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Design and Charge-Transfer Properties of Bioinspired Electrets

  • Author(s): Bao, Duoduo
  • Advisor(s): Vullev, Valentine I
  • et al.

In order to develop and demonstrate fundamental strategies for improving the efficiency of photovoltaic devices that are commonly used for solar-energy capture and conversion, we introduced and studied anthranilamides as bioinspired electrets.

Charge transfer processes play a key role in chemical and biological systems. Photoinduced charge transfer represents the central paradigm of light-energy conversion of photosynthesis and photovoltaic devices. The Rehm-Weller equation allows for estimating the diving force of photoinduced charge transfer by employing readily measureable quantities such as the redox potentials and spectroscopic data of electron donors and acceptors. A significant part of my studies focused on the Born solvation term in the Rehm-Weller equation that introduces the electrostatic stabilization of the charge-transfer species by the surrounding media. Cyclic voltammetry, allowed me to demonstrate experimentally the effects of the supporting electrolyte on the redox potentials. These effects were especially pronounced for non-polar solvents. Most importantly, I devised an approach to address the discrepancies that the presence of electrolyte introduces to the charge-transfer analysis. Concurrently, my studies demonstrated that the Generalized Born model allows for addressing the deficiencies in the charge-transfer analysis involving redox species that are not spherical and that have heterogeneous charge distribution.

The other significant part of my studies focused on anthranilamides as bioinspired electrets that have the potential to accelerate charge separation and suppress the undesired charge recombination. My research provided the first experimental demonstration that the anthranilamides possess intrinsic dipoles. These amides with large intrinsic dipole moments (that is, electrets) can generate electric field, which enhances electron transfer from their N- to their C-termini and impedes it in the backward direction. To test the ability of the electrets to modify the direction of electron transfer, I incorporated an anthranilamide monomer in electron donor-acceptor (DA) dyads. Comparison between the charge-transfer kinetics of electret-acceptor dyads, revealed a faster initial photoinduced charge separation and a slower charge recombination when electron was transferred toward C-terminus. These findings were consistent with the orientation of the intrinsic dipole moment of the anthranilamide monomer. Aside from previous work employing polypeptides, this is the first demonstration of rectification of charge transfer by dipole moments of synthetic bioinspired derivatives.

In summary, the most important contributions from my doctoral work were: (1) developing methods for reliable interpretation of experimental results pertinent to charge-transfer kinetics and thermodynamics; (2) demonstrating rectification of photoinduced charge transfer induced by the anthranilamide intrinsic dipole; and (3) demonstrating that the photoinduced processes result in charges residing on the anthranilamides (i.e., radical ions) which is essential for attaining hopping mechanism for long-range charge transfer.

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