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

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 trans and cis states were analyzed using surface manometry techniques. The results revealed that NAZ6 molecules in the cis-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 trans-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.