Dipole-Mediated Rectification of Intramolecular Photoinduced Charge Separation and Charge Recombination

Abstract

Controlling charge transfer at a molecular scale is critical for efficient light harvesting, energy conversion, and nanoelectronics. Dipole-polarization electrets, the electrostatic analogue of magnets, provide a means for "steering" electron transduction via the local electric fields generated by their permanent electric dipoles. Here, we describe the first demonstration of the utility of anthranilamides, moieties with ordered dipoles, for controlling intramolecular charge transfer. Donor− acceptor dyads, each containing a single anthranilamide moiety, distinctly rectify both the forward photoinduced electron transfer and the subsequent charge recombination. Changes in the observed charge-transfer kinetics as a function of media polarity were consistent with the anticipated effects of the anthranilamide molecular dipoles on the rectification. The regioselectivity of electron transfer and the molecular dynamics of the dyads further modulated the observed kinetics, particularly for charge recombination. These findings reveal the underlying complexity of dipole-induced effects on electron transfer and demonstrate unexplored paradigms for molecular rectifiers.

Building blocks for bioinspired electrets: molecular-level approach to materials for energy and electronics

“…1). In addition to determining that these oligomers of aromatic orthoamino acids are indeed molecular electrets [46], we also demonstrated that the Aa dipole rectifies charge transfer [45]. Furthermore, derivatizing an anthranilamide with a secondary amine as R 2 at the 5 th position ( Fig.…”

“…Each Aa residue is added to the sequence as a 2-nitrobenzoic acid derivative [45,46]. A selective reduction of the nitro group to amine prepares the thus added N-terminal residue for the next amide-coupling step [46].…”

“…Using a cyclic secondary amine, i.e. piperidine, requires relatively short reaction times under conventional heating to produce in quantitative yields the nitrobenzoic precursor for the 5Pip residue (Scheme 1a) [45]. In the 4-fluoro-2-nitrobenzoic acid, the C-F bond is not as polarized due to the meta (rather than para) position of the nitro group.…”

“…To address some of the challenges with polypeptide biological and biomimetic structures, we have undertaken a bioinspired approach to designing molecular electrets in the search of properties that are beyond what natural systems can offer [45][46][47][48]. Composed of anthranilamide (Aa) residues, the bioinspired electrets possess ordered amide and hydrogen bonds that, similar to the ordered peptide bonds in protein helices, generate an axial electric dipole (Fig.…”

“…Furthermore, derivatizing an anthranilamide with a secondary amine as R 2 at the 5 th position ( Fig. 1), yields a residue that not only is a good electron donor, but also can host a positive charge for seconds as evident from the reversible electrochemical oxidation [45]. The ability to accommodate positive charges is a promising feature for mediating CT via hole (h + ) hopping.…”