to about 10 (preferably, 3 to about 7) for each (Cs H2s O), t is an integer of 1 to about 6 (preferably, 1 to about 3; more preferably, 1 to 2), and r' is an integer of 1 to about 10 (preferably, 1 to about 5; more preferably, 1); with the proviso that the compounds do not exhibit at least one tilted smectic mesophase.