Ultraviolet Stability Of Liquid Crystals Containing Cyano And Isothiocyanato Terminal Groups

The ultraviolet (UV) stabilities of liquid crystal compounds containing cyano (CN) and isothiocyanato (NCS) terminal groups are compared. UV exposure is found to degrade the clearing temperature, birefringence, dielectric constants and visco-elastic coefficient of the liquid crystal compounds. The measured data show that the NCS molecular structure exhibits a better UV stability than do the corresponding CN structures. Lewis resonance structures are used to explain this phenomenon