Polarons, Bipolarons, and π-Dimers of Bis(3,4-ethylene-dioxythiophene)-(4,4‘-dialkyl-2,2‘-bithiazole)- co-Oligomers. Direct Measure of the Intermolecular Exciton Transfer Interaction

The oxidative behavior of bithiazole-ethylenedioxythiophene co-oligomers is described. The acceptor−donor−acceptor (A−D−A) compounds, 5,5‘-bis(4,4‘-dialkyl-2,2‘-bithiazol-5-yl)-(3,4,3‘,4‘-bis(ethylenedioxy)-2,2‘-dithienyl) ( 1, 2 ), are sequentially oxidized by NOBF 4 through the paramagnetic monocation to the diamagnetic dication. The monocations form diamagnetic π-dimers, the allowed π−π electronic transitions of which are interpreted in terms of molecular exciton theory to give nearest-neighbor exciton coupling constants, J ≅ 0.2 eV. The spectra of the dications show that they are bipolarons; that is, the two charges share a common lattice deformation. The D−A−D co-oligomers, 5,5‘-bis(3,4-ethylenedioxythien-2-yl)-4,4‘-dibutyl-2,2‘-bithiazole ( 3 ) and 5,5‘-bis(3,4,3‘,4‘-bis(ethylenedioxy)-2,2‘-dithien-5-yl)-4,4‘-dibutyl-2,2‘-bithiazole ( 4 ), are oxidized in a single step to the corresponding bipolarons.