Internal Oriented Electric Fields as a Strategy for Selectively Modifying Photochemical Reactivity

Abstract

Time-dependent density functional theory calculations have been performed on acetophenone derivatives to explore the possibility of using charged functional groups as internal electric fields, the orientation of which can be altered to change photochemical behavior at will. Results demonstrate that nonconjugated charged groups can significantly alter, by up to −1.44 eV, the stabilities of excited states. Specifically, a nonconjugated negatively charged group in the para position will destabilize the nπ* and stabilize the ππ* transitions, while a positively charged group will do the opposite. These electrostatic effects can be tuned by moving these substituents into the meta and ortho positions. Through use of acids and bases, these charged groups can be switched on or off with pH, allowing for selective alteration of the energy levels and photochemical reactivity. Solvent effects are shown to attenuate the electric field effect with increasing dielectric permittivity; however electrostatic effects are shown to remain significant even in quite polar solvents. Using charged functional groups to deliver the position-dependent electrostatic (de)­stabilization effects is therefore a potential route to improving the efficiency of desirable photochemical processes.

Oriented Internal Electrostatic Fields Cooperatively Promote Ground- and Excited-State Reactivity: A Case Study in Photochemical CO2 Capture

“…2,3 However, polarization can also play a key role in enhancing stabilization effects and diminishing destabilization, 30,33 particularly in resonance stabilized systems. In our recent study of Type I photoinitiators, 18 we found that polarization effects were particularly large in ππ* excited states, to the extent that stabilization exceeded 1 eV, while destabilizing effects diminished to almost zero.…”

“…Point charge approximations and σ-induction controls were performed as in our previous studies. 18,30 Scheme 1. Alternative proposed mechanisms for carboxylation of o-alkylphenyl ketones.…”

What Is the Catalytic Mechanism of Enzymatic Histone N‐Methyl Arginine Demethylation and Can It Be Influenced by an External Electric Field?

“…We investigated alternative mechanistic proposals, i.e., C−H or N−H hydrogen abstraction, and explored the effects of long‐range interactions. We also explored the effects of applying an external electric field (EEF) on the reaction mechanism and product selectivity [28b–g] . Comparison of the results for the RDM activity of KDM4E with the KDM activity of KDM4A imply both proceed via ferryl mediated C−H abstraction, but that there are differences in the interactions leading to the formation of intermediates.…”

Electrostatic Perturbations from the Protein Affect C−H Bond Strengths of the Substrate and Enable Negative Catalysis in the TmpA Biosynthesis Enzyme

“…In particular the dipole moment and charge distributions of active site residues affected the C−H bond strengths of the substrate in the binding pocket and triggered a chemoselective reaction mechanism [28] . Experimental studies using electronic absorption methods showed that an external electric field affects charge distributions and influences hydrogen bonding interactions; thereby, moving protons from a donor to an acceptor group or vice versa [29] . To test if something similar would apply to the substrate inside the TmpA enzyme structure, we decided to investigate the C−H bond strengths of the substrate in different environments and under external electric field effects.…”