Heteroaromatic Spacer Research Articles

Hantzsch one-pot multicomponent synthesis of a novel series of bis(9,10-diarylhexahydroacridine-1,8-diones)

Efficient procedures have been developed for the synthesis of novel series of bis(9,10-diaryl-hexahydroacridine-1,8-diones) in which the two acridine moieties were linked to aliphatic, aromatic, or heteroaromatic spacers via ether or ester linkages. The target products were obtained in good to excellent yields via a multi-component reaction of the appropriate aromatic amine, 5,5-dimethyl-1,3-cyclohexanedione, and the corresponding bis-aldehydes. The reactions were also proceeded to give the target products in good yields via a multi-component reaction of the appropriate cyclic enamines, and the corresponding bis-aldehydes under similar conditions. Bis-alkylation of the appropriate hexahydroacridine-1,8-dione with the corresponding dihalo compound in a basic medium was also proved to be an effective strategy for the synthesis of the target products. The multi-component reaction of the aromatic amine, bis-aldehydes, and barbituric acid or 1,3-dimethylbarbituric acid, instead of 5,5-dimethyl-1,3-cyclohexanedione, afforded the corresponding Knoevenagel condensation adducts in good yield and unfortunately, the expected bis-tetrahydropyrimido[4,5-b]quinolines could not be isolated.

A Computational Study of Expanded Heterocyclic Nucleosides in DNA

The first molecular dynamics study of a series of heterospacer-expanded tricyclic bases in DNA using modified force field parameters in AMBER is detailed. The expanded purine nucleoside monomers have been designed to probe the effects of a heteroaromatic spacer ring on the structure, function, and dynamics of the DNA helix. The heterobase scaffold has been expanded with a furan, pyrrole, or thiophene spacer ring. This structural modification increases the polarizability of the bases and provides an additional hydrogen bond donor with the amine hydrogen of the pyrrole ring or hydrogen bond acceptor with the furan or thiophene ring free electron pairs. The polarizability of the expanded bases were determined by AM1 calculations and the results of the MD simulations of 20-mers predict that the modified curvature of the expanded base leads to a much larger major groove, while the effect on the minor groove is negligible. Overall, the structure resembles A-DNA. MD simulations of 10-mers suggest that the balance between base pairing vs. base stacking and intercalation can be shifted towards the latter due to the increased surface area and polarizability of the expanded bases.

Di-tungsten Bis-carbene Complexes Linked by Condensed Heteroaromatic Spacers

The 2,7-dilithiated substrates of 3,6-dimethylthieno[3,2-b]thiophene, N,N′-dimethylpyrrolo[3,2- b]pyrrole and N-methylthieno[3,2-b]pyrrole were reacted with W(CO)6 to give, after subsequent alkylation with Et3OBF4, the ditungsten biscarbene complexes [(CO)5W{C(OEt)XXC(OEt)} W(CO)5] (XX = condensed heteroaromatic spacers). Sites of attack during the dilithiation of the condensed rings were studied and compared, and the yields of the desired ditungsten biscarbene complexes optimized by changing the reaction conditions according to the role of the heteroatoms in the rings. The crystallographic data of the three ditungsten biscarbene complexes are reported and their structural features compared. The methyl substituents on the condensed heteroaromatic rings play an important role in determining the molecular configurations.

Effects of 5-Membered Heteroaromatic Spacers on Structures of Porphyrin Films and Photovoltaic Properties of Porphyrin-Sensitized TiO2 Cells

