The effect of spacer length between the polar group and the aromatic core on the self-assembly and emission behaviours of amphiphilic mesogens

Understanding how structure governs self‑assembly and photophysical properties is key to designing functional soft materials. Amphiphilic mesogens are an ideal molecular platform for structure–property investigations, owing to their microsegregation‑driven assembly, rich intermolecular interactions, tunable mesophases and attractive optoelectronic properties. Herein, we designed three series of cyanostilbene-based amphiphilic mesogens to systematically investigate how spacer lengths modulated the mesophase and photophysical properties. All amphiphilic mesogens bearing one cyanostilbene core, three terminal non‑polar alkyl chains with different lengths and one terminal polar diol unit with variable spacer lengths were synthesised via a multi-step route involving etherification, Suzuki coupling, dihydroxylation and Knoevenagel condensation. Their mesomorphic behaviour was systematically investigated using POM, DSC and SAXS. For homologues with the shortest spacer, a temperature-dependent and chain-length-dependent mesophase transition from a hexagonal to a cubic mesophase was achieved. In contrast, homologues with longer spacers exclusively stabilised the hexagonal mesophase. Molecular dynamics simulations corroborated the proposed packing models. Furthermore, all derivatives exhibited AIE behaviour in tetrahydrofuran–water mixtures due to distorted molecular conformation, as proved by DFT calculations, and the spacer length had little effect on the AIE behaviour. This work provides fundamental insights into the effect of molecular engineering on self‑assembly and photophysical characteristics, offering guidelines for rational soft‑materials design.