Abstract

The charge carriers in p-type organic semiconductors are holes, which commonly correspond to π-conjugated radical cations.[1] As a result, the operation of various organic electronic devices depends on controlling formation of π-conjugated radical cations. For example, radical cations are formed in a p-type organic field transistor (OFET) as induced by a gate voltage to result in the conduction channel; and radical cations are formed in p-type semiconductors in an organic solar cell as a result of photo-induced charge separation. π-conjugated radical cations are typically reactive species that are difficult to isolate.[2] 

Herein we report unusually stable π-conjugated radical cations resulting from oxidation of hexabenzoperylene (HBP) derivatives, HBP-B and HBP-H (Figure a), which lack an embedded 7π heterocycle/carbocycle or bulky protecting substituents. The radical cation of HBP-B was successfully crystallized in the form of hexafluorophosphate, which exhibited conductivity as high as 1.32 ± 0.04 S cm−1 (Figure c). Photochemical oxidation of HBP-H by molecular oxygen led to formation of its radical cation in the solid state as found with different techniques (Figure d). This allowed the organic field effect transistor of HBP-H to function as a nonvolatile optoelectronic memory with a memory switching contrast above 103 and long-term stability without using a floating gate, an electret layer, or photochromic molecules. 

References

1 Y. Shirota, H. Kageyama, Chem. Rev. 2007, 107, 953-1010.

2 T. Harimoto, Y. Ishigaki, ChemPlusChem 2022, e202200013.