Dimerization of nematic liquid crystals can enhance the birefringence (Dn) without red-shifting the absorption band edge. At a nematic temperature of 10 degrees C higher than the crystal melting point, Dn of the bistolane-based dimer is 0.51, which is 1.2 times larger than that of the corresponding monomer (0.42), but the dimer has the same absorption edge at 375 nm as the monomer. This larger Delta n is explained by the larger polarizability anisotropy in the spacer stretching along the nematic director.