The Role of Heteroatoms Leading to Hydrogen Bonds in View of Extended Chemical Stability of Organic Semiconductors

Abstract

The major challenge in organic electronics concerns the stability of organic semiconductor materials which affects the operational lifetime of devices. Recent reports have shown that hydrogen‐bonded pigments of the indigoid family are air‐ and moisture resistant. The magenta pigment quinacridone, a hydrogen‐bonded molecule in the solid state with a pentacene like frame, is a perfect example for extraordinary chemical stability. Here, studies using in situ spectroscopic methods comparing quinacridone and pentacene are presented. A different spectral response of their radical cations is observed upon chemical doping. While in pentacene the barrier between doping and irreversible overoxidation is small, this stability toward overoxidation is increased by the heteroatomic structure, leading to hydrogen‐bonded quinacridone. This work provides insight into molecular design principles that may lead to next‐generation organic semiconductors with enhanced stability and performance.

An Anthraquinone/Carbon Fiber Composite as Cathode Material for Rechargeable Sodium‐Ion Batteries

“…A potential difference upon reaction with Na + ‐ions between galvanostatic charge/discharge cycles (Figure a) is frequently observed and may be attributed to a kinetic effect. This kinetic effect is known to be mainly governed by the ohmic and diffusion resistance of the organic material ,. To gain further insights into the ohmic and diffusion resistances, impedance spectra (EIS) are recorded at different, selected potentials, in the frequency range between 100 kHz and 10 mHz, with 10 mV AC amplitude.…”

“…While R e ct can be easily determined by the intersect of the first semi-circle in the Nyquist plots with the x-axis (Re(Z) in W), the Warburg diffusion is determined by plotting the real impedance part vs. the square root of the angular frequency (w À1/2 ). The slope of the linear part between the two semicircles ( Figure S7) allows then to determine the Warburg coefficient (A w ), which is related to the diffusion coefficient D according to Equation (1): [44] D ¼…”

Spectroscopic characterization of charge carriers of the organic semiconductor quinacridone compared with pentacene during redox reactions

“…3 However, differences in the charge carrier concentration were found. 18 Further, these compounds have been oxidized by using iodine as an oxidation agent and spectroscopic changes have been elucidated in the UV-VIS up to mid-IR range, including electron paramagnetic resonance (EPR) and conductivity measurements. 18 While pentacene shows the formation of radical cations, which are transformed to a spinless species in a higher oxidation state, quinacridone shows only the formation of radical cations.…”

“…18 Further, these compounds have been oxidized by using iodine as an oxidation agent and spectroscopic changes have been elucidated in the UV-VIS up to mid-IR range, including electron paramagnetic resonance (EPR) and conductivity measurements. 18 While pentacene shows the formation of radical cations, which are transformed to a spinless species in a higher oxidation state, quinacridone shows only the formation of radical cations. In addition, this spectroscopic study has been connected to device performance to explain the enhanced chemical stability of the semiconductor quinacridone, which for example has not been achieved for pentacene.…”

“…2 Density functional theory (DFT) calculations addressing the enhanced chemical stability issue for quinacridone have also been reported in the literature. 18 Herein, we discuss a technique which is an extension of the mentioned results, where spectroscopic changes of both compounds are considered by using electrochemical methods. The main advantages of spectroelectrochemistry are that reduction reactions can be performed more easily, the redox levels can be controlled by applying a certain potential as well as higher oxidized species can be analyzed, which may be difficult to achieve upon chemical oxidation reactions.…”