Search results for "Intramolecular force"
showing 10 items of 599 documents
A theoretical study of the intramolecular charge transfer in 4-(dimethylamino)benzethyne
2014
We have investigated the non-adiabatic relaxation processes occurring in the singlet manifold of 4-(dimethylamino)benzethyne (DMABE){,} a molecule isoelectronic with 4-(dimethylamino)benzonitrile (DMABN) but lacking its characteristic dual fluorescence{,} using multireference perturbation theory methods. The results obtained point out to the existence of a two-fold decay mechanism in which the population of the initially accessed La state bifurcates towards a locally excited (LE) and a [small pi][sigma]* state. Further relaxation to an emitting intramolecular charge transfer (ICT) state is impeded due to the presence of pronounced energy barriers along their associated potential energy surf…
Synthesis, structure and photophysical properties of a highly luminescent terpyridine-diphenylacetylene hybrid fluorophore and its metal complexes
2014
A new fluorescent terpyridyl-diphenylacetylene hybrid fluorophore 4'-[4-{(4-methoxyphenyl)ethynyl}phenyl]-2,2':6',2''-terpyridine, L, was synthesized via Sonogashira cross-coupling of 4'-(4-bromophenyl)-2,2':6',2''-terpyridine and 4-ethynylanisole in the presence of Pd(PPh3)4/CuI as a catalyst. The solid state structure of L shows a trans arrangement of pyridine nitrogen atoms along the interannular bond in the terpyridine domain. Five transition metal complexes of L, {[FeL2](CF3SO3)2 (1), [ZnL2](ClO4)2 (2), [CdL2](ClO4)2 (3), [RuL2](PF6)2 (4), and PtMe3IL (5)}, have also been synthesized and characterized by spectroscopic methods and single crystal X-ray analysis. The X-ray crystal structu…
Communication between iron(II) building blocks in cooperative spin transition phenomena
2003
[EN] In the present article we discuss the cooperative nature of the spin crossover phenomenon in iron(II) complexes, providing a perspective of the state of the art in this area. The first aspect we discuss is the role of the intermolecular interactions, more precisely the ¿-interactions, in mononuclear complexes. We show that by playing with the nature of the ligands, aliphatic, aromatic, or extended aromatic, it is possible to create stronger cohesive forces and receive a more cooperative response from the compound. In the next step the singular family of bipyrimidine-bridged iron(II) dinuclear compounds is presented as the simplest example of polynuclear spin crossover complexes exhibit…
Light-induced, site-selective isomerization of glyoxylic acid in solid xenon
2014
Abstract The isomerization of glyoxylic acid (GA) and its water complex was studied in a low temperature xenon matrix. The aim of these studies was to understand how xenon environment affects the cis-trans GA interconversion upon near infrared irradiation. In solid xenon, the GA conformers are embedded in two different matrix sites. These show up as different vibrational bands of GA that exhibit different kinetic rates of isomerization. Upon complexation with water, the isomerization process slows down. Xenon matrix appears not to affect energy relaxation process via intramolecular or intermolecular hydrogen bond as compared with previous experiments in an argon.
Azonia spiro polyaza macrocycles containing biphenyl subunits as anion and cation receptors
2011
Abstract The reaction of N-Boc triprotected cyclam with bis(chloromethyl)biphenyl followed by the corresponding deprotection of the nitrogen atoms allows the preparation of receptor 3 containing an azonia spiro subunit. This receptor shows slightly increased basicity than cyclam, in particular for the formation of the appropriate triply charged species as a consequence of the reduced capacity of the structure present in 3 to stabilize the species with lower protonation degrees through the formation of intramolecular hydrogen bonds. The properties of 3 as a receptor for Cu2+ and Zn2+ and the anions derived from PO 4 3 − ( Pi ) , P 2 O 7 4 − ( PPi ) , P 3 O 10 5 − ( TPP ) and ATP have been st…
Pressure- and temperature-induced valence tautomeric interconversion in a o-dioxolene adduct of a cobalt-tetraazamacrocycle complex
2001
An electronic switch at the molecular level has been realized by using a class of ionic compounds of the formula [Co(L)(diox)]Y (L = tetraazamacrocyclic ligand, Y = mononegative anion). Such compounds undergo temperature- and pressure-induced intramolecular one-electron transfer equilibria. The transition temperature of interconversion varies with the nature of the counterions Y (Y = PF6, BPh4, I). Surprisingly the effect of the anion on the transition temperature is not only governed by its volume but also by its coulombic interaction.
