Charged states in diphenylamino endcapped thiophenes with a 1,4-phenylene core: In situ electron spin resonance/ultraviolet–visible–near infrared and nuclear magnetic resonance spectroelectrochemistry and quantum chemical study

Abstract

The three diphenylamino-endcapped thiophene compounds 1,4-bis-(2-diphenylamino-thiophen-5-yl)-benzene (A), 1,4-bis-[2-(phenothiazin-10-yl)-thiophen-5-yl]-benzene (B), and 1,4-bis-(5-diphenylamino-[2,2′]bithiophen-5′-yl)-benzene (C) with a central phenylene core were investigated by in situ ESR/UV–vis–NIR and in situ NMR spectroelectrochemistry and quantum chemical studies. The computed vertical ionization potentials are 4.85eV for A, 5.39eV for B and 4.80eV for C while the adiabatic ionization potentials are slightly lower 4.45eV (for A), 4.96eV (for B) and 4.47eV (for C). The minimal difference between computed ionization potentials of A and C and the lower oxidation ability of B are in good agreement with the experimental electrochemical findings with the first half-wave anodic potentials 0.69V (for A), 0.81V (for B) and 0.67V (for C), all vs. decamethylferrocene (DmFc+/DmFc). For the radical monocations A+ and C+ the spin delocalisation on the central phenylene moiety was confirmed both experimentally and by theoretical calculations. For the radical cation B+, the presence of a phenothiazinyl moiety is responsible for the delocalization of unpaired electron in the lateral part of this molecule. The stability of the charged states was increased substantially by the incorporation of two further 2,5-thienylene moieties between the central moiety and the side groups in C. Detailed spectroelectrochemical studies of the cation radical, dication, trication and tetracation of C are in good agreement with the calculated electronic transitions and experimental values for all redox states. In situ NMR spectroelectrochemical studies at different temperatures indicate dimerisation reactions of charged 1,4-bis-(5-diphenylamino-[2,2′]bithiophen-5′-yl)-benzenes.