Synthesis of several series of liquid crystalline polyaroyl-bis-oxyarylates and their structure-property relationships

Several series of liquid crystalline polyaroyl-bis-oxyarylates containing 1,4-phenylene, 4,4'-biphenylene and 2,6-naphthylene units have been synthesized with the use of aroyl-bis-oxyaroyl dichlorides. Melting and clearing temperatures of every polymer under investigation were compared with those of corresponding polyterephthaloyl-bis-4-oxybenzoates.     

Synthesis of several series of liquid crystalline polyaroyl-bis-oxyarylates and their structure-property relationships

Abstract

Several series of liquid crystalline polyaroyl-bis-oxyarylates containing 1,4-phenylene, 4,4′-biphenylene and 2,6-naphthylene units have been synthesized with the use of aroyl-bis-oxyaroyl dichlorides. Melting and clearing temperatures of every polymer under investigation were compared with those of corresponding polyterephthaloyl-bis-4-oxybenzoates.     

Spectroscopic characterization of a series of platinum acetylide complexes having a localized triplet exciton

In this work, we describe the spectroscopic properties of a series of platinum complexes containing one acetylide ligand per platinum, having the chemical formula trans-Pt(PBu(3))(2)((C[triple bond]CC(6)H(4))(n)()-H)Cl, n = 1-3 (designated as half-PEn-Pt) and compare their spectroscopic behavior with the well-characterized series trans-Pt(PBu(3))(2)((C[triple bond]CC(6)H(4))(n)-H)(2), n = 1-3 (designated as PEn-Pt). This comparison aims to determine if the triplet state of PEn-Pt is confined to one ligand or delocalized across the central platinum atom. We measured ground-state absorption spectra, fluorescence spectra, phosphorescence spectra, and triplet-state absorption spectra. The ground-state absorption spectra and fluorescence spectra both showed a blue shift when comparing half-PEn-Pt with PEn-Pt, showing the S(1) state is delocalized across the platinum. In contrast, the phosphorescence spectra of the two types of compounds had the same 0-0 band energy, showing the T(1) state was confined to one ligand in PEn-Pt. The triplet state absorption spectra blue shifted when comparing half-PEn-Pt with PEn-Pt, showing the T(n) state was delocalized across the central platinum. This comparison supports recently published work that suggested this confinement effect (Rogers, J. E et al. J. Chem. Phys. 2005, 122, 214701).     

Impact of regularity in structure-property relationships

The regular evolution of properties with structural modification is quantitatively formulated. It is defined in a structural space which is exhaustive, ordered, flexible and explicit. It is detected along the ordered pathways of structural filiations by inference tools, which take into account the experimental precision and proceed by a heuristic modulation of the initial representation space. The introduction of nuances in the quantitative formulation of regularity leads to diverse tools for setting up and exploiting the relationships. These latter constitute a prediction law, which is both simple and as precise as the measurements. The detected regularities make for a generalization of certain structural effects and suggest a fruitful interpretation. Zeroth- and first-order regularities, characteristic of strongly linear variation, are used to safely extrapolate the prediction range and to orient experimental planning.     

Excited-state absorption properties of platinum(II) terpyridyl acetylides

A comprehensive photophysical study is presented which compares the ground- and excited-state properties of four platinum(II) terpyridyl acetylide compounds of the general formula [Pt(tBu3tpy)(CCR)]+, where tBu3tpy is 4,4',4' '-tri-tert-butyl-2,2':6',2' '-terpyridine and R is an alkyl or aryl group. [Ru(tBu3tpy)3]2+ and the pivotal synthetic precursor [Pt(tBu3tpy)Cl]+ were also investigated in the current work. The latter two complexes possess short excited-state lifetimes and were investigated using ultrafast spectrometry while the other four compounds were evaluated using conventional nanosecond transient-absorption spectroscopy. The original intention of this study was to comprehend the nature of the impressive excited-state absorptions that emanate from this class of transition-metal chromophores. Transient-absorbance-difference spectra across the series contain the same salient features, which are modulated only slightly in wavelength and markedly in intensity as a function of the appended acetylide ligand. More intense absorption transients are observed in the arylacetylide structures relative to those bearing an alkylacetylide, consistent with transitions coupled to the pi system of the ancillary ligand. Reductive spectroelectrochemical measurements successfully generated the electronic spectrum of the tBu3tpy radical anion in all six complexes at room temperature. These measurements confirm that electronic absorptions associated with the tBu3tpy radical anion simply do not account for the intense optical transitions observed in the excited state of the Pt(II) chromophores. Transient-trapping experiments using the spectroscopically silent reductive quencher DABCO clearly demonstrate the loss of most transient-absorption features in the acetylide complexes throughout the UV, visible, and near-IR regions following bimolecular excited-state electron transfer, suggesting that these features are strongly tied to the photogenerated hole which is delocalized across the Pt center and the ancillary acetylide ligand.     

