Indian Association for the Cultivation of Science

About: Indian Association for the Cultivation of Science is a education organization based out in Kolkata, India. It is known for research contribution in the topics: Excited state & Catalysis. The organization has 3867 authors who have published 10457 publications receiving 220098 citations.

Aligned 1-D nanorods of a π-gelator exhibit molecular orientation and excitation energy transport different from entangled fiber networks

Abstract: Linear π-gelators self-assemble into entangled fibers in which the molecules are arranged perpendicular to the fiber long axis. However, orientation of gelator molecules in a direction parallel to the long axes of the one-dimensional (1-D) structures remains challenging. Herein we demonstrate that, at the air–water interface, an oligo(p-phenylenevinylene)-derived π-gelator forms aligned nanorods of 340 ± 120 nm length and 34 ± 5 nm width, in which the gelator molecules are reoriented parallel to the long axis of the rods. The orientation change of the molecules results in distinct excited-state properties upon local photoexcitation, as evidenced by near-field scanning optical microscopy. A detailed understanding of the mechanism by which excitation energy migrates through these 1-D molecular assemblies might help in the design of supramolecular structures with improved charge-transport properties.

Correlation of Dopant States and Host Bandgap in Dual-Doped Semiconductor Nanocrystals

Abstract: Excitation of a semiconductor nanocrystal generates an electron–hole pair, which on recombination results in band edge excitonic emission. Insertion of impurity or dopant state capable of donating and/or accepting electrons can change the recombination process and leads to new emission called dopant emission. However, the presence of more than one impurity state generates multiple recombination possibilities, and the allowed transition might follow selective, additive, or a new path to get a new emission. To understand this, herein we report the correlation of host bandgap with dopant states in different dual-doped semiconductor nanocrystals. This has been achieved by doping two optically active (Mn and Cu) dopants in one semiconducting nanocrystal and observing the dopant emission changes with continuous variation of host bandgap. It has been observed that Mn d-state emission is predominated in dual-doped ZnS and Cu impurity state emission for ZnSe in spite of presence of both Mn and Cu in each semicondu...

Nanoparticle Multivalency Directed Shifting of Cellular Uptake Mechanism

Abstract: Although nanoparticle multivalency is known to influence their biological labeling performance, the functional role of multivalency is largely unexplored. Here we show that the folate receptor mediated cellular internalization mechanism of 35–50 nm nanoparticle shifts from caveolae- to clathrin-mediated endocytosis as the nanoparticle multivalency increases from 10 to 40 and results in the difference of their subcellular trafficking. We have synthesized folate functionalized multivalent quantum dot (QD) with varied average numbers of folate per QD between 10 and 110 [e.g., QD(folate)10, QD(folate)20, QD(folate)40, QD(folate)110] and investigated their uptake and localization into folate receptor overexpressed HeLa and KB cells. We found that uptake of QD(folate)10 occurs predominantly via caveolae-mediated endocytosis and entirely trafficked to the perinuclear region. In contrast, uptake of QD(folate)20 occurs via both caveolae- and chathrin-mediated endocytosis; uptake of QD(folate)40 and QD(folate)110 o...

Search for a stable alignment limit in two-Higgs-doublet models

Abstract: We study the conditions required to make the two-Higgs-doublet-model (2HDM) scalar potential stable up to the Planck scale. The lightest $CP$-even scalar is assumed to have been found at the LHC and the alignment limit is imposed in view of the LHC Higgs data. We find that ensuring stability up to scales $\ensuremath{\gtrsim}1{0}^{10}\text{ }\text{ }\mathrm{GeV}$ necessitates the introduction of a soft breaking parameter in the theory. Even then, some interesting correlations between the nonstandard masses and the soft breaking parameter need to be satisfied. Consequently, a 2HDM becomes completely determined by only two nonstandard parameters, namely, $\mathrm{tan}\ensuremath{\beta}$ and a mass parameter, ${m}_{0}$, with $\mathrm{tan}\ensuremath{\beta}\ensuremath{\gtrsim}3$. These observations make a 2HDM, in the stable alignment limit, more predictive than ever.

Azo anion radical complexes of osmium and related nonradical species.

Abstract: The reaction of [Os(H)(Br)(CO)(PPh3)3], 5, with 2-(phenylazo)pyridine (pap) in boiling dry heptane has afforded the azo anion radical complex [Os(pap•-)(Br)(CO)(PPh3)2], 6a, as the major product and [Os(pap)(H)(CO)(PPh3)2]Br, 7, as a minor byproduct. Upon replacing pap by the better π-acceptor azo-2,2‘-bipyridine (abp) in the above synthesis, the radical complex [Os(abp•-)(Br)(CO)(PPh3)2], 6b, becomes the sole product. It is proposed that 6 is formed via homolytic cleavage of the Os−H bond in 5; in the formation of 7, the Os−Br bond of 5 is heterolytically cleaved. The X-ray structures of 6b and 7·CH2Cl2 have been determined. In 6b, the N−N length is 1.35(2) A, consistent with the anion radical description; in 7·CH2Cl2 the length is 1.27(1) A. The spin-bearing extended Huckel HOMO in a model of 6 is found to be ∼70% azo-π* in character associated with a small metal contribution. An electronic band observed in the range 600−700 nm in solutions of 6 is assigned to the HOMO → LUMO transition, the LUMO being ...