Annette Oehlhof

Supramolecular order of stilbenoid dendrons: importance of weak interactions

Stilbenoid dendrons with various donor and acceptor groups on the focal unit were synthesised by a Wittig–Horner reaction, starting from an aldehyde functionalised dendron and various substituted phosphonic acid esters. The target molecules are composed of meta-branched arms, two of them with extended conjugation (distyrylbenzene) and three flexible dodecyloxy chains; the focal group consists of a donor or acceptor substituted styryl unit. The cross-conjugation of the arms prevents the strong electronic influence of substituents on the two extended oligophenylenevinylene chromophores. However, intermolecular interactions mediated by the focal unit allow control of the supramolecular stacking into liquid crystal phases. Simple weak acceptors stabilise the formation of columnar phases, whereas the additional propensity to build hydrogen bonds leads to a cubic mesophase. All acceptor substituted materials freeze at low temperature into a glassy state. Soft crystals are then formed upon heating the glassy material. Stilbenoid dendrons are photosensitive and degradation of the supramolecular order proceeds even in the glassy liquid crystal state.

Equilibrium between Hydroxycycloalkanones and Oxabicycloalkanols

Hydroxycycloalkanones 1 of medium ring size (8 -10) exist in a transannular tautomeric equilibrium with the corresponding oxabicycloalkan-1-ols 2, which represent hemiacetals. Normally, the bicyclic structures 2 predominate in solution although their portion decreases with increasing solvent polarity. A correlation of the Gibbs reaction enthalpies ΔG (1→2) with the solvent parameters ET (30) is presented. Graphical Abstract Equilibrium between Hydroxycycloalkanones and Oxabicycloalkanols

Comparison of Alkoxy-substituted 4,4 -Distyrylbiphenyls and the Corresponding 4,4 -Distyrylbenzenes

Abstract Configurationally highly pure (E,E)-4,4´-bis(styryl)biphenyls 2a - e were obtained by Siegrist reactions of 4,4´-dimethylbiphenyl 3 and alkoxy-substituted benzaldimines (4a - e). DSC measurements have indicated different crystalline modifications of these conjugated compounds. The stilbenoid chromophores of 2a - e are compared to the stilbenoid chromophores in the OPV series, which have a similar length of conjugation. The intense fluorescence and the high transparency in the visible region are promising properties for an application of the donor-substituted compounds 2a - e in twophoton absorption (TPA) techniques.