Photochromism of spiropyrans in polyion complex cast films: formation of stable aggregates of photo-merocyanines

Abstract

Photochromism of a series of 1′-alkyl(R 1)-3′,3′-dimethyl-6-nitro-8-alkanoyloxymethyl(R 2)-spiro(2H-1-benzopyran-2,2′-indoline) derivatives (SPs) having different length of alkyl chains are investigated in AOT-poly(diallyldimethylammonium) or dialkyldimethylammonium-poly(styrenesulphonate) polyion complex cast films. It has been shown that SPs bearing two long alkyl chains form stable aggregates of photomerocyanines (PMC) when irradiated in the cast film. Thus, SP- 3 (R 1 = C 18H 37, R 2 = CH 2OCOC 11H 23) generates H-aggregated PMC while SP- 4 (R 1 = C 18H 37, R 2 = CH 2OCOC 21H 43) forms J-PMC. Factors controlling aggregate formation are discussed.