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    Photoinduced modulation of refractive index in Langmuir-Blodgett films of azo-based H-shaped liquid crystal molecules

    Year: 2022

    Journal: J. Mol. Liq., Volume 364, OCT 15

    Authors: Joshi, Ashutosh; Gayakwad, Akash; Manjuladevi, V.; Varia, Mahesh C.; Kumar, S.; Gupta, R. K.

    Organizations: SERB [CRG/2018/000755]; DST India; IDP [IDP/SEN/06/2015]

    Keywords: Langmuir-Blodgett (LB) films; Trans-cis transformation; Refractive index; Surface plasmon resonance (SPR); Photoinduced

    The development of optically active area consisting of organic molecules are essential for the devices like optical switches and waveguides, as it can be easily maneuvered by the application of suitable electro-magnetic (EM) waves. In this article, we report the development of a photoactive surface by the deposi-tion of a single layer of Langmuir-Blodgett (LB) film of a novel H-shaped liquid crystal (HLC) molecule. The synthesized HLC molecules possess azo-groups and nitro-groups. The azo-group can be isomerized (trans-cis transformation) by irradiating them with ultraviolet (UV) light. The nitro-group can provide sufficient amphiphilicity to the HLC molecules to form a stable Langmuir monolayer at air-water inter-face. The Langmuir monolayer of the HLC molecules exhibited gas and liquid-like phases. A single layer of LB film of HLC molecules was deposited on a gold chip of a home-built surface plasmon resonance (SPR) instrument. The azo-groups of the molecules in LB film was excited by UV irradiation leading to a change in morphology due to trans-cis transformation. Such a change in morphology can lead to a miniscule change in refractive index (RI) of the LB film. SPR is a label free and highly sensitive optical phenomenon for the measurement of such changes in RI. In our studies, we found systematic changes in the resonance angle of the LB film of HLC molecules as a function of intensity of the UV irradiation. We measured switch-on and switch-off intensity which may suggest that the LB film of HLC molecules can find appli-cations in optical switches or waveguides.(c) 2022 Elsevier B.V. All rights reserved.
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