Helical Conformations of Poly(3,5-disubstituted phenylacetylene)s Tuned by Pendant Structure and Solvent

A series of novel <i>cis</i> poly­(phenylacetylene)­s (PPAs) substituted at the <i>meta</i>-position(s) by both achiral alkoxycarbonyl and chiral alkylamide groups, i.e., <b>rP-I</b>, <b>sP-I</b> to <b>sP-V</b>, or by just a chiral alkylamide group, i.e., <b>rP-VI</b>, were synthesized under catalysis of [Rh­(nbd)­Cl]₂. The dependence of the elongation, screw sense, and stimuli response of helical polyene backbone on the structure and number of substituent was systematically investigated in both solution and solid states. Stretched <i>cis–transoid</i> helices with opposite signs coexisted in the DMF solution of either <b>sP-I</b> or <b>rP-I</b>, but a single handed, contracted <i>cis–cisoid</i> one formed in the mixture of DMF/THF (10/90, v/v). Increasing the substituent size made the polymers <b>sP-III</b>, <b>sP-IV</b>, and <b>sP-V</b> to take only single handed stretched <i>cis–transoid</i> helical conformations regardless of the solvent polarity. The <i>N</i>-methylation of the amide group in <b>sP-II</b> caused a similar effect. With the removal of achiral methoxycarbonyl substituent, <b>rP-VI</b> took just a stretched <i>cis–transoid</i> helical conformation in polar DMF, whereas it existed as a mixture in equilibrium of stretched <i>cis–transoid</i> and contracted <i>cis–cisoid</i> helices with identical screw sense in less polar solvents such as dioxane, THF, and chloroform. The twisting directions of substituent array and polyene backbone were found to be coincident in a dynamic, contracted helix, but the opposite in a less dynamic, stretched helix. These results suggested that the 3,5-disubstitution, strong intramolecular hydrogen bonding, and small substituent favored the formation of contracted <i>cis</i>–<i>cisoid</i> helices for PPAs

Assembly of peptide–thiophene conjugates: the influence of peptide content and location

<div><p>Biomolecule-directed self-assembly of π-conjugated oligomers has attracted great attention in the past decade. In this contribution, two conjugates composed of quaterthiophene and tetrapeptide (Gly-Val-Gly-Val) were synthesised, namely peptide–thiophene–peptide (PTP) and thiophene–peptide–thiophene (TPT), to investigate the influence of peptide content ratio and its location in the molecular structures on the nanostructures and properties of the assemblies. Both conjugates formed organogels consisting of left-handed twisted nanostructures; however, anti-parallel β-sheets were observed in PTP while parallel β-sheets were obtained for TPT, although in both cases oligothiophenes adopted an H-like stacking mode. Obvious solvent-induced supramolecular chirality inversion from the oligothiophene segment was observed for PTP while such phenomenon was not clear for TPT. PTP and TPT gels also showed different stabilities towards temperature increase, as evidenced by variable-temperature circular dichroism study. From the data, it is suggested that the rational design of the location and ratio of peptide plays a key role in constructing materials with determined properties based on peptide–thiophene conjugates.</p></div

2,5,8,11-Tetraalkenyl Perylene Bisimides: Direct Regioselective Synthesis and Enhanced π–π Stacking Interaction

A series of 2,5,8,11-tetraalkenyl perylene bisimide (PBI) derivatives were synthesized through Ru­(II)- or Rh­(III)-catalyzed regio- and steroselective oxidative C–H olefination in one step. The optical electronic and self-assembly of the 2,5,8,11-substituted PBIs were investigated, which showed great potential in optoelectronic applications

Induction of Chirality in an Achiral Monolayer at the Liquid/Solid Interface by a Supramolecular Chiral Auxiliary

An achiral oligo­(<i>p</i>-phenylene vinylene) derivative with a ureido-triazine hydrogen bonding unit self-assembles into rows of hydrogen bonded dimers at the liquid/solid interface. Scanning tunneling microscopy reveals the formation of chiral domains, but overall, the surface remains racemic. Addition of a chiral auxiliary which is able to interact with the dimers through hydrogen bonding, showed that global organizational chirality could be achieved since a majority of the domains show the same handedness. After removing the chiral auxiliary with a volatile solvent, the global organizational chirality could be trapped, revealing a memory effect. With this straightforward supramolecular approach, we were able to create a chiral surface with preferred handedness composed of achiral molecules at the air/solid interface