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.