Surface and photochemical properties of Langmuir monolayer and Langmuir–Blodgett films of a spiropyran derivative

Langmuir monolayers of an amphiphilic spiropyran, 1′,3′-dihydro-3′,3′-dimethyl-6-nitro-1′-octadecyl-8-docosanoyloxymethylspiro[1-benzopyran-2,2′-indole] (SP1822) on pure water at 30 °C was investigated by measurements of surface pressure–area (π–A) isotherms and Brewster angle microscopy (BAM). The π–A isotherm shows a phase transition at 7.5 mN m−1. The BAM image reveals drastic morphological changes accompanying the phase transition. Many circular domains appear on uniform monolayers. Atomic force microscopy (AFM) images of as-deposited Langmuir–Blodgett (LB) films suggest that the circular domains consist of bilayers. In addition, monolayers are transformed into bilayers during deposition, which result in the formation of further larger circular domains. Furthermore, the relationship between photochemical property and morphology in the SP1822 LB films was characterized by UV-visible spectroscopy and AFM. We have demonstrated that whether J-aggregates are formed upon irradiation with UV light at room temperature is strongly dependent on the morphology of the SP1822 LB films before irradiation.