pH-Controlled reversible formation of a supramolecular hyperbranched polymer showing fluorescence switching

A π-conjugated AB2 monomer 1 with a dibenzo[24]crown-8 (DB24C8) ring and two secondary amine centres has been synthesised. Treatment of a solution of 1 in dichloromethane with trifluoroacetic acid (TFA) leads to protonation of the amine groups, and then the DB24C8 rings are threaded by the dialkylammonium ion centres of other monomer molecules, leading to the formation of a supramolecular hyperbranched polymer, TFA-1. Rather strong π-π stacking interactions between the conjugated cores are evident in this polymer. The supramolecular hyperbranched polymer (SHP) can be completely depolymerised by adding a slight excess of N-tert-butyl-N',N',N'',N'',N''',N'''-hexamethylphosphorimidic triamide, tetrabutylammonium fluoride, or tetrabutylammonium acetate. The acid-base-controlled process induces a reversible change in the fluorescence intensities of the solutions due to the controllable presence of the π-π stacking interactions between the conjugated cores. This dynamic behaviour is significant with respect to "smart" supramolecular polymer materials.