Novel 5-(5-carboxy-2-thienyl)-10,15,20-tris(2,4,6-trimethylphenyl)-porphyrinatozinc(II) (Zn5S), 5-(5-carboxy-2-furyl)-10,15,20-tris(2,4,6-trimethylphenyl)porphyrinatozinc(II) (Zn5O), and 5-(4-carboxy-2-thienyl)-10,15,20-tris(2,4,6-trimethylphenyl)porphyrinatozinc(II) (Zn4S) were synthesized to evaluate the spacer effects on the structures of the porphyrin films and the photovoltaic properties of the porphyrin-sensitized TiO2 solar cells. Each of the porphyrins showed different adsorption behavior and saturated coverage on the TiO2 surface and photovoltaic properties depending on the identity of heteroatoms in the bridge and the position of carboxylic acid. Specifically, Zn5S-sensitized TiO2 cell displayed larger, maximum incident photon-to-current efficiency of 65% and maximum power conversion efficiency of 3.1% than Zn5O-sensitized TiO2 cell by ∼20% and ∼40%, respectively. We interpret that these results are stemmed from ancillary electron-transfer pathway through specific interaction between a sulfur at...

Synthesis and Z-scan measurements of third-order optical nonlinearity in push–pull molecules with dihydroxylethyl amino donor and nitro acceptor

Novel azo diol chromophores were synthesized through multi-step azo-coupling reaction and characterized by NMR, IR, and UV. The third-order NLO properties of the chromophores were investigated. The measurements of second hyperpolarizabilities were performed using single-beam Z-scan technique with picosecond laser pulses at 1064 nm in DMF solutions. Our results indicate that larger second hyperpolarizabilities γ can be readily obtained in such chromophores because of increase of molecular conjugation length and donor–acceptor conjugation path. Further enhancement of γ has been achieved via replacement of phenyl rings in the conjugated backbone by heteroaromatic spacers such as benzothiazole and pyrimidine rings. Therefore, it is very probable that the increase in the obtained γ values considerably arises from the conjugation path of the delocalized electrons for large third-order nonlinear optical effects.

Optical and Electronic Properties of Metal-containing Poly-ynes and their Organic Precursors

ABSTRACTA series of platinum(II) di-yne complexes with the general formula [PhPt(PR3)2-C≡C-X-C≡C-Pt(PR3)2Ph] where R = Et, nBu and X = a range of extended hetero-aromatic spacer groups, have been prepared by the coupling reaction between two molar equivalents of [PhPt(PR3)2Cl] and one molar equivalent of the terminal dialkyne, HC≡C-X-C≡CH, in the presence of CuI catalyst. The complexes have been characterised by IR, NMR and optical spectroscopy. These materials, which are precursors to related platinum(II) poly-yne polymers, have been specifically designed to be incorporated into metal-molecule-metal junctions in nanoelectronic devices.

Modulation ofπ-Electron Conjugation in Oligo(triacetylene) Chromophores by Incorporation of a Central Spacer

A comprehensive series of trimeric hybrid oligomers 4 – 14 (Fig. 2) was prepared by insertion of different hetero-spacers between two (E)-hex-3-ene-1,5-diyne (=(E)-1,2-diethynylethene, DEE) moieties, and the optical and electrochemical properties of the resulting π-conjugated materials compared to those of the DEE dimer 2 and trimer 3, which formally contains a DEE moiety as homo-spacer. The hetero-spacers varied from benzenoid (phenylene, naphthalene, biphenylene, anthracene), to π-electron-deficient (pyrazine, pyridine) and π-electron-rich (thiophene, furan) aromatic rings, and to an organometallic trans-Pt(PEt3)2 fragment. The hybrid oligomers were synthesized following a general strategy which relied on the Sonogashira cross-coupling between mono-deprotected DEE 15 and the appropriately bis-functionalized spacer (Scheme and Table 1). UV/VIS Studies revealed that the majority of the hetero-spacers were less effective than the homo-spacer DEE in facilitating π-electron delocalization along the linearly conjugated oligomeric backbone (Table 2 and Fig. 3). With increasing degree of benzenoid aromaticity in the hetero-spacer, the electronic communication between the terminal DEE moieties in the hybrid oligomers was reduced. As a remarkable exception, a large bathochromic shift of the longest-wavelength absorption maximum, which is indicative of enhanced π-electron delocalization, was obtained upon introducing an anthracene-9,10-diyl moiety as hetero-spacer into oligomer 7 (Figs. 3 and 6). Electrochemical investigations by cyclic and steady-state voltammetry confirmed the limited extent of π-electron delocalization in the majority of the hybrid oligomers (Table 3). The fluorescence properties of many of the DEE hybrid materials were dramatically enhanced upon incorporation of the hetero-spacers (Table 2). The heterocyclic derivatives 10 – 12, containing pyridine, pyrazine, or thiophene spacers, respectively, displayed a strong fluorescence emission, which is present to a significant extent neither in DEE homo-oligomers nor in the individual heteroaromatic spacer components, demonstrating the value of combining different repeat units to modulate oligomeric and polymeric properties. The pyridine derivative 10 provided an interesting example of a molecular system, in which both the electronic absorption (Fig. 4) and emission characteristics (Table 2) can be reversibly switched as a function of pH (Fig. 5).

