The molecular diversity scope of 4-hydroxycoumarin in the synthesis of heterocyclic compounds via multicomponent reactions

Molecular Diversity - 4-Hydroxycoumarins are some of the most versatile heterocyclic scaffolds and are frequently applied in the synthesis of various organic compounds. 4-Hydroxycoumarin-based...     

Photoelectron spectra of 1,2-indandione, 1,3-indandione and heterocyclic analogues

The photoelectron (He(I)) spectra of 1,2-indandione and heteroanalogues (coumarandione, thionaphthenequinone, and isatin), 1,3-indandione and heteroana     

Recent advances in molecular diversity

Molecular Diversity -     

The impact of polystyrene resins in solid-phase organic synthesis

Summary A major objective of the DIVERSOMER^® technology is to provide pure and characterized compounds for biological testing in order to prevent false negatives in our libraries. On several occasions, analysis of the final products by¹H-NMR and MS, has revealed by-products from the polystyrene solid support. Subsequently, three alternative methods were studied to remove polystyrene by-products; (i) prewashing of the resin prior to execution of the synthesis; (ii) pretreatment of the resin with the cleavage conditions consistent with the solid-phase synthesis reaction scheme; and (iii) parallel purification.     

On the industrial applications of MCRs: molecular diversity in drug discovery and generic drug synthesis

During the last decades, multicomponent chemistry has gained much attention in pharmaceutical research, especially in the context of lead finding and optimization. Here, in particular, the main advantages of multicomponent reactions (MCRs) like ease of automation and high diversity generation were utilized. In consequence of these beneficial properties, a plethora of new MCRs combined with appropriate classical reaction sequences have been published, the accessible chemical space was extended steadily. In the meantime, the desired high diversity became a challenge itself, because by now the systematic use of this huge and unmanageable space for drug discovery was limited by the lack of suitable computational tools. Therefore, this article provides an insight for the rational use of this enormous chemical space in drug discovery and generic drug synthesis. In this context, a short overview of the applied chemo informatics, necessary for the virtual screening of the biggest available chemical space, is given. Furthermore, some examples for recently developed multicomponent sequences are presented.     

The molecular structure and intermolecular interactions of 1,3:2,4-dibenzylidene-D-sorbitol

The 1,3(R):2,4(S)-dibenzylidene-D-sorbitol (DBS) molecule is a low molar mass organic gelator (LMOG) that is capable of hydrogen-bonding with itself. As a consequence, DBS molecules self-organize into nanofibrillar networks at relatively low concentrations in a wide variety of organic solvents and polymers. In this work, molecular mechanics and molecular dynamics simulations were conducted to elucidate the equilibrium structure of DBS and the molecular interactions that govern DBS self-assembly. Molecular mechanics calculations performed on single DBS molecules with Cerius² and InsightII software reveal that the pheny^l rings tend to adopt an equatorial position and that the pendant hydroxyl group prefers to form an intramolecular hydrogen bond with an acetal oxygen, in contrast to the terminal hydroxyl group. Molecular mechanics and molecular dynamics on DBS dimers reveal that they are capable of forming hydrogen bonds and participating in π interactions, suggesting that the mechanism of nanofibrillar network formation may be complex, involving more than one type of physical interaction.     

Singlet triplet-triplet-triexcitons in organic molecular crystals

A theory on the formation of triexcitons consisting of one singlet exciton and two triplet excitons is developed by considering exciton-exciton dynamical interactions. The conditions for the existence of the singlet-triplet-triplet-triexciton bound states are established and discussed.     

Progress in molecular organic electroluminescent materials

Efficient electroluminescence from sublimated organic films at low voltage was first reported in 1987. Since then, an important volume of academic and industrial research has been realized in order to develop new efficient materials with high life time but also to optimize the technological steps of the devices fabrication. So, in this paper, the best known materials to date are described.     

