(Super)gelators derived from push–pull chromophores: synthesis, gelling properties and second harmonic generation

Abstract

The present work takes advantage of the self-assembly process occurring along organogelation, to organize Second Harmonic Generation (SHG) active chromophores. To do so, three push-pull chromophores endowed with a dodecyl urea chain were synthesized and characterized. Their organogelating properties were studied in a wide range of solvents. Despite similar architectures, these derivatives exhibit very different gelling properties, from supergelation to the absence of gelling ability. The utilization of the Hansen solubility parameters allows for observing clear relationships between the gelled solvents and critical gelation concentrations. By evaporating the solvents from the organogels, xerogel materials were prepared and systematically studied by means of optical and electron microscopy as well as SHG microscopy. These studies demonstrate the critical role of the solvent over material structuring and allow generalizing the approach exploiting organogelation as a structuring tool to spontaneously organize push-pull chromophores into SHG-active materials.

Synthesis of Substituted Thiophenes through Dehydration and Heterocyclization of Alkynols

“…Based on the abovementioned control experiments and literature reports, a hypothesized mechanism for the sulfur cyclization reaction was developed (Scheme ). − To begin, initial activation of the hydroxyl group with HI produced from I 2 gave the propargyl carbocation intermediate A . Alternatively, the redox reaction of sulfur can yield protic acid.…”

“…Numerous efficient procedures for the preferential synthesis of 2,5-disubstituted thiophenes have been described previously, including the sulfur annulation of 1,3-butadiynes or internal alkynes with trisulfur radical anions (S 3 •– ) or CS 3 2– generated in situ from materials such as S 8 /NaO t Bu, Na 2 S, K 2 S, and CS 2 (Scheme a) . Similarly, elemental sulfur has been successfully used as an effective sulfur source in a pot procedure for the synthesis of substituted thiophenes . Moreover, the trisulfur radical anion (S 3 •– ) is effective in the synthesis of substituted thiophenes by the sulfur cyclization reaction of alkenynes or alkenes in an atom economy model (Scheme b) .…”

Dirhamnolipid ester – formation of reverse wormlike micelles in a binary (primerless) system

“…It should be emphasized that the formation of a gel structure was observed for concentrations as low as 0.5 wt %. Organogelators that are able to gel solvents at concentrations at <1% are classified as supergelators [29][30][31]. Furthermore, the results from the solubility tests where the ability of gelation decreases with an increasing alkyl chain length of the dirhamnolipid ester, could be confirmed.…”