Makoto Tadokoro of the Tokyo University of Science and colleagues report the synthesis of a new organic material with potential as an n-type semiconductor. Writing in the journal Organic and Biomolecular Chemistry, the team explains that "organic semiconductor devices, unlike hard inorganic semiconductor devices, are very soft and are useful for creating adhesive portable devices that can easily fit on a person." They point out that while stable, inorganic n-type semiconductors are well known their organic counterparts are yet to fully emerge.
The team has as its starting point N-heteroheptacenequinone, which is a well-known candidate for an organic n-type semiconductor materials. Unfortunately, this substance is unstable in air and degrades under ultraviolet-visible light, moreover it is insoluble in organic solvents. Such obstacles have so far limited its development for practical applications. The team hoped to work around these issues and have produced a derivative dubbed C6OAHCQ using a four-step process to generate what turns out to be a red solid product. The substance has a unique crystalline near-planar structure containing two tetraazanaphthacene backbones and a single benzoquinone backbone. Most critically, it has eight electron-deficient imino-N atoms and two carbonyl moieties.
The team carried out various tests on the material including the recording of its UV-Vis absorption spectrum in solution as well as cyclic voltammetry, and theoretical calculation of the compound's electrostatic potential. They compared the results with a tetraazapentacenequinone analog. [Isoda, K. et al., Org. Biomol. Chem. (2019); DOI: 10.1039/C9OB01323G]
The novel compound has several unique properties due to the electron-deficient imino-N atoms and the two carbonyl moieties which endow it with electron-accepting behavior. Indeed, the number of electrons that can be accepted by the new compound is more than that accepted by the 60-carbon compound, buckminsterfullerene which the team suggests hints at better conductivity. The cyclic voltammetric data showed that it exhibits reversible four-step, four-electron reduction waves, meaning it is not only stable but has good electrostatic potential. The fact that UV-Vis spectroscopy was possible also proves its photostability.
The material has electrochromic characteristics, which might one day make it useful in certain specialized semiconductor areas, smart windows, electrochromic mirrors, and electrochromic display devices, perhaps.
Tadokoro and his team write that "the identification of this organic acceptor molecular skeleton that has the property of stably receiving electrons is very important, as it can be used to develop molecular devices with new functionality."
David Bradley blogs at Sciencebase Science Blog and tweets @sciencebase. His popular science book Deceived Wisdom is now available.