A series of pyridyl-appended bis(urea) ligands form supramolecular gels in the presence of metal ions (metallogels), particularly copper(II) and silver(I). The gels have been characterised by rheometry and SEM, and the effect of the metal ions on gel strength and morphology examined. The metal-induced gelation is linked to the competition between urea–urea and urea–pyridyl hydrogen bonding interactions. Crystals grown from these gels reveal a wealth of structural information about these systems that can be related to gel structure using powder X-ray diffraction data of their xerogels.

This paper described the preparation of Langmuir-Blodgett (LB) films comprised of an oligomeric phenylene-ethynylene (OPE) derivative, 4-[4-(phenylethynyl)-phenylethynyl] benzoic acid (BPEBA). Analysis of the surface pressure and surface potential vs area per molecule isotherms reveal that good quality monolayer films can be formed at surface pressure of 15 nM/m. The monolayers were transferred onto solid substrates wth a Z-type depositions and a transfer ration of 1. Raman and surface-enhanced Raman spectroscopy (SERS) studies reveral that the films are physisorbed onto silver metal subtrates. The morphology of the deposited films wsa analyzed by means of atomic force microscopy (AFM), revealing the formation of homogeneous layers free of three-dimensional defects. The optical and emissive properties of the LB films were determined, with significant blue-shifted absorption spectra indicating the formation of two-dimensional H aggregates into the films. In addition, a significant Stokes shift in the excitation and emission spectra of the films is indicative of a distribution of molecular conformations around the long molecular axis in the solidlike monolayer environment. Scanning tunneling microscopy (STM) studies of single layer BPEBA LB films were performed. The tip-sample distance has been calibrated carefully to obtain I-V curves above the LB films I-V curves are unexpectedly symmetrical in spite of the asymmetric contacts of the molecule with the tip and the substrate. Single molecule conductance for BPEBA has also been determined and the similarity of these results to I-V data for BPEBA incorporated in LB films indicates that lateral (intermolecular conductance is negligible for electrical measurements using the STM configuration.

The Sonogashira cross-coupling of two equivalents of para-substituted ethynylbenzenes with 2,5-diiodothiophene provides a simple synthetic route for the preparation of 2,5-bis(para-R-phenylethynyl)thiophenes (R = H, Me, OMe, CF3, NMe2, NO2, CN and CO2Me) (1a–h). Likewise, 2,5-bis(pentafluorophenylethynyl)thiophene (2) was prepared by the coupling of 2,5-diiodothiophene with pentafluorophenylacetylene. All compounds were characterised by NMR, IR, Raman and mass spectroscopy, elemental analysis, and their absorption and emission spectra, quantum yields and lifetimes were also measured. The spectroscopic studies of 1a–h and 2 show that both electron donating and electron withdrawing para-subsituents on the phenyl rings shift the absorption and emission maxima to lower energies, but that acceptors are more efficient in this regard. The short singlet lifetimes and modest fluorescence quantum yields (ca. 0.2–0.3) observed are characteristic of rapid intersystem crossing. The single-crystal structures of 2,5-bis(phenylethynyl)thiophene, 2,5-bis(para-carbomethoxyphenylethynyl)thiophene, 2,5-bis(para-methylphenylethynyl)thiophene and 2,5-bis(pentafluorophenylethynyl)thiophene were determined by X-ray diffraction at 120 K. DFT calculations show that the all-planar form of the compounds is the lowest in energy, although rotation of the phenyl groups about the CC bond is facile and TD-DFT calculations suggest that, similar to 1,4-bis(phenylethynyl)benzene analogues, the absorption spectra in solution arise from a variety of rotational conformations. Frequency calculations confirm the assignments of the compounds’ IR and Raman spectra.

Ag(I) and Cu(II) complexes of a series of simple bis( urea) ligands form soft metallogels. X-ray crystallographic results suggests that the gels' structure is based on hydrogen bonding to counter anions and thus suggests a route to tunable gel rheological properties.

An extended dipyridyl ligand (L1) capable of hydrogen bonding with guest species via urea functionalities has been designed and synthesised. Assembly of a silver(I) coordination polymer of L1 is dependent on the nature of the hydrogen bond acceptor in a logical extension of the monopyridyl analogue.