3 TYPES OF AGGREGATES OF SPIROPYRAN WITH LONG AND SHORT HYDROPHOBIC ALKYL CHAINS

The spiropyran derivative 1'-octadecyl-3',3'-dimethyl-6-nitro-8-ethoxymethyl-spiro[2H-1-benzopyran-2,2'-indoline] (SP1802) has been synthesized and its photochromic and aggregate forming properties in both monolayer films at the air-water interface and in Langmuir-Blodgett (LB) films have been investigated. The UV-induced photomerocyanine (PMC) isomer forms J-aggregates (lambda(max) = 655 nm) on the water surface when compressed. In the LB deposition process a rapid transfer rate induces a change to the brickwork-like arrangement of the chromophores in the J-aggregates, and H-aggregates (lambda(max) = 495 nm) and I (intermediate)-aggregates (lambda(max) = 575 nm) form depending on the surface pretreatment of the substrate. Hydrophobic substrates treated with trimethylchlorosilane, yield a change to the H-aggregates whilst substrates precoated with multilayers of arachidic acid produce a change to the I-aggregates.