Photosensitive Monolayers. Studies of Surface-Active Spiropyrans at the Air-Water Interface

Article abstract of DOI:10.1021/j150648a020

The influence of light on the spreading behavior of three long-chain spiropyrans at the air-water interface was investigated.Two compounds were insufficiently polar to spread on the surface of water in the dark and were unstable with respect to crystallization.On 3-5 min of 254-nm irradiation, however, the dispersions spread reproducibly on the surface to give monolayers with typical collapse pressures of 32 mN/m at 0.38 nm²/molecule.Irradiated monolayers of one of the compounds, a thioindolinospiropyran, had high thermal stability.On the other hand, irradiated monolyers of 3'3'-dimethyl-1'-hexadecyl-6-nitrospiro<2H-1-benzopyran-2,2'-indoline> (I) revert completely to the surfac-inactive starting material by a thermal reaction the a large temperature coefficient.The apparent first-order decay constants for decrease of the surface pressure of I increased from 1.7E-5 s^-1 at 11.0 deg C to 5.4E-3 s^-1 at 46.0 deg C, corresponding to an apparent "activation energy" of 144 kJ/mol.