting materials are the salient features of this protocol.

Facile synthesis of functionalized 6-cyano-2-oxa-7-azabicyclo[4.1.0]hept-3-en-1-yl acetates: a catalyst free approach to access the pyran fused 2-acetoxy-NH-aziridines

Novel 6-cyano-2-oxa-7-azabicyclo[4.1.0]hept-3-en-1-yl acetate scaffolds were synthesized directly from 2-amino-3-cyano-4-H-pyrans as well as 2-amino-3-cyano-spiropyrans using iodobenzene diacetate (PIDA) as oxidant at room temperature in the absence of any catalyst. Essentially, the enamine fragment of the reactants reacts with PIDA, which makes this reaction a new way to synthesize pyran fused 2-acetoxy-NH-aziridines. These remarkably stable pyran fused 2-acetoxy-NH-aziridines can be used in SAR studies in pharmaceutical and medicinal chemistry. Ready availability of the starting materials, operational simplicity, absence of metal catalyst, mild reaction conditions, and simple workup procedure are the other significant features of this reaction.