The role of flexible amide spacers in the self-assembly of star-shaped triphenylbenzenes with photoactive triphenylamine units: stimuli-responsive liquid crystals and gels†

This work reports on the decisive influence of the length of flexible amide spacers for obtaining soft materials out of star-shaped molecules. Either liquid crystal behaviour or gel behaviour was found for 1,3,5-triphenylbenzene connected to three triphenylamine units through flexible amide spacers with different numbers of carbon atoms. The spacer of two carbon atoms induces liquid crystal behaviour but not gel formation. Conversely, an analogous compound with a three carbon atom spacer is not liquid crystalline and forms gels in different solvents. The obtained liquid crystal phase shows a hexagonal columnar organization responsive to electric fields, allowing the material to be aligned homeotropically in ITO cells, that is, with the columns perpendicular to the electrodes and parallel to the applied electric field. Taking advantage of the photoactivity of triarylamine units bearing amide groups, the response under light irradiation in the gel state was explored.