Tweaking the Optoelectronic Properties of S-Doped Polycyclic Aromatic Hydrocarbons by Chemical Oxidation

Peri-thiaxanthenothiaxanthene, an S-doped analog of peri-xanthenoxanthene, is used as a polycyclic aromatic hydrocarbon (PAH) scaffold to tune the molecular semiconductor properties by editing the oxidation state of the S-atoms. Chemical oxidation of peri-thiaxanthenothiaxanthene with H2O2 led to the relevant sulfoxide and sulfone congeners, whereas electrooxidation gave access to sulfonium-type derivatives forming crystalline mixed valence (MV) complexes. These complexes depicted peculiar molecular and solid-state arrangements with face-to-face pi-pi stacking organization. Photophysical studies showed a widening of the optical bandgap upon progressