Langmuir‐blodgett films of photochromic polyglutamates, 7. The photomechanical effect in monolayers of polyglutamates with azobenzene moieties in the side chains

Monolayers of the photochromic hairy‐rod type polymers poly(5‐[2‐[4‐(4‐hexylphenylazo)‐phenoxy]ethyl]‐L‐glutamate) (1) and poly(5‐(2‐[4‐(4‐decyloxyphenylazo)phenoxy]ethyl)‐L‐glutamate) (2) were investigated at the air/water interface. At constant surface pressure the monolayers of the polymers exhibit a reversible expansion upon irradiation with ultraviolet (UV)‐light, due to the photoinduced E‐Z‐isomerization of the azobenzene chromophore and a concomitant restructuring of the monolayer. The area increase is lower than expected from the isotherms of monolayers spread from irradiated and non‐irradiated solutions. This can be attributed to a hindrance of photoisomerization, as proved by UV/Vis spectroscopic investigations. The hindrance of photoisomerization, and the photomechanical effect depend on temperature, surface pressure and the nature of the polymer, which all influence the flexibility of the monolayer. From a comparison of the isomerization rate and the rate of the photomechanical effect a two‐step mechanism for the monolayer restructuring is deduced.