Abstract
Photoreactions and aggregation of spiropyran with a long alkyl chain (SP98) were studied by surface reflection spectroscopy at the air-water interface. SP98 in mixtures with arachidic acid formed stable monolayers on pure water or on a subphase containing Cd2+. Colored photomerocyanine (PMC98) was formed at the air-water interface by UV-irradiation. The reflection peak of PMC98 shifted from 545nm to 618nm with increasing surface pressure on a subphase containing Cd2+. The latter corresponded to the peak of aggregates observed in non-polar solutions. PMC98 formed J-like aggregates at surface pressures above 10-20mN m-1 on the subphase containing Cd2+, but hardly formed them on pure water. The back reaction from PMC98 to SP98 upon visible irradiation depended on the surface pressure and the subphase. About 36% of aggregated PMC98 remained even after 90min at 30mN m-1, while at 10 and 1.5mN m-1 PMC98 converted completely to SP98 within 20 and 10min, respectively.