Synthesis and structure-property relationships of amphiphilic organogelators

A series of low-molecular-weight amphiphilic molecules was synthesized and investigated for their ability to gel organic solvents. These amphiphilic molecules are composed of a head-group moiety capable of forming intermolecular associations through hydrogen bonds and n-alkyl chains of various lengths. This paper describes the continuation of recently published work, in which this class of gelators was presented for the first time. Here, the focus addresses systematically three different structural variations of the head-group moiety: 1) the rigidity, 2) the type and strength of the hydrogen-bond-forming units, and 3) the reduction of the intermolecular interaction by incorporating a lateral substituent. The gelation behavior was investigated in p-xylene and in several polar solvents. The aim was to establish structure-property relationships and to provide organogelators capable of forming gels at low concentrations with adjustable sol-gel transition temperatures and good optical quality. For some individual compounds of the series this property profile was achieved. For the investigated solvents, with particular compounds, sol-gel transition temperatures above 100 degrees C with a reasonable concentration of gelator are obtainable.     

Variable connectivity index as a tool for modeling structure-property relationships

We report on the calculation of normal boiling points for a series of n = 58 aliphatic alcohols using the variable connectivity index in which variables x and y are used to modify the weights on carbon (x) and oxygen atoms (y) in molecular graphs, respectively. The optimal regressions are found for x = 0.80 and y = -0.90. Comparison is made with available regressions on the same data reported previously in the literature. A refinement of the model was considered by introducing different weights for primary, secondary, tertiary, and quaternary carbon atoms. The standard error in the case of the normal boiling points of alcohols was slightly reduced with optimal weights for different carbon atoms from s = 4.1 degrees C (when all carbon atoms were treated as alike) to s = 3.9 degrees C.     

Ligand effects on charge transport in platinum(II) acetylides

To investigate the electrical characteristics of organometallic complexes as molecular conductors, organometallic pi-conjugated molecules of the type trans-[PtL2(CCC6H4SAc-4)2], where L = PCy3, PBu3, PPh3, P(OEt)3, P(OPh)3, were synthesized and characterized by NMR, IR, UV, and X-ray spectroscopies. For the three complexes (L = PCy3, PPh3, and P(OEt)3) that could be measured using a cross-wire junction technique, the current-voltage (I-V) characteristics of a molecular monolayer of these complexes showed no ligand effect, despite spectroscopic evidence that electronic interaction between the phosphine ligands and the pi-system does occur. It was concluded that the tunneling efficiency across the molecule is the determining factor for conduction in this metal-molecule-metal system. It was also shown that the incorporation of a transition metal in pi-conjugated molecular wires does not adversely affect charge transport compared to all-carbon pi-conjugated molecular wires.     

Interpretation of quantitative structure-property and -activity relationships.

The potential utility of data reduction methods (e.g. principal component analysis) for the analysis of matrices assembled from the related properties of large sets of compounds is discussed by reference to results obtained from solvent polarity scales, ongoing work on solubilities and sweetness properties, and proposed general treatments of toxicities and gas chromatographic retention indices.     

Synthesis, fluorescence, and two-photon absorption of a series of elongated rodlike and banana-shaped quadrupolar fluorophores: a comprehensive study of structure-property relationships

An extensive series of push-push and pull-pull derivatives was prepared from the symmetrical functionalization of an ambivalent core with conjugated rods made from arylene-vinylene or arylene-ethynylene building blocks, bearing different acceptor or donor end-groups. Their absorption and photoluminescence, as well as their two-photon-absorption (TPA) properties in the near infrared (NIR) region, were systematically investigated to derive structure-property relationships and to lay the guidelines for both spectral tuning and amplification of molecular TPA in the target region. Whatever the nature of the core or of the connectors, push-push systems were found to be more efficient than pull-pull systems, and planarization of the core (fluorene versus biphenyl) always leads to an increase in the TPA cross sections. In contrast, increasing the conjugation length as well as replacement of a phenylene moiety by a thienylene moiety in the conjugated rods did not necessarily lead to increased TPA responses. The present study also demonstrated that the topology of the conjugated rods can dramatically influence the TPA properties. This is of particular interest in terms of molecular engineering for specific applications, as both TPA properties and photoluminescence characteristics can be considerably affected. Thus, it becomes possible to optimize the transparency/TPA and fluorescence/TPA efficiency trade-offs for optical limiting in the red-NIR region (700-900 nm) and for two-photon-excited fluorescence (TPEF) microscopy applications, respectively.     

