The most commonly applied approach to the generation of low bandgap (Eg &lt; 1.5 eV) and reduced bandgap (Eg = 1.5-2.0 eV) conjugated polymers is via the utilization of a donor-acceptor (D-A) framework. Such frameworks employ a backbone of alternating electron-rich and electron-deficient moieties in order to produce a hybrid material with HOMO levels characteristic of the donor and LUMO levels characteristic of the acceptor, thus resulting in a reduced HOMO-LUMO energy and lower bandgap. The widespread application of such frameworks has since led to a number of assumptions and misconceptions in the literature, the most basic of which is that monomeric units act exclusively as donors, acceptors, or neutral spacers. At odds with this assumption, however, is the recent knowledge that the commonly applied class of acceptors, thieno[3,4-b]pyrazines (TPs) also exhibit properties of very strong donors comparable to 3,4-ethylenedioxythiophene, leading to the use of the term ambipolar units to describe these building blocks. As TPs exhibit a high-lying HOMO, this should allow for a new design model in which ambipolar TP units are paired with an acceptor, rather than the traditional pairing with a donor. Several such ambipolar-acceptor frameworks have now been successfully produced via direct arylation polymerization to give materials with bandgaps of 0.97-1.12 eV. The synthesis of such ambipolar-acceptor frameworks will be presented along with their optical and electronic characterization. Furthermore, the potential broader applications of this new design paradigm will also be discussed.

Going against the grain: A new design paradigm for low bandgap polymers

ACS Spring Meeting 2021

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