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© 2015 Society of Photo-Optical Instrumentation Engineers (SPIE). The diversity of life on Earth is made possible through an immense variety of proteins that stems from less than a couple of dozen native amino acids. Is it possible to achieve similar engineering freedom and precision to design electronic materials? What if a handful of nonnative residues with a wide range of characteristics could be rationally placed in sequences to form organic macromolecules with specifically targeted properties and functionalities? Referred to as molecular electrets, dipolar oligomers and polymers composed of non-native aromatic beta-amino acids, anthranilamides (Aa) provide venues for pursuing such possibilities. The electret molecular dipoles play a crucial role in rectifying charge transfer, e.g., enhancing charge separation and suppressing undesired charge recombination, which is essential for photovoltaics, photocatalysis, and other solar-energy applications. A set of a few Aa residues can serve as building blocks for molecular electrets with widely diverse electronic properties, presenting venues for bottom-up designs. We demonstrate how three substituents and structural permutations within an Aa residue widely alter its reduction potential. Paradigms of diversity in electronic properties, originating from a few changes within a basic molecular structure, illustrate the promising potentials of biological inspiration for energy science and engineering.

In biology, an immense diversity of protein structural and functional motifs originates from only 20 common proteinogenic native amino acids arranged in various sequences. Is it possible to attain the same diversity in electronic materials based on organic macromolecules composed of non-native residues with different characteristics? This publication describes the design, preparation and characterization of non-native aromatic β-amino acid residues, i.e. derivatives of anthranilic acid, for polyamides that can efficiently mediate hole transfer. Chemical derivatization with three types of substituents at two positions of the aromatic ring allows for adjusting the energy levels of the frontier orbitals of the anthranilamide residues over a range of about one electronvolt. Most importantly, the anthranilamide residues possess permanent electric dipoles, adding to the electronic properties of the bioinspired conjugates they compose, making them molecular electrets.