Organic dielectric materials that can respond to electric fields have drawn much attention because of their potential applications to memory and sensing devices. One of the essential requirements for organic dielectric materials is the ability of changing the overall dipole moment in response to external electric fields. In this context, sumanene derivatives featuring a bowl-shaped skeleton are attractive, because they undergo a bowl-to-bowl inversion, which is accompanied by the inversion of the molecular dipole. As the bowl-to-bowl inversion would be facilitated in soft mesophases, liquid-crystalline (LC) sumanenes, for example, are expected to provide an interesting building block for the design of organic dielectric materials. While many examples of crystalline sumanenes have so far been reported, there is no sumanene derivative that can exhibit an LC mesophase. We recently found that sumanene, when carrying six alkyl side chains, successfully shows an LC mesophase over a wide temperature range. Herein, we report the synthesis, assembly structure, and dielectric properties of the new hexa-substituted sumanenes.