Indophenine, known since the late 1800’s, is an intensely colored blue dye consisting of a highly conjugated backbone. Applications of indophenines in organic materials have been limited, however, due to its low solubility and the difficulty in preparing isomerically pure species. As a solution, replacement of thiophene with alkylated 3,4-propylenedioxythiophene (ProDOT) in the synthesis allows for the inclusion of solubilizing side chains and the production of a single isomeric product. Such ProDOT-based indophenines have been shown to possess deep HOMO levels, low-lying LUMO levels, and band gaps of 1.4-1.5 eV. As such, ProDOT-based indophenines offer the promise of useful quinoidal acceptors for incorporation into copolymeric materials. The synthesis of such copolymers via direct arylation polymerization (DArP) will be presented, in which the ProDOT-based indophenine is paired with both traditional donors (i.e. thiophene, ProDOT), as well as the ambipolar unit thieno[3,4-<i>b</i>]pyrazine. Such a polymeric design allows both an increase in quinoidal character and the formation of a complimentary donor-acceptor framework, resulting in a lowering of the polymer band gap to give values of ca. 1.2 eV. Synthesis of the ProDOT-based indophenine, polymerization conditions, and characterization of the resulting copolymeric materials will be presented.

Electronic double dipping: Enhancing the quinoidal character of donor-acceptor frameworks via Indophenine-based acceptors

ACS Spring 2022

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