(Electro)chemical Oxidation of 6,13‐Bis[tri(isopropyl)silylethynyl]pentacene to its Radical Cation and Dication

Abstract

6,13-Bis[tri(isopropyl)silylethynyl]pentacene is a prototypical molecule for organic semiconductor and photovoltaic materials, which makes its electrochemical (redox) properties highly interesting. However, previous cyclic voltammetric studies have provided only limited information. Kinetic and persistence information and identification of the oxidation product(s) and their further reaction or oxidation have not been reported. Thus, an extended electrochemical and spectroscopic investigation of this compound was conducted in CH Cl and THF electrolytes at Pt electrodes. The electrochemically and chemically generated radical cation of the title compound was characterized by using ESR and UV/Vis/NIR spectroscopy and quantum-chemical modeling. In CH Cl , further oxidation to a dication with chemical reversibility at fast timescales but follow-up reactivity at slow timescales was observed. Pertinent parameters of the electron transfers (formal potentials E , electron transfer rate constants k , electron stoichiometry n) were determined. The diffusion coefficients, D, in the two electrolytes were estimated from electrochemical and pulse gradient spin echo (PGSE) NMR spectroscopy data. Simulations of cyclic voltammograms supported the proposed oxidation mechanism and allowed the estimation of further reaction parameters.

Density functional theory and ab initio studies on hyperfine coupling constants of phosphinyl radicals

“…To address this problem we decided to investigate the effect of orbital relaxation for a series of small paramagnetic species, which are commonly used in benchmark computational studies on EPR parameters. [97,98] 17 O for CO + it was found that the unrelaxed density matrix provides a result noticeably closer to the experiment. Regardless of the density matrix, for these three radicals the aforementioned isotropic HFCCs are predicted rather far off the experimental values.…”

“…Among them are electronic (UV/Vis), vibrational (infrared and Raman), nuclear magnetic resonance (NMR), and electron paramagnetic resonance (EPR) spectroscopy. The latter—also called electron spin resonance (ESR) spectroscopy—has proved to be indispensable in studies of radical species, which attract the attention of researchers due to their important roles in physics, chemistry, biochemistry, environmental, and material science …”

Bridging the Gap between Pentacene and Perfluoropentacene: Synthesis and Characterization of 2,3,9,10-Tetrafluoropentacene in the Neutral, Cationic, and Dicationic States

“…A second reduction is not found in the accessible potential window. Apart from this latter observation, the overall electrochemical reaction pattern of F4PEN is, however, similar to that of TIPS-pentacene …”

Photogenerated carrier dynamics of TIPS-pentacene films as studied by photocurrent and electrically detected magnetic resonance

“…Component 2 was a Gaussian line shape with a broad linewidth (∆B1/2=1.8 mT) at g = 2.0022. These g-values are slightly smaller than the value of the TIPS-Pn cation radical in THF solution (g = 2.0025) 44 . It has been reported that the g-value becomes small when the π-orbital of pentacene is perpendicular to the magnetic field.…”

“…The g-value of electron was assumed to be the same as that of free electron (ge = 2.0023), and the g-value of hole was used for the literature value of TIPS-Pentacene cation (gh = 2.0025). 44 There was little Although there is ambiguity regarding the choice of the kinetic constants kS, kT, and k0 because their experimental values are not known, the relative ratios have meaning because the shape of the simulated curves and even the sign of the EDMR depend on those ratios. Under the limitation of k S(T) + kdis = k S(T) + k0 exp(−E/kBT) = 1.5 × 10 7 s −1 (at T = 80 K), 4.3 × 10 7 s −1 (at T = 310 K) < 8.6 × 10 7 s −1 (from linewidth), and kS < kT (the condition to give a negative sign of the EDMR), we chose a proper sets of kS, kT, and k0 values (not a unique solution).…”