Liquid crystalline cyclic tetramethyltetrasiloxanes containing coumarin moieties

A series of new cyclic tetramethyltetrasiloxanes with coumarin units were synthesized. By a comparative study with their related vinyl terminated precursors, the liquid crystalline properties of the cyclic tetramethyltetrasiloxanes were investigated. The results show that the thermal properties of the cyclic tetramethyltetrasiloxanes are stabilised through their increasing clearing temperatures and broadening mesophases. The thermal properties of the cyclic tetramethyltetrasiloxanes show that introduction of a tail group at the 3 position of the coumarin unit increases the thermal stability of the liquid crystalline order. Increasing the length of the tail group causes the clearing temperatures of the cyclic tetramethyltetrasiloxanes to decrease. The photochemical behavior of spin-coated films of the cyclic tetramethyltetrasiloxanes indicates the photo-crosslinking of the coumarin units in the thin films.