Dipole Effects on Electron Transfer are Enormous

Abstract

Molecular dipoles present important, but underutilized, methods for guiding electron transfer (ET) processes. While dipoles generate fields of Gigavolts per meter in their vicinity, reported differences between rates of ET along versus against dipoles are often small or undetectable. Herein we show unprecedentedly large dipole effects on ET. Depending on their orientation, dipoles either ensure picosecond ET, or turn ET completely off. Furthermore, favorable dipole orientation makes ET possible even in lipophilic medium, which appears counterintuitive for non-charged donor-acceptor systems. Our analysis reveals that dipoles can substantially alter the ET driving force for low solvent polarity, which accounts for these unique trends. This discovery opens doors for guiding forward ET processes while suppressing undesired backward electron transduction, which is one of the holy grails of photophysics and energy science.

How Do Amides Affect the Electronic Properties of Pyrene?

“…The effects are, indeed, more pronounced when the amide is directly attached via its nitrogen than its carbonyl carbon. Also, the close resemblance between the properties of Py mN-C and Py mC-N indicates that the amide electric dipoles, which generate large fields even across methylene linkers, 39 are not responsible for the observed effects. The lack of a significant solvent dependence of and Δν (Table 1) further confirms that amide dipoles do not contribute to the differences between the photophysics of the four derivatives.…”

“…22−32 In addition to making ion channels functional, 17,33 such dipolar amide conjugates prove invaluable for rectifying the directionality of electron transfer and transport. 21,34−39 Aliphatic amides oxidize at about 1.5 V versus saturated calomel electrode (SCE) 40 and have optical gaps of 5.6 eV between their highest occupied molecular orbitals (HOMOs) and lowest unoccupied molecular orbitals (LUMOs), corresponding to an n−π* transition around 222 nm, 11 making them electron-rich π-conjugated UV absorbers.…”

A Full‐Spectrum Metal‐Free Porphyrin Supramolecular Photocatalyst for Dual Functions of Highly Efficient Hydrogen and Oxygen Evolution

“…First, due to dipole‐induced potential difference, a built‐in electric field is formed in SA‐TCPP . The built‐in electric field will be enhanced with the increase of the molecular dipole, accordingly promoting the separation of the photogenerated hole–electron pair . As shown in Figure a–c, the photocatalytic activities are positively correlated with molecular dipoles.…”

Highly Polarized Coumarin Derivatives Revisited: Solvent‐Controlled Competition Between Proton‐Coupled Electron Transfer and Twisted Intramolecular Charge Transfer

“…In our dyads, the final state is the optically dark CT state, so this parameter cannot be directly observed. Electrochemical potentials depend on the solvent, and for single‐electron oxidation or reduction their values in solvents i and j with static dielectric constants ϵ i and ϵ j are related by the simplified formula [Eq. ]: …”

“…The theoretical basis for ET processes was originally established in the seminal works of Marcus and Weller more than half a century ago. The kinetics and thermodynamics of the ET process are both modulated by the electrochemical and excited‐state properties of molecular systems, with accompanying structural changes, which proceed in competition with radiative and radiationless deactivation processes …”