Thermodynamics and mesoscopic organisation in Langmuir monolayers of an azobenzene derivative

► A small change in the chain length dramatically changes the thermodynamic behaviour in monolayers of azobenzene derivatives. ► The presence of the azobenzene moiety has a dramatic impact in the thermodynamics of the phase transition towards a hexatic phase. ► Line tension between the insoluble cis and trans isomers decreases with increasing chain length. ► The capacity to photoalign of 8Az5COOH is similar to the better studied analogue 8Az3COOH.