Symmetrically bis-substituted indigo derivatives with long peripheral alkyl chains were synthesised by the reductive condensation of corresponding isatin derivatives. Their thermotropic mesomorphism was investigated with respect to different substitution patterns, which include the position and lateral modifications of the substituents. A systematic investigation of structure–property relationships revealed that only substitution at the 6 and 6′ positions affords the calamitic shape necessary to form smectic or nematic liquid crystalline phases. This finding is rationalised on the basis of a structural analysis of N,N′-diacetyl indigo and the consequences for 5,5′- and 6,6′-bis-substituted derivatives are discussed. Some of the liquid crystalline substances exhibit dichroism, which is especially pronounced in highly ordered phases. In addition, the 6,6′ substitution leads to significantly enhanced activity with respect to the photochemical trans–cis isomerization of N,N′-diacetylated indigo derivatives.

Carbohydrate- and oligoethylene oxide-based surfactants behave quite differently despite the fact that they are both classes of nonionic surfactants. Intensive studies of a mixture at fixed molar ratio (1:1) of two very common sugar- and oligoethylene oxide-based surfactants, namely n-dodecyl-β-d-maltoside (β-C12G2) and n-dodecyl hexaethylene oxide (C12E6), revealed that most properties of the mixture are similar to those of the oligoethylene oxide-based surfactant. In the present work, this mixture is compared to respective “hybrid surfactants”. Such hybrid surfactants are surfactants whose head group contains chemically linked carbohydrate and oligoethylene oxide units. In order to study the behaviour of this sort of compounds, we synthesised a new class of surfactants whose head group consists of one carbohydrate-like unit (myo-inositol) and three ethylene oxide units. New regiochemically defined ethoxylated inositol derivatives (referred to as C12I1E3 and C12E3I1 in the following) were synthesised and studied for their thermotropic and lyotropic liquid crystalline properties as well as for their surface activities. The results are compared with those of the reference systems β-C12G2 and C12E6, and their 1:1 mixture, respectively, and are discussed in terms of structure–property relations.Graphical abstractHighlights► Synthesis of two nonionic ethoxylated inositol-based surfactants C12E3I1 and C12I1E3. ► Properties are driven by the way the head group is attached to the alkyl chain. ► Recipe to tailor-make effective surfactants with hybrid head groups.

Carbohydrates are versatile materials of natural origin and thus they are interesting hydrophilic head groups for surfactants. Especially myo-inositol derivatives have advantages over pyranosidic or furanosidic sugar derivatives, namely a higher thermal and chemical stability. The main disadvantage turned out to be the poor water solubility of myo-inositol surfactants, which, however, can be overcome by introducing an oligoethylene oxide group between the inositol head group and the apolar chain. Our goal was to combine the favourable properties of surfactants based on myo-inositol with those of fluorinated surfactants, which are becoming increasingly important as CO2 solvation mediators or stabilizers for reverse water-in-fluorocarbon microemulsions. Thus we synthesized a new surfactant which combines the three units of interest, namely an inositol head group, an oligoethylene oxide linker to provide sufficient solubility and a fluorinated chain. We studied the thermotropic and lyotropic liquid crystalline behaviour as well as the surface tension and compared these results with those of a fully protonated surfactant which has a similar structure.Graphical abstractMolecular structure, lyotropic lamellar phase and surface tension of the partly fluorinated, new inositol-based surfactant C6FC3HE2I1.Highlights► Synthesis of fluorinated inositol-based surfactant C6FC3HE2I1. ► Properties are dominated by fluorinated chain. ► Recipe to tailor-make fluorinated surfactants with hybrid head groups.

The synthesis of a homologous series of 5-(4-alkylphenyl)isatin derivatives, as well as the crystal structure and DFT studies of the respective hexyl derivative are presented, constituting the first examples of a new family of supramolecular bilayer forming isatin derivatives, which reveal a new type of molecular strand—a molecular arrangement also supported by quantum chemical calculations.

Carbohydrates are interesting starting materials for scientific and industrial syntheses as they allow a versatile chemistry. Moreover, they are of natural origin and environmentally benign. During the past few years, inositol, a rather “exotic” carbohydrate, and its derivatives have gained increasing attention. Here, we describe the syntheses of new regiochemically defined inositol monoethers and monoesters as well as regioisomeric inositol ester mixtures and investigate their amphitropic liquid crystallinity. Furthermore, first results on their surface activity in aqueous solutions are given and compared with classical sugar surfactants.

Alkyldimethyl (CnDMPO) with chain lengths of n = 8 (octyl), 10 (decyl), 12 (dodecyl), and 14 (tetradecyl) as well as alkyldiethyl (CnDEPO) phosphine oxides with chain lengths of n = 10, 12, and 14 were synthesized and purified to study how the adsorption properties and the location of the miscibility gap of these surfactants depend on the size of the head group and on the length of the alkyl chain. After surfactant purification, the surface tension isotherms were determined from which the cmc, the minimum surface tension σcmc, the maximum surface concentration Γmax, and the minimum surface area Amin were obtained. As expected, for one homologous series, a decrease in the cmc and an increase in Γmax was observed with increasing alkyl chain length. For two surfactants of the same alkyl chain length, the cmc values of the CnDEPO surfactants are approximately two times lower than those of the CnDMPO surfactants. However, the Γmax values of CnDEPO are lower than those of CnDMPO as two ethyl chains are sterically more demanding than two methyl chains. In addition to the adsorption properties, the location of the miscibility gap as a function of the alkyl chain length and the head group size was studied. Its location depends on the total number of carbon atoms and not primarily on the length of the main alkyl chain. This observation reflects the decreasing water solubility which can be tuned by increasing the length of either the main alkyl chain or of the shorter head group chains.

The interest in designing highly specialised synthetic surfactants incorporating natural structural motifs has increased remarkably during the last few years. The variety of naturally occurring structures used as parts of such “designer surfactants” ranges from simple amino acids and short peptides over carbohydrates to steroids. Surely, one of the most prominent examples in this respect and probably the breakthrough for tailor-made surfactants in highly specialised applications was the use of a surfactant for the first successful crystallisation of a membrane protein, a great feat for which the Nobel Prize in Chemistry was awarded in the year 1988. Moreover, the ability of certain specialised surfactants to accelerate the transport of genetic material or drugs through biological membranes is widely taken advantage of in biotechnology and pharmacy. The most important applications for surfactants, however, are related to their self-organisation in solution. Self-organisation leads to the formation of micelles, liposomes, lyotropic liquid crystalline phases, and microemulsions. These self-organised structures are used for solubilisation, transport, and separation processes, as templates for nanoparticles, as models for biomembranes, and as reaction media, to mention just a few. In all these applications surfactants designed on the basis of natural compounds are either desirable or even indispensable. An overview of some of our recent synthetic work in the field of “new speciality surfactants with natural structural motifs”, partly taking advantage of the “chiral pool”, will be given and future perspectives will be discussed.