Controlling charge transfer at nanometer scale is a critical component of efficient light harvesting and energy conversion. Because local electric fields provide a means for �steering� electron transduction, molecular electrets present an important paradigm for energy science and engineering. An �electret,� or specifically, a �dipole-polarization electret,� is an electrostatic analogue of a magnet. An electret contains co-directionally ordered permanent electric dipoles. Dipolar films, or layers of molecular electrets, for example, rectify interfacial charge transfer and provide a means for improving the efficiency of photovoltaic devices. While it is paramount for the electrets to be dielectrics (free charge carriers will screen the fields generated by the intrinsic dipoles), tuning their redox properties provides a means for attaining electron or hole transduction through them. We undertake a bioinspired approach in the design of molecular electrets that is based on anthranilamides, i.e., oligomers composed of derivatives of vitamin L1, or any ortho-aminobenzoic or 2-naphthoic acid (Figure 1). We have demonstrated that similar to protein helices, the anthranilamides possess intrinsic dipoles originating from ordered amide and hydrogen bonds. Unlike their biological counterparts, however, the bioinspired molecular electrets have extended p-conjugation along their backbones providing a means for efficient charge transfer. These molecular electrets, indeed, rectify the kinetics of charge separation. The rates of electron transfer along the electret dipoles were faster than the rates against the dipoles. (The direction of the dipoles is defined from their negative to their positive poles.) For processes with small driving forces, the modulation of the energies of the charge-transfer states accounts for the observed rectification trends. Conversely, the same explanation could not account for the observed rectification of charge recombination. Molecular dynamics and conformation gating proved to prevail the charge-recombination kinetics. These mechanistic findings provide unexplored paradigms and venues for energy-conversion applications. Figure 1.  Bioinspired molecular electrets.

Bioinspired electrets for solar-energy conversion

247th National Meeting (2014)

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