Tetrabenzo[a,f,j,o]perylene: a polycyclic aromatic hydrocarbon with an open-shell singlet biradical ground state.

A novel tetrabenzo[a,f,j,o]perylene, namely "bistetracene" in which two tetracenes are connected side by side with two bonds, was synthesized and characterized. An optical energy gap of about 1.56 eV is derived from the UV/Vis absorption spectrum, showing the low optical gap feature of such zigzag-edged polycyclic aromatic hydrocarbons (PAHs). Theoretical calculations and physical property investigations manifest that such a PAH possesses a prominent biradical character in the ground state, which is the first example among bistetracene derivatives. However, the bistetracene can easily undergo oxidation to tetrabenzo[a,f,j,o]perylene-9,19-dione (diketone) under ambient conditions. Thereby, such zigzag-edged PAH provides insight into understanding the edge state of other expanded homologues, such as peri-tetracenes or peri-pentacenes.