Bridge- and solvent-mediated intramolecular electronic communications in ubiquinone-based biomolecular wires

Abstract

Intramolecular electronic communications of molecular wires play a crucial role for developing molecular devices. In the present work, we describe different degrees of intramolecular electronic communications in the redox processes of three ubiquinone-based biomolecular wires (Bis-CoQ0s) evaluated by electrochemistry and Density Functional Theory (DFT) methods in different solvents. We found that the bridges linkers have a significant effect on the electronic communications between the two peripheral ubiquinone moieties and solvents effects are limited and mostly depend on the nature of solvents. The DFT calculations for the first time indicate the intensity of the electronic communications during the redox processes rely on the molecular orbital elements VL for electron transfer (half of the energy splitting of the LUMO and LUMO+1), which is could be affected by the bridges linkers. The DFT calculations also demonstrates the effect of solvents on the latter two-electron transfer of Bis-CoQ0s is more significant than the former two electrons transfer as the observed electrochemical behaviors of three Bis-CoQ0s. In addition, the electrochemistry and theoretical calculations reveal the intramolecular electronic communications vary in the four-electron redox processes of three Bis-CoQ0s.

Figure 1. Structures of three Bis-CoQ₀s in the research.

Figure 2

(A) CV curves of 1.0 mM CoQ₀, Bis-CoQ₀ 1, Bis-CoQ₀ 2 and Bis-CoQ₀ 3 obtained at a GC electrode (ø = 3 mm) in anhydrous and deoxygenated CH₃CN containing 0.1 M TBAP at scan rate 0.100 Vs⁻¹; (B) experimental (black line) and simulated (colored) DPV curves of 1.0 mM CoQ₀, Bis-CoQ₀ 1, Bis-CoQ₀ 2 and Bis-CoQ₀ 3, increment E = 0.004 V, frequency = 15 Hz.

Figure 3

The energies of the frontier molecular orbitals (LUMO-1, black lines; LUMO, red lines; HOMO, blue lines; HOMO-1, pink lines) of three Bis-CoQ₀s and their corresponding electronic density contours for neutral and different charge species in four electrons transfer processes.

Figure 4

CV and DPV curves of 1.0 mM Bis-CoQ₀ 1 (A and B), Bis-CoQ₀ 2 (C and D) and Bis-CoQ₀ 3 (E and F) obtained at a glassy carbon electrode in distilled THF (black line), CH₂Cl₂ (red line), CH₃CN (blue line), DMF (orange line) and DMSO (pink line) containing 0.1 M TBAP at scan rates 0.010 Vs⁻¹.

Figure 5

The scatter diagram of experimental vs. calculated reduction potentials for four electrons transfer processes of Bis-CoQ₀ 1 (A) and Bis-CoQ₀ 2 (B) in five aprotic solvents.