Effective tuning of optical storage devices using photosensitive bent-core liquid crystals

Abstract

Abstract We discuss three series of substituted resorcinol based bent-core liquid crystals with azobenzene wings, substituents consisting of methyl (-CH3) and halogens ( F, Cl, Br) on the resorcinol core connected to azobenzene wings with variable alkoxy chains. The effect of electron-donating (-CH3) and electron-withdrawing (halogens) group on the photoisomerization and thermal back relaxation studied using UV–Vis spectroscopy. 4-methyl resorcinol bent-core (BC) exhibits the longest thermal back relaxation of about 16.33 h; whereas, the fluoro substituted BCs show the shortest relaxation time of 4.0 h. In the case of fluoro/bromo lateral substituted BCs at terminal azobenzene phenyl ring in 4-methyl resorcinol exhibits longer thermal back relaxation time of ~16.16 h, which is noteworthy. These results envisage the effect of substituents on the central unit as well as the lateral and/or terminal position of azobenzene wings on the photoisomerization. The reversible trans (E) - cis (Z) isomerization occurs in 60 s and 4–16 h, respectively. The prolonged thermal back relaxation attributed to the diazo linkage and the polar substituents. A prototype of optical storage device tested under crossed polarisers at λ = 365 nm, the change from order to disorder state upon illumination with the bright and dark regions was visible and represents ideal candidates for optical storage devices. Compiled results show powerful tuning of structure-property effects using light as external stimuli.