Can the absence of solvation of neutral reagents by ionic liquids be responsible for the high reactivity in base-assisted intramolecular nucleophilic…
2005
[reaction: see text] The kinetics of the rearrangement of the Z-phenylhydrazone of 3-benzoyl-5-phenyl-1,2,4-oxadiazole (1a) into the relevant 4-benzoylamino-2,5-diphenyl-1,2,3-triazole (2a) induced by amines have been studied in two room-temperature ionic liquids (IL-1, [BMIM][BF4] and IL-2, [BMIM][PF6]). The data collected show that the reaction occurs faster in ionic liquids than in other conventional solvents previously studied (both polar or apolar, protic or aprotic). Presumably, this could depend on their peculiar ability to minimize the strong substrate-solvent, amine-solvent and amine-amine interactions occurring in conventional solvents.
Convergent results from experimental and theoretical DFT studies of the intramolecular rearrangement of Z-hydrazones of 3-acetyl-1,2,4-oxadiazoles
2004
A combined kinetic and theoretical study of the monocyclic rearrangements of heterocycles (MRH) has been carried out. The interconversion of the Z-hydrazone of 3-benzoyl-5-phenyl-1,2,4-oxadiazole into the corresponding triazole has been experimentally investigated in dioxane/water in the pS(+) range 5.5(5)-13.9. The uncatalyzed region has been examined at the DFT level using a model system formed by the Z-hydrazone of 3-formyl-1,2,4-oxadiazole and one or two water molecules. The environmental effect of the solvent has been emulated using a continuum model (COSMO) approach. The kinetic data suggest a concerted process where the magnitude of the activation barrier is determined by the interpl…
Structural analysis of two foldamer-type oligoamides – the effect of hydrogen bonding on solvate formation, crystal structures and molecular conforma…
2012
Author's Final draft The crystal structures and molecular conformations of two foldamer-type oligoamides were analyzed. One polymorphic form and seven solvates were found for N¹,N³-bis(2-benzamidophenyl)benzene-1,3-dicarboxamide (the benzene variant), and two polymorphic forms and six solvates for N²,N⁶-bis(2-benzamidophenyl)pyridine-2,6-dicarboxamide (the pyridine variant). Three crystal structures of the benzene variant and seven structures of the pyridine variant were solved using single crystal X-ray diffraction. The crystal structures showed that the different modes of intramolecular hydrogen bonding strongly affect the conformation and folding of the molecules, which is most evidently…
Synthesis of pyrazole-4-carbohydrazide derivatives of pharmaceutical interest
2003
New 1-phenylor 1-methyl-5-benzamidopyrazole-4-carbohydrazide derivatives were prepared in 70–90% yields from 1-methylor 1-phenyl-6-phenylpyrazolo[3,4-d]1,3-oxazin-4(1H)-one derivatives and hydrazine hydrate. Small quantities of the isomeric 5-aminopyrazole-4-(Nbenzoyl)hydrazides were detected in some reaction mixtures, proving that intramolecular benzoyl migration can take place in the 5-benzamidopyrazole-4-carbohydrazide molecule. The direct formation of pyrazole-4-carbohydrazides from 5-benzamidopyrazole-4-carboxylic acid ethyl esters and hydrazine hydrate was unsuccessful.