Effect of heteroaromatic spacers on the structure and electrical properties of cation radical salts of tetrathiafulvalene analogs

The X-ray crystal structure of single crystals of electrocrystallized cation radical salts of 2,5-bis(1,3-dithiol-2-ylidenemethyl)-thiophene and -furan1and2 have been analysed. Both cation radicals adopt asyn conformation stabilized by strong intramolecular interactions. Bond length analysis reveals that the positive charge is delocalized over the whole molecule with enhanced delocalization for 2+ containing the less aromatic furan cycle. Whereas 2+ cation radicals are uniformly stacked along the c axis with interstack interactions, 1+ forms weakly interacting dimers stacked along the b axis. In agreement with an enhanced charge delocalization and increased dimensionality, 2BF4 shows a conductivity ca. three orders of magnitude higher than 1ClO4 .

The Important Role of Heteroaromatics in the Design of Efficient Second-Order Nonlinear Optical Molecules: Theoretical Investigation on Push−Pull Heteroaromatic Stilbenes

First hyperpolarizabilities of a large number of push−pull substituted conjugated systems with heteroaromatic spacers have been calculated. The static, nonresonant components were computed at the ab initio level (4-31G basis) using the coupled perturbed Hartree−Fock approach and at the AM1 level employing the finite field method. Sum-over-states procedure has also been used with the AM1/CI method to compute β0 and β at an excitation energy of 1.17 eV. The computed β values at the various levels are reasonably similar and exhibit the same trends. The largest values are obtained with a donor on pyrrole and an acceptor on thiophene or thiazole. The variations do not always inversely follow the order of delocalization energies of the heterocyclic rings. The trends in the dipole moment changes and transition energies between the ground and first excited charge-transfer state primarily determine the variations in the computed β values.

Studies on Ketoses, 7 – 5‐(α‐D‐Glucosyloxymethyl)furfural: Preparation from Isomaltulose and Exploration of Its Ensuing Chemistry

AbstractAn effective, practical, large‐scale adaptable procedure has been developed to selectively dehydrate the fructose portion of isomaltulose [glucosyl‐α(1→6)‐fructose] (6): heating in DMSO in the presence of a strongly acidic ion‐exchange resin generates α‐D‐glucosyloxymethylfurfural (“α‐GMF”, 3), isolable in yields up to 70%. A variety of ensuing reactions have been exploited concerning the generation of products with industrial application profiles such as aldol‐type additions to the dicyanovinyl (16), nitrovinyl (20), and benzoylvinyl (21) derivatives, or to the polymerizable unsubstituted vinyl compound (25) and the GMF‐acrylic acid (22). Oxidation to GMF‐carboxylic acid (11) and reductive amination to GMF‐amine 8 can be carried out without affecting the hydroxyl groups in the glucosyl portion; esterification of 11 with long‐chain alcohols and N‐acylation of 8 with fatty acid chlorides provide novel surfactants in which hydrophilic and hydrophobic parts of the molecule are separated by a heteroaromatic spacer.

Diporphyrinyl derivatives of 1,10‐phenanthroline and 2,2′‐bipyridyl

AbstractThe title derivatives were synthesized containing two meso‐tri‐p‐tolylpheneleneporphyrin units attached via amide bridges to 4,7‐ and 4,4′ positions of the respective heteroaromatic spacers.