Search results for "force"
showing 10 items of 3423 documents
Relatively strong intramolecular antiferromagnetic coupling in a neutral Cr(III)2Nb(V)2 heterobimetallic molecular square.
2015
A relatively large antiferromagnetic interaction between the two chromium(III) ions from the molecular square [{Cr(dmso)4}2{Nb(μ-O)2(C2O4)2}2] () (J = -12.0 cm(-1)) is mediated by the diamagnetic oxo-Nb(V)-oxo pathway, its nature and magnitude being substantiated by DFT type theoretical calculations.
Molecular structure of p -methylaniline and its van der Waals complexes with CF 3 H, CH 4 and CF 4 studied by laser induced fluorescence spectroscopy…
2002
The UV fluorescence excitation and dispersed fluorescence spectra of jet-cooled p-methylaniline have been obtained for the S1←S0 transition. The main spectral bands have been assigned by comparison with those of other relevant substituted benzenes and with the help of computed vibrational frequencies. The structure of p-methylaniline in both the S0 and S1 states has been studied at ab initio quantum chemical calculations at MP2 and CIS levels of theory using the 6-31+G∗ basis sets. Both low- and high-resolution laser induced fluorescence spectra of p-methylaniline van der Waals complexes with CF3H, CH4 and CF4 have been characterised following jet-expansion investigations. The equilibrium g…
Extension of Conjugation Leading to Bathochromic or Hypsochromic Effects in OPV Series
2004
Four OPV series 1-4 (a-d) with a terminal dialkylamino group as electron donor were prepared by Wittig-Horner reactions. To study the influence of the push-pull effect on the long-wavelength absorption, three of the four series contained terminal acceptor groups (CN, CHO, NO(2)). The length of the chromophores strongly affects the intramolecular charge transfer (ICT)-an effect which superimposes upon the extension of the conjugation. Increasing numbers n of repeat units cause an overall bathochromic shift for the purely donor-substituted series 1 a-4 a and the series 1 b-4 b with CN as weak acceptor. The two effects annihilate each other in the series 1 c-4 c with terminal CHO groups, so th…
Crystalline self-assembly induced by aromatic edge-to-face interactions: the crystal structure of 2,6,6,10-tetrabenzyl-2,10-diaza-6-azonia[11]paracyc…
2002
The crystal structure of 2,6,6,10-tetrabenzyl-2,10-diaza-6-azonia[11]paracyclophane bromide reveals several intermolecular aromatic edge-to-face interactions which are important in the three-dimensional growing of the crystalline structure. Molecular dynamics and semiempirical studies indicate that the conformer found in the crystal is not the most stable in solution confirming the important role that edge-to-face interactions play in the structural arrangement found in the solid state.
Reactivity and Selectivity of Ortho-Metalated Rhodium(II) Complexes in C−H Insertion Reactions of α-Diazo Compounds
1998
Regioselective intramolecular C−H insertion reactions of α-diazo β-keto esters and α-diazo ketones are mediated by Rh2[OOCR]4-x[PC]x (x = 1, 2; PC = ortho-metalated phosphine; R = CH3, C3F7). In particular, the intramolecular transformation of 1-diazo-5-methyl-3-propyl-2-hexanone catalyzed by Rh2[OOCCH3]2[PC]2 (PC = (C6H4)P(C6H5)2, head-to-tail (H−T) configuration) afforded only the tertiary C−H insertion product. By comparison, no C−H insertion reaction was promoted by doubly metalated complexes with a head-to-head (H−H) configuration. Rh2[OOCR]3[PC] compounds were found to be less suited for these type of reactions.
Breaking the semi-quinoid structure: spin-switching from strongly coupled singlet to polarized triplet state.
2014
2,7-TMPNO (4,5,9,10-tetramethoxypyrene-2,7-bis(tert-butylnitroxide)) was found to exist in semi-quinoid form with unprecedented strong intramolecular magnetic exchange interaction of 2 J/kB = 1185 K operating over a distance of 10 A. Structural transformations with the activation energy of ΔEeq = 949 K were observed by varying the temperature, from more quinoid structure at low temperature to more biradicaloid structure at higher temperature. Moreover, this molecule undergoes a transient spin transition from singlet to polarized triplet state upon photoexcitation revealed by TREPR spectroscopy. The spin Hamiltonian parameters were determined to be S = 1, g = 2.0065, D = -0.0112 cm(-1), and …
Raman and theoretical study of the solvent effects on the sizable intramolecular charge transfer in the push-pull 5-(dimethylamino)-5'-nitro-2,2'-bit…
2006
In this paper, we analyze the degree of intramolecular charge transfer in a push-pull π-conjugated system, 5-(dimethylamino)-5'-nitro-2,2'-bithiophene, from changes in frequencies and relative intensities of its strongestRaman scatterings in a bunch of solvents with different polarities. Density functional theory (DFT) was used as a support of the experimental study. Solvent effects on the molecular and electronic structures and on the vibrational properties were estimated by performing B3LYP/6-31G** calculations within the framework of the polarized continuum model (PCM) developed by Tomasi. Calculations reveal that the molecule is highly polarized in the ground state and behaves as a very…
Photoinduced phenomena in corona poled polar organic films.
2005
Abstract Organic materials have received considerable attention because of their large dipole moments and optical nonlinearities. The optically induced switching of material properties is important for studying the optoelectronic effects including second harmonic generation. Organic materials for photonic applications contain chromophore dipole which consist of acceptor and donor groups bridged by a delocalized π-electron system. Both theoretical and experimental data show a reversible highly dipolar photoinduced intra molecular charge transfer in betaine type molecules accompanied by change of the sign and the value of the dipole moment. The arrangement of polar molecules in films is studi…
Ion motion in salt water flowing under a transverse magnetic field
2012
The problem of ion motion in an electrolyte solution flowing in a thin rectangular duct with velocity VE in the presence of a transverse magnetic field B0 is studied by means of classical mechanics and electrodynamics. Because of Lorentz force on the ions in the electrolyte solution, a so called Faraday voltage appears at the electrodes orthogonal to both the field B0 and the velocity VE. The dynamics of positive and negative ions (cations and anions, respectively) in this classical system is studied by taking into account the viscosity of the fluid and the process of charge accumulation on the opposite walls of the duct. Hydrogen production is seen to take place at one of the electrodes wh…
Localized excitation effect on dipole moments of oligophenylenevinylenes in their excited Franck–Condon state
2010
Abstract The results from electrooptical absorption measurements (EOAM) on the ground and excited Franck–Condon state dipole moments of oligophenylenevinylenes in 1,4-dioxane and cyclohexane are presented. The dipole moments of quadrupolar dyes in the ground state are not equal zero. This means that one of the functional end groups of these molecules is not on the axis or on the plane with the central part of the molecule. Such a conclusion is confirmed by the quantum-chemical and semi-empirical recalculations. Owing to disorder in the ground-state geometry of the dyes the π–π conjugated system is located on mostly the plane part of the molecule and in the main this part absorbs the light. …