The material commonly known as DIO was reported virtually the same time as the RM-type materials; the combination of a 1,3-dioxane ring, carboxylate ester, and aromatic fluorination pattern gives a large longitudinal electric dipole moment. Although less well explored than the RMtype materials, a number of structural variations on this core structure are known. Increasing the molecular dipole moment by replacing the monofluorophenyl with 2,6-difluorophenyl gives a large (>50 °C) increase in the onset temperature of the NF phase; conversely, replacement with a 2methoxyphenyl unit reduces TN F -N slightly, while replacement with an unsubstituted benzene ring eliminates the NF phase entirely. Replacement of the ester unit of DIO with the germinal difluoromethyl unit (and also shortening of the terminal chain from propyl to methyl) eliminates the NF phase, irrespective of the molecular structure at rings #3 and #4. In terms of their ability to generate the NF phase this suggests that the CF2O linking unit is inferior to an ester, however, as will be shown later, this unit has been utilised in ferroelectric nematic materials. 28