A study on the thermo-photoisomerization of a liquid crystalline dimer of cyanoazobenzene and naphthalene.

Rabari, Mahima; Prajapati, A K; Mahesha, S; Akshaya, M K; Kumar, Bharat · Soft Matter · 2025

basic_science · Level V

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Abstract

The isomerization kinetics of a liquid crystalline azobenzene dimer, comprising cyanoazobenzene and naphthalene (NAZ6), were investigated at the air-water interface. The Langmuir monolayers of NAZ6 in both its <i>trans</i> and <i>cis</i> states were analyzed using surface manometry techniques. The results revealed that NAZ6 molecules in the <i>cis</i>-state displayed the coexistence of a disordered liquid-expanded phase and an ordered liquid-condensed phase, whereas no such phase transition was observed in the <i>trans</i>-state. Intriguingly, below the temperature of 303 K, the surface pressure decreased during photoisomerization and above the temperature of 303 K the surface pressure increased during photoisomerization. This anomalous phenomenon is attributed to the unique molecular structure of NAZ6, which features two azobenzene moieties, influencing its isomerization dynamics and interfacial properties.