PHOTOCHROMIC BEHAVIOR OF SURFACTANT SPIRO[2H-1-BENZOPYRAN-2,2'[2,3]-DIHYDROINDOLE]S (SPIROPYRANS) ADSORBED INTO CLAY INTERLAYERS

Spiro[2H-1 -benzopyran-2,2'-[2,3]-dihydroindolels (abbreviated as spiropyrans) containing long omega-pyridinoalkyl chains have been intercalated into clay interlayers and studied to observe the photochromic characteristics of the resulting molecular assemblies. 1'-Octadecyl-3',3'-dimethyl-6-nitro-8-pyridinomethyl-(SP1801(+)), 1'-(10-pyridinodecyl)-3',3'-dimethyl-6-nitro- (SP10(+)00) and 1'-(10-pyridinodecyl)-3',3'-dimethyl-6-nitro-8-icosylcarbonyloxymethyl-spiropyrans (SP10(+) 22) were all quantitatively intercalated into the clay interlayer and exhibit normal photochromism in aqueous clay dispersions. Their thermal decolourations obey simple first-order kinetics and are about one-tenth as slow in clay dispersions and about one-hundredth as slow in clay films as that in bulk solution witho ut clay at 50 degrees C. However, 1',3',3 '-trimethyl-6-nitro-8-pyridinomethylspiropyran (SP0101(+)), a homologue without a long alkyl chain, exhibits inverse photochromism and its thermal decolouration undergoes two kinds of first-order kinetics in aqueous clay dispersions. These results are explicable in terms of the restricted conformational motions of the intercalated spiropyrans.