Sequence Matters: Determining the Sequence Effect of Electronic Structure Properties in π-Conjugated Polymers. In: Lutz J, Meyer TY, Ouchi M, Sawamoto M, editors. Sequence-Controlled Polymers: Synthesis, Self-Assembly, and Properties. Washington: American Chemical Society; 2014. pp. 379-93. [DOI: 10.1021/bk-2014-1170.ch025]

Computational Evolution of High-Performing Unfused Non-Fullerene Acceptors for Organic Solar Cells

Materials optimization for organic solar cells (OSCs) is a highly active field, with many approaches using empirical experimental synthesis, computational brute-force approaches to screen candidates in a given subset of chemical space, or generative machine learning methods which often require significant training sets. While these methods may find high-performing materials, they can be inefficient and time-consuming. Genetic algorithms (GAs) are an alternative approach, allowing for the "virtual synthesis" of molecules and a prediction of their ``fitness' for some property, with new candidates suggested based on good characteristics of previously generated molecules. In this work, a GA is used to discover high-performing unfused non-fullerene acceptors (NFAs) based on an empirical prediction of power conversion efficiency (PCE) and provides design rules for future work. The electron withdrawing/donating strength, as well as the sequence and symmetry of those units are examined. The utilization of a GA over a brute force approach resulted in speedups up to $1.8 \times 10^{12}$. New types of units not frequently seen in OSCs are suggested, and in total 5,426 NFAs are discovered with the GA. Of these, 1,087 NFAs are predicted to have a PCE greater than 18\%, which is roughly the current record efficiency. While the symmetry of the sequence showed no correlation with PCE, analysis of the sequence arrangement revealed that higher performance can be achieved with a donor core and acceptor end groups. Future NFA designs should consider this strategy as an alternative to the current A-D-A$'$-D-A architecture.

Stereo-, Temporal and Chemical Control through Photoactivation of Living Radical Polymerization: Synthesis of Block and Gradient Copolymers

Nature has developed efficient polymerization processes, which allow the synthesis of complex macromolecules with a perfect control of tacticity as well as molecular weight, in response to a specific stimulus. In this contribution, we report the synthesis of various stereopolymers by combining a photoactivated living polymerization, named photoinduced electron transfer-reversible addition-fragmentation chain transfer (PET-RAFT) with Lewis acid mediators. We initially investigated the tolerance of two different photoredox catalysts, i.e., Ir(ppy)3 and Ru(bpy)3, in the presence of a Lewis acid, i.e., Y(OTf)3 and Yb(OTf)3, to mediate the polymerization of N,N-dimethyl acrylamide (DMAA). An excellent control of tacticity as well as molecular weight and dispersity was observed when Ir(ppy)3 and Y(OTf)3 were employed in a methanol/toluene mixture, while no polymerization or poor control was observed with Ru(bpy)3. In comparison to a thermal system, a lower amount of Y(OTf)3 was required to achieve good control over the tacticity. Taking advantage of the temporal control inherent in our system, we were able to design complex macromolecular architectures, such as atactic block-isotactic and isotactic-block-atactic polymers in a one-pot polymerization approach. Furthermore, we discovered that we could modulate the degree of tacticity through a chemical stimulus, by varying [DMSO]0/[Y(OTf)3]0 ratio from 0 to 30 during the polymerization. The stereochemical control afforded by the addition of a low amount of DMSO in conjunction with the inherent temporal control enabled the synthesis of stereogradient polymer consisting of five different stereoblocks in one-pot polymerization.