CONTROLS OF NOVEL PHOTOCHROMIC BROMOSPIROPYRAN AGGREGATES

The photochromism of amphiphilic dibromospiropyrans, 5',7'-dibromo-8-docosanoyloxy-methyl-3',3'-dimethyl-6-nitro-1'-octadecylspiro[2 H-1-benzopyran-2,2'-indoline] BSP 1822, in polyion complexes and Langmuir-Blodgett (LB) films has been studied. The colored BSP1822 forms J-aggregate when mixed with polyion complexes between dioctadecyldimethylammonium salt of poly(styrene sulfonate) and some amphiphilic compounds such as methyl stearate. The J-aggregate is also formed in polyion complexes with other amphiphilic compounds which have melting point around 40-degrees-C. It is considered that these compounds play a role in enforcing interaction amoung chromophores and lowering the glass transition temperature. The similar behavior was also found for the BSP1822 LB film mixed with dioctadecyldimethylammounium bromide and methyl stearate. The absorption maximum of J-aggregated BSP1822 is 650 nm, which is 32 nm longer than that of spiropyran without bomide. The J-aggregate exhibits exceedingly high stability in retaining its color, which is in marked contrast to the rapidly fading nonaggregated chromophore.