Azobenzene derivatives with two aliphatic chains: mesogenic and photoisomerisation studies of (E)-4-[(4-heptyloxyphenyl)diazenyl]phenyl alkanoates (7OABOOCm)

Abstract

ABSTRACT Compounds from the homologous series of (E)-4-[(4-heptyloxyphenyl)diazenyl]phenyl alkanoates (7OABOOCm) for m = 1–19, were synthesised. The phase behaviour was investigated by differential scanning calorimetry, polarised light (optical) microscopy, and thermo-optical analysis. The enantiotropic nematic, smectic C and crystal G phases were found for derivatives with m = 1–18, m = 7–17, and m = 4, respectively. In addition, during cooling, smectic F, crystal G, and unknown X phases were observed for derivatives with m = 7–9, m = 3,8,9, and m = 4, respectively. The X-ray diffraction results suggest that the X phase is presumably monotropic crystal H or a second crystal phase. The E–Z photoisomerisation process was observed during UV light irradiation. A photostationary state was reached after exposure time equal to approximately 80 s. The derived kinetic constant k of this process was of the order of 10−2 s−1.