Sandip K. Nayak

Surfactant-assisted porphyrin based hierarchical nano/micro assemblies and their efficient photocatalytic behavior.

In this report, we have demonstrated the synthesis of surfactant-assisted different morphologies of meso-tetra(4-carboxyphenyl)porphyrin assemblies (spherical to flower shaped). These nano/micro assemblies are well characterized by scanning electron microscopy and X-ray diffraction. The formation of assemblies is driven by noncovalent interactions such as hydrophobic-hydrophobic and aromatic π-π stacking between the molecules. The steady state and time-resolved spectroscopic investigation reveal that different assemblies are formed by virtue of special supramolecular organizations. The photocatalytic activities of different assemblies have been demonstrated with an organic pollutant Rhodamine B dye under the visible light irradiation. Such porphyrin based assemblies could pave the way for designing new optical based materials for the applications in photocatalytic, photovoltaic, and light harvesting system.

Low-valent titanium : A new approach to deprotection of allyl and benzyl groups

Abstract A novel method for the deprotection of allyl and benzyl derivatives of alcohols and phenols by low-valent titanium [Ti(O)] is reported. The possible mechanism is discussed.

Supramolecular Interaction of Coumarin 1 Dye with Cucurbit[7]uril as Host: Combined Experimental and Theoretical Study

Molecules of the coumarin family have fluorescence characteristics that are highly sensitive to their environment, and thus, they have been used as fluorescent sensors in chemical and biological systems. However, the very poor fluorescence yield of most coumarin dyes in aqueous media limits their applications. We have adopted a supramolecular strategy to improve the fluorescence intensity of coumarin dye through its interaction with the relatively new host cucurbit[7]uril (CB[7]). The virtually nonfluorescent coumarin 1 (Φ(f) = 0.04) was converted into a highly fluorescent (Φ(f) = 0.52) entity in water upon addition of the nonfluorescent host CB[7]. Various spectroscopy techniques, namely, UV-vis absorption and steady-state and time-resolved fluorescence spectroscopies, established the formation of a strong 1:1 dye-CB[7] inclusion complex with a high binding constant of (1.2 ± 0.1) × 10(5) M(-1) for the dye. The stable inclusion complex of the neutral molecule was supported by density-functional-theory- (DFT-) based quantum chemical calculations. Energy decomposition analysis of various interaction factors in the host-guest complex revealed that key components providing stability to the complex were electrostatic, polarization, and charge-transfer energies. These new results on the formation of a strong inclusion complex of the versatile fluorophore coumarin 1 with the nontoxic host CB[7] could lead to the design of efficient molecular-scale biological probes, sensors, and photostable aqueous UV dye lasers.

Enantioselective conjugate addition of diethylzinc to chalcones catalysed by N-trityl aziridine-2-(S)-(diphenyl)methanol and Ni(acac)2

Abstract The chiral Ni(II) complex prepared from Ni(acac) 2 and N -trityl aziridine-2-( S )-(diphenyl)methanol catalyses the enantioselective conjugate addition of diethylzinc to chalcones in good yield with ees of upto 93%.

Study of ground state EDA complex formation between [70]fullerene and a series of polynuclear aromatic hydrocarbons

[70]fullerene has been shown to form 1:1 EDA complex with anthracene, naphthalene, phenanthrene, pyrene and acenaphthene in CCl4 medium. Charge transfer (CT) bands have been detected in all the cases. Isosbestic points have been observed in the cases of phenanthrene and acenaphthene complexes. Ionisation potentials of the donors and CT transition energies have been found to correlate in accordance with Mulliken equation and from this correlation the electron affinity of C70 has been found to be 2.59 eV. Enthalpies and entropies of formation of the complexes have been estimated from the formation constants of the complexes determined spectrophotometrically at three different temperatures.

Slow Magnetic Relaxations in Manganese(III) Tetra(meta-fluorophenyl)porphyrin-tetracyanoethenide. Comparison with the Relative Single Chain Magnet ortho Compound

Mn(III) tetra(meta-fluorophenyl)porphyrin-tetracyanoethenide coordination polymer (abbreviated meta-F) was synthesized and crystallographically and magnetically characterized. The compound crystallizes in the space group C2/c with four equivalent molecules in the unit cell arranged along two symmetry related nonparallel linear chain directions. Magnetic properties were studied by SQUID dc magnetization and ac susceptibility techniques and high field-high frequency electron spin resonance (HF-ESR). Glassy transition to a ferromagnetic-like state is observed at 10 K accompanied by slow magnetic relaxations. The glassiness is interpreted as due to 3D domain wall pinning. In a bias dc magnetic field the width of the relaxation time distribution decreases and the relaxations become similar to the relaxations of the single chain magnet Mn(III) tetra(ortho-fluorophenyl)porphyrin-tetracyanoethenide (abbreviated ortho-F), for which comparative HF-ESR studies were also conducted in this work. Magnetic properties of these two compounds are compared, and the nature of magnetic relaxations in meta-F is discussed.

Copper(II) Bromide: A Simple and Selective Monobromination Reagent for Electron‐Rich Aromatic Compounds

Abstract Copper(II) bromide was found to be a simple and efficient reagent for monobromination of electron‐rich aromatic compounds at room temperature. The reaction proceeded smoothly with phenols, aryl alkyl ethers, and aromatic amines to afford the corresponding monobrominated product selectively in moderate to good yields.

Reductive dehydroxylation of Baylis–Hillman adducts with low-valent titanium reagent: syntheses of stereoselective trisubstituted alkenes

Abstract The Baylis–Hillman adducts prepared from aromatic aldehydes and methyl acrylate underwent smooth dehydroxylation with concomitant olefin isomerisation with low-valent titanium reagent to provide the trisubstituted alkenes with high (E)-selectivity.

Absorption spectroscopic study of EDA complexes of [70] fullerene with a series of methyl benzenes

[70]Fullerene has been shown to form 1:1 molecular complexes with toluene, p-xylene, m-xylene, 1,2,4,5-tetramethyl benzene (durene) and pentamethyl benzene (PMB) in CCl4 medium by absorption spectroscopic method. Isosbestic points have been detected in case of complexes with PMB and durene. Charge transfer absorption band could not be detected but the intensity of the broad absorption band of C70 in CCl4 decreases systematically with increase in the concentration of the added methylbenzenes. From this trend the formation constants (Kc) of the complexes have been determined at three different wavelengths. The constancy of Kc with respect to change in the wavelength of measurement supports the view that complex of a single stoichiometry (1:1) is formed in each case.

(±)-Camphor-10-sulfonic acid catalyzed direct one-pot three-component Mannich type reaction of alkyl (hetero)aryl ketones under solvent-free conditions: application to the synthesis of aminochromans

Direct three-component Mannich type reactions of (hetero)aromatic ketones with aromatic aldehydes and aromatic amines were efficiently catalyzed by camphor-10-sulfonic acid at ambient temperature under solvent free conditions to afford β-amino ketones in good to excellent yields. Syntheses of aminochromans were accomplished from one of the Mannich adducts via an unprecedented route involving intramolecular etherification with CuI/8-hydroxyquinoline.