•New LC dimers with azo or azomethine naphthalene synthesized and characetrized.•Even-spacer dimers are nematogenic, whereas odd-spacer dimers are non-mesogenic.•Structure-property relationship discussed for synthesized dimers of both series.•NpAmDn series exhibits wider mesophase ranges than NPAzDn.•DFT analyzed, structure optimized, and vibrational frequencies studied.•Azo dimers undergo photoisomerization when exposed to 360 nm light. The reactions of different α,ω-dibromo alkanes with (E)-4-(naphthalen-2-yldiazenyl)phenol and (E)-4-(naphthalen-2-ylimino)methyl)phenol, respectively, led to the synthesis of two new homologous series of liquid crystalline symmetrical dimers with azobenzene or azomethine central linkage and containing the naphthalene moiety as a rigid core. Spectroscopic techniques like FT-IR, 1H NMR, 13C NMR and elemental analysis confirmed their structure. These dimers exhibited mesomorphic phases, studied through POM and DSC. Their photophysical behaviour was explored using UV–visible spectroscopy. Remarkably, dimers with even spacer units (n = 2, 4, 6, 8, 10, 12) displayed excellent liquid crystalline properties as nematic phases, with extended mesophase lengths and thermal stability for both series. The study revealed the vital role of spacer length in determining liquid crystalline behaviour. The computational studies employed the B3LYP method and electron density method for optimization. Display omitted