Alcohol-soluble bis(tpy)thiophenes: new building units for constitutional dynamic conjugated polyelectrolytes

Abstract

New building units (unimers) for metallo-supramolecular polymers 2,5-bis(2,2′:6′,2′′-terpyridine-4′-yl)thiophene, M, and 5,5′-bis(2,2′:6′,2′′-terpyridine-4′-yl)(2,2′-bithiophene), B, with ionic groups attached to thiophene rings are prepared by the modification of corresponding bromo-precursors and assembled with Zn²⁺ and Fe²⁺ ions into alcohol-soluble conjugated constitutional-dynamic polyelectrolytes (polyelectrolyte dynamers). Ionization of side groups only slightly affects the absorption spectra of unimers as well as dynamers but dramatically changes their solubility. Cyclic conformations of unimer molecules resulting from intramolecular interactions between tpy end-groups and cationic or polar (–CH₂Br) side groups are proposed to explain the spectral conformity of the M- and B-type unimers and their dynamers and also inhibition of the ionization reaction with tpy end-groups. The absorption spectra and excitation profiles of Raman spectra show that mainly the red arm of the metal-to-ligand charge transfer band of Fe-dynamers is significantly contributed with transitions involving thiophene rings. The constitutional dynamics of Zn-dynamers is fast while that of Fe-dynamers is so slow that it allows effective separation of the dynamer to fractions in SEC columns. Electronic spectra and viscosity measurements proved that excess of Fe²⁺ ions results in shortening of the dynamer chains and their end-capping by these ions.