Quantitative structure-property relationships in the series of diazonium cations, intermediate products in the synthesis of analytical forms and dyes

It was demonstrated that the reduction potentials, dimerization potentials, and half-equivalence point potentials in the titration of aryldiazonium cations XC₆H₄N⁺N are linearly related to the quantum-chemically calculated values of electron affinities (A) and stabilization energies of radicals formed in the reduction of diazonium cations. Linear correlations between the frequencies (v) characterizing the set of stretching vibrations in the C—N⁺N fragment of XC₆H₄N⁺N cations and NN and C—N bond orders, charges on carbon atoms in the para positions of aromatic rings of C₆H₅X molecules, and mesomeric dipole moments (µ_m) of substituents X were found. Quantitative relationships relating µ_m and v to A were revealed. These relationships have clear physical meaning, are characterized by relatively large correlation coefficients, and possess predictive power for redox properties, electron affinity, and vibrational spectra of aryldiazonium cations and mesomeric dipole moments of atomic groups in organic molecules.Translated from Zhurnal Analiticheskoi Khimii, Vol. 60, No. 2, 2005, pp. 149–156. Original Russian Text Copyright © 2005 by Pankratov.     

Biosynthesis,purification and structure-property relationships of new cyanobacterial exopolysaccharides

Exopolysaccharides are considered as omnipresent and abundant bioproducts. However, the diversity of cyanobacteria offers a great opportunity for discovering new bioproducts as they are not properly explored. The current work targeted to characterize an indigenous cyanobacterial strain CCC-746 isolated from Bishnupur, India for production of exo-polysaccharides. The molecular and microscopic observation stated that the isolated cyanobacteria is Anabaena sp. The analysis of biomass composition showed carbohydrates, protein, lipid, ash and moisture content are 32.10%, 36.56%, 24.13%, 5.89% and 1.32% (w/w) respectively. The maximum production of EPS was 340.70 mg/L, when grown in 10 mM CaCl₂ supplemented BG11 medium. The capsular polysaccharide and released exo-polysaccharide were purified by gel filtration chromatography, and molecular weight was found as 12.52 and 9.2 kDa, respectively. The major component of both exo-polysaccharides was carbohydrate with glucose, xylose and glucuronic acid as major monosaccharides. Capsular polysaccharide and released exo-polysaccharide were composed of [→4)-Glcp-(1→] backbone. Both exo-polysaccharide were found negative in charge and showed remarkable antioxidant and scavenging activities. Capsular polysaccharide and released exo-polysaccharide solubilized in aqueous solution exhibited the behaviour of pseudo-plastic fluids.     

Systematic study of the structure-property relationship of a series of ferrocenyl nonlinear optical chromophores

A series of novel nonlinear optical (NLO) chromophores 1-4 incorporating the ferrocenyl (Fc) group as an electron donor and 2-dicyanomethylene-3-cyano-4-methyl-2,5-dihydrofuran (TCF) derivatives as electron acceptors are presented. The use of a constant Fc donor and varied acceptors and bridges makes it possible to systematically determine the contribution of the conjugated bridge and the acceptor strength to chromophore nonlinear optical activity. The X-ray crystal structures of all four chromophores allow for the systematic investigation of the structure-property relationship for this class of molecules. For example, the crystal structures reveal that both cyclopentadienyl groups in the ferrocenyl donor contribute to the electron donating ability. The first-order hyperpolarizabilities beta of these chromophores, measured by hyper-Rayleigh scattering (HRS) relative to p-nitroaniline are reported. These beta values are compared to those calculated by density functional theory (DFT). The excellent agreement between the theoretical and experimental beta values demonstrates that a linear relation exists between the hyperpolarizability and the bond length alternation. An electrooptic coefficient, r(33), of approximately 25 pm/V at 1300 nm, for compound 4, incorporated into a polymer matrix, is competitive with organic chromophores. Moreover, this r(33) is more than 30 times larger than the previously reported value for an organometallic chromophore in a poled polymer matrix. This work not only underscores the potential for Fc donor moieties, which have been underutilized, but also demonstrates that experimental characterization and theoretical simulations are now congruent, viable methods for assessing potential performance of NLO materials.     

Step-controlled synthesis of platinum(II) acetylide frameworks from conjugated polyaromatic modules

A simple synthetic route for the efficient preparation of mono- and dinuclear platinum(II) derivatives containing σ-bonded ethynyl aryl groups is described. A dinuclear complex pointing its two Pt-Cl dipoles in opposite directions is prepared either by complexation of a back-to-back terpyridine ligand with platinum salts or by cross-coupling [(4′-ethynylterpyridine)PtCl] with dibromodidodecylphenyl derivatives. FT-IR, UV-vis absorption and cyclic voltammetry are used as spectroscopic tools to characterize these new complexes.