Novel selenoesters fluorescent liquid crystalline exhibiting a rich phase polymorphism

A simple and efficient procedure for the synthesis of a new class of selenoesters 4a and 4b was developed. Polarized-light optical microscopy (POM), differential scanning calorimetry (DSC), and X-ray diffraction showed that the selenoester 4a with a shorter alkyl chain displayed a wide nematic range (Delta T = 110.7 degrees C), while 4b with a longer alkyl chain possesses a rich phase polymorphism: Cr -> SmI -> SmC -> N -> I mesophase sequence during heating cycle and I -> N -> SmC -> SmI -> SmX -> Cr transition on cooling. For 4b, a large temperature range (135.7 degrees C) from crystal to isotropic phase can be observed. In addition, UV-Vis, steady-state fluorescence emission and excitation spectra in solution were also applied in order to characterize their photophysical behaviour. Compounds 4a and 4b are fluorescent in the blue region and present a Stokes shift at around 80 nm and 39 nm in dichloromethane and dioxane, respectively.