Fractional charge density functional theory elucidates electro-inductive and electric field effects at...

Area of Science:

• Computational Chemistry
• Surface Science
• Electrochemistry

Background:

• External voltages dynamically tune molecular properties in self-assembled monolayers on electrodes.
• Applied voltage induces electro-inductive and electric field effects, altering molecular chemical properties and reactivity.

Purpose of the Study:

• To present a novel computational method, fractional charge density functional theory plus a model electrode and continuum solvent (FC-DFT+).
• To offer quantitative insights into electro-inductive and electric field effects at electrochemical interfaces.
• To elucidate the distinct contributions of these effects to molecular property tuning.

Main Methods:

• Utilized fractional charge density functional theory (FC-DFT+) coupled with a model electrode and continuum solvent model.
• Applied FC-DFT+ to analyze nitrile frequency shifts and Lewis adduct formation.
• Investigated the voltage dependence of molecular properties and ionic strength effects.

Main Results:

• FC-DFT+ accurately predicts C≡N frequency vs. voltage slopes, frequency flattening, and ionic strength dependence.
• Frequency flattening is attributed to electro-inductive effects, especially near the HOMO-LUMO gap.
• Electro-inductive effects dominate nitrile frequency shifts, while electric field effects play a smaller, opposing role.
• FC-DFT+ confirms electro-inductive effects in NO2 stretching frequency flattening and electric field effects in Lewis adduct formation.

Conclusions:

• FC-DFT+ is a versatile tool for quantitatively predicting electro-inductive and electric field effects.
• Electro-inductive and electric field effects have distinct and significant impacts on molecular properties and reactivity.
• This methodology can guide diverse chemical applications at electrochemical interfaces.