Graphene oxide-controlled neutral versus cationic form of a red emitting dye: enhancement of fluorescence by graphene oxide.

Fluorescence enhancement of fluorophores in neat solvent media in the presence of graphene oxide (GO) is less known. It is necessary to re-examine the role of GO from the fundamental scientific viewpoint. Herein, we have reported GO controlled conversion from the neutral to cationic form of a red emitting molecule. Besides this, the switching of the role of GO as an enhancer to a quencher of fluorescence depending on the concentration of GO in the presence of proton accepting solvent media was established. Intermolecular proton transfer from the GO surface to fluorophores is responsible for this phenomenon.

Graphene Oxide as an Enhancer of Fluorescence.

Solvent-dependent switching of graphene oxide (GO) as fluorescence quencher or enhancer was observed. In some solvents, GO increases the fluorescence yield of a hydrophilic molecule 7-(diethylamino)-coumarin-3-carboxylic acid (7-DCA), and in some solvents GO act as a quencher of fluorescence.

Host-guest interaction of 3-hydroxyflavone and 7-hydroxyflavone with cucurbit [7]uril: A spectroscopic and calorimetric approach.

The modulation of photophysical behaviour of small organic molecules in the presence of macrocycles is one of the most interesting areas of research. In this work we reported the interaction of two biologically active molecules 3-hydroxyflavone and 7-hydroxyflavone with macrocyclic host cucurbit [7]uril in aqueous medium. To investigate the change of photophysical properties of these two flavones, we have used steady state absorption, fluorescence, time resolved fluorescence emission spectroscopy and isothermal titration calorimetric technique. It is observed that on complexation with cucurbit [7]uril, the excited state proton transfer processes in both flavones have been facilitated. Isothermal titration calorimetric method was used in order to investigate the involvement of thermodynamic parameters in complexation between flavone with cucurbit [7]uril. The changes in thermodynamic properties due to the complexation of the flavones molecules with cucurbit [7]urils help to understand about the governing parameters involved in this complexation. The inclusion of flavone molecules inside the cavity of cucurbit [7]uril molecules was studied theoretically to decipher the molecular orientation of flavones in the presence of cucurbit [7]uril. The structure of HOMO and LUMO of the complexes between cucurbit [7]uril with flavones was reported. This study will be helpful to get the knowledge about the modulation of photophysical properties of the flavones molecules on addition of macrocyclic host cucurbit [7]uril. This study will be helpful for the use of cucurbit [7]uril as a potential drug delivery system.

Heterotrimetallic compounds containing Mo-M-Li [M = K, Rb and Cs] clusters: synthesis, structure, bonding, aromaticity and theoretical investigations of Li2M2 [M = K and Rb] and Cs4 rings.

A new polydentate fac-trioxo molybdenum complex, [MoO(3)L](3-) {LH(3) = nitrilotriacetic acid}, has been synthesized by the reaction of lithium molybdate with iminodiacetic acid. The trinegative complex anion coordinates the alkali metal cations, K(+), Rb(+) or Cs(+). The potassium, rubidium and cesium complexes, [Li{K(H(2)O)(2)}MoO(3)L](n) (1), [Li{Rb(H(2)O)(2)}MoO(3)L](n) (2) and [Cs{Li(H(2)O)}(2)MoO(3)L](n) (3), form heterotrimetallic coordination chains, containing planar rings of Li(2)M(2) (M = K or Rb) and Cs(4). Theoretical investigations on these rings were carried out using NICS calculations and ab initio ring current maps, revealing aromaticity to be of limited significance.

Some novel molecular frameworks involving representative elements.

Several new molecular frameworks with interesting structures, based on clusters of main group elements have been studied at different levels of theory with various basis sets. Conceptual density functional theory based reactivity descriptors and nucleus independent chemical shift provide important insights into their bonding, reactivity, stability and aromaticity.

Understanding local electrophilicity/nucleophilicity activation through a single reactivity difference index.

A local reactivity difference index R(k) is shown to be able to predict the local electrophilic and/or nucleophilic activation within an organic molecule. Together with the electrophilic and/or nucleophilic behavior of the center k given by the sign, the magnitude of the R(k) index accounts for the extent of the electronic activation, a behavior that allows for the use of the R(k) index as a measure of the molecular reactivity especially in polar processes.

Aromaticity in all-metal annular systems: the counter-ion effect.

The effect of counterions on the bonding, stability and aromaticity of trigonal dianion metal clusters has been analyzed through the behavior of various conceptual density functional theory based reactivity descriptors and the nucleus independent chemical shift calculated at different levels of theory, comprising one-determinant approaches and beyond (QCISD, CASSCF(8,8) and NEVPT2), for a proper benchmarking. Although several important insights into the counter-ion effects are obtained, much needs to be done in order to have a transparent idea therein.

Bonding, aromaticity, and structure of trigonal dianion metal clusters.

Various isomers of the trigonal dianion metal clusters, X(3)(2-), X = Be, Mg, Ca, and their mono- and disodium complexes are optimized at the B3LYP/6-311+G(d) level. Different conceptual density functional theory based reactivity descriptors as well as the induced magnetic field values are calculated to understand the stability and aromaticity of these systems. Possibility of bond stretch isomerism is explored. Genetic algorithm results lend additional insights into the structures of these isomers.