Photoinduced self-assembly of the supramolecular photochromic systems – photoinduced dimer formation of the inclusion complexes of an indolinospiropyran with CDs

The photochromic spiropyran with a long alkyl chain can form inclusion complexes with cyclodextrins (CDs) in aqueous solution. The complexes are axial inclusion complexes formed between the long alkyl chain and CDs, with the spiropyran head group located outside the cavities of CDs. Under UV irradiation, the inclusion complexes show normal photochromism. The coloured form(B) of the complexes can assemble into a dimer. Unlike the dimer formed in apolar solvents or in polymers, which consists of a coloured molecule (B) and a colourless molecule (A) with a composition of AB, the dimer consists of two coloured molecules (B) in the present system. Corresponding to its structure, the decolouration process can not be described by an exponential or a two-exponential kinetics, but obeys half-order kinetics very well.