New synthesis of multi-walled carbon nanotubes using an arc discharge technique under organic molecular atmospheres

We have synthesized multi-walled carbon nanotubes (MWNTs) using a DC arc discharge method under organic molecular atmospheres. This method allows us to synthesize about five times more MWNTs than are synthesized using the usual arc discharge method, using discharge conditions of 100 A and 20 V. We have examined the synthetic yield of MWNTs at various pressures under different organic atmospheres. The yield of MWNTs increases with the number of carbon atoms in the organic molecule. Received: 21 September 2000 / Accepted: 18 December 2000 / Published online: 26 April 2001     

Origin of delocalization in organic molecular conductors

The delocalization of electron states in one-dimensional metals, such as TTF-TCNQ, accounts for the observed itinerant motion of the electrons at temperatures above about 50 K. This delocalization is related to the extended nature of the molecules in organic metals, which causes the amplitude for forward scattering by the phonons to exceed the amplitude for backward scattering by an order of magnitude. The large forward scattering, which delocalizes the electrons, does not contribute to the resistivity in the delocalized state.     

Recent advances in high-pressure organic synthesis

Abstract

The effect of pressure on several types of organic reactions, important from the synthetic point of view, is described in order to illustrate the present situation and prospects of high-pressure techniques in organic synthesis.

Les effets de la pression sur divers types de reactions organiques importantes en synthese, sont etudies afin de donner quelques illustrations de I'etat actuel des connaissances, et d'evaluer I'evolution future des techniques et leurs applications synthetiques.     

Charged Frenkel biexcitons in organic molecular crystals

It is known that the energy of the lowest electronic transition in the neutral molecules of anthracene, tetracene, and other polyacenes is blue-shifted in comparison with the corresponding transition energy in univalent molecular ions. This effect in a molecular crystal may be responsible for the attraction between a molecular (Frenkel) exciton and a charge carrier. Due to this attraction, a bound state of Frenkel exciton and free charge (charged Frenkel exciton) may be formed [5]. As we demonstrate below, the same mechanism can be responsible for the formation of a charged biexciton (bound state of two Frenkel excitons and a charge carrier). A one-dimensional lattice model is used which corresponds to J aggregates and is also a good approximation for quasi-one-dimensional crystals. Calculations are performed for molecular crystals like tetracene, where the exciton band at low temperature is much narrower than the band of the charge carrier.     

Directed photocurrent in Langmuir-Schaefer organic molecular films

In the three-layer Langmuir-Schaefer films consisting of a monolayer of donor-acceptor phtalocyanine-fullerene dyad molecules (Bu ₃ ProM ₂ F) and two layers of poly(3-hexylthiophene) (PHT), placed into an electrochemical cell, the electric current resulted from optical excitation of sampleswas measured with no external voltage source. Samples were excited by the xenon lamp light passed through amonochromator or by a source simulating the solar spectrum. It was shown that the current density in samples reached 40–50 µA/cm² in the latter case. Current-voltage characteristics of samples were measured. Photovoltaic responses of three-layer structures were studied by the time-resolved Maxwell displacement charge method. The preferred orientation of dyad molecules in the film was demonstrated.     

Ultrafast relaxation in quasi-one-dimensional organic molecular crystals

We present a comprehensive study of ultrafast relaxation properties of optical excitations in thin films of quasi-1D stacked organic materials PTCDA (3,4,9,10-perylenetetracarboxylic dianhydride) and MePTCDI (N,N'-dimethylperylene-3,4,9,10-dicarboximide) over five decades of time. Pump-probe experiments reveal excitonic intraband relaxation time constants of 65 fs for MePTCDI and 100 fs for PTCDA. The initial time-resolved luminescence anisotropy is consistent with the exciton model of Davydov-split states. The subsequent decay of the anisotropy can be explained with a thermally activated exciton hopping process. A full understanding of the pump-probe experiments calls for an explanation beyond the models presently available.     

Incoherent singlet-triplet biexcitons in organic molecular crystals

The conditions of the existence, the energy spectrum of internal motion and the dynamics of propagation as a whole of incoherent singlet-triplet biexcitons in organic molecular crystals is studied theoretically. It is assumed that the group velocity of the propagation of singlet excitons is very high with respect to that of triplet excitons.     

Transformation of charge transfer excitons into molecular excitons in molecular organic crystals

Formulae for persec probabilities of the nonradiative and radiative transformation of charge transfer excitons into molecular excitons in molecular organic crystals are derived and discussed. Numerical calculations are performed for solid naphtalene and anthracene.