Synthesis, liquid crystalline properties and photo switching properties of coumarin-azo bearing aliphatic chains: Application in optical storage devices

A series of novel azo-coumarin derivatives with different aliphatic chain length (3a-e) have been synthesized and characterized for liquid crystal properties and their photoswitching behavior. The incorporation of coumarin along with azobenzene was prepared via esterification reaction and differ in the length of alkyl group, CnH2n+1, where n = 6, 8,10,12 and 14. Azo-coumarin bearing C-14 alkyl chain shows Smectic-A phase while azo-coumarin bearing rest of long alkyl chain exhibited Nematic phase. The incorporation of natural product moieties into azobenzene network has increased electron delocalisation and liquid crystal properties. The photoswitching properties of said molecules were tested and the coumarin-azo compounds 3a-e took similar to 46 s to reach photostationary state during UV illumination and exhibited long thermal back relaxation time (similar to 16 h) in solutions. Device is also fabricated to see the performance of the device with respect to the alkyl chain length. Presented studies show the importance of azo-coumarin derivatives with different chain length for the application of optical storage devices. (C) 2019 Elsevier B.V. All rights reserved.