Smectic phase formation in unsymmetric dimeric polycatenar mesogens

We report the synthesis and mesomorphic characterisation of two unsymmetric dimeric polycatenar mesogens (A1 and A6) incorporating an odd-membered flexible spacer and a 3,4,5-tris(hexyloxy) polycatenar terminus. The dimers were comprehensively characterised for their mesophase behaviour using differential scanning calorimetry (DSC), polarised optical microscopy (POM), and temperature-dependent small- and wide-angle X-ray diffraction (XRD). Despite combining bent molecular geometry with a multi-chain architecture, both compounds form only enantiotropic smectic phases. Compound A1 displays a single SmA phase (mesophase range 9 K), while A6 shows a SmA phase followed by a second, unidentified lamellar smectic phase of higher positional order (combined smectic range 42 K). X-ray diffraction reveals an intercalated bilayer-like SmA packing for A1 and an essentially monolayer lamellar arrangement for A6. The observation of orthogonal SmA phases in these unsymmetric polycatenar mesogens is discussed in the context of space-filling constraints and cross-sectional mismatch between the rigid core and the terminal chain volume.