Preparation and Photochromic Properties of Powder and Films of DNA–Dodecyltrimethylammonium Ion Complex Containing Spiropyran Derivatives

Two thermally reversible photochromic spiropyrans, 1′,3′,3′-trimethyl-6-nitrospiro[2H-1-benzopyran-2,2′-indoline] 1 and 3′,3′-dimethyl-6-nitro-1-(3-sulfopropyl)spiro[2H-1-benzopyran-2,2′-indoline] triethylamine salt 2, were incorporated in powder and films of an organic-solvent-soluble DNA–dodecyltrimethylammonium ion complex. The powder and the films showed thermally reversible photochromism. The spiropyrans in the powder were considered to be intercalated into the DNA base pairs because: 1) they were thoroughly washed to remove weakly attaching molecules and 2) the color of the powder was different from either of the closed or open forms of the spiropyran, whereas spiropyrans doped in the films behaved as in the polar organic solvents, so that the film was a mixture of spiropyran and the DNA–dodecyltrimethylammonium ion complex.