MP SmAd-N N-Iso The layer spacing of the SmAd phase of 11 was measured by SAXS (Figure SI-1)and was found to be temperature independent at 34.3 Å, corresponding to a d/l ratio of 1.60 using the molecular length of 21.4 Å (from geometry optimised at the B3LYP/6-31G(d) level). This result, which is the same as for compound 9, supports the hypothesis that the enhancements to layer spacing and transition temperatures result from segregation of the bulky end group via reducing the interpenetration of alkyl chains between adjacent smectic layers. Although the end-to-end length (and therefore the aspect ratio) of the antiparallel paired species remains the same with a bulky end group present the effective aspect ratio (i.e. interlayer biphenylbiphenyl distance) is increased due to this reduced interpenetration, leading to higher transition temperatures. Previously we have obtained values of the semi-empirical Kirkwood factor (g, effectively a measure of the degree of pairing in an anisotropic liquid) from measurement of the dielectric anisotropy coupled with calculated dipole moments and polarisabilities. While this information would clearly be desirable for the present materials, the short nematic range of 9 and 11 leads to an unsaturated value of Δε and therefore of the Kirkwood factor.