Effects of constitutional isomerism on molecular ordering and thermal shifts.

We introduce naphthol-cholesteryl dimers showing that constitutional isomerism in a rigid core dictates mesophase structure and thermal stability. Planar naphthalene-diol cores linked to a chiral cholesteryl segment via flexible spacers permit subtle substitution changes that switch packing from V-shaped branches to linear rods, sharply altering the mesophase type and transition temperatures. Linear para-isomers promote tight π-π stacking, elevating average clearing temperatures (TC) above 177 °C and broadening the nematic phase range. In contrast, V-shaped variants lower TC to an average of 135 °C. XRD shows intercalated SmA layers, and UV-vis reveals concentration-dependent H-aggregation in the 2,6-series. Both dimers exhibit monomer/excimer fluorescence; 2,6-NCh-Dn shows enhanced solid-state emission and larger Stokes shifts-a difference that highlights aromatic geometry as a key template when designing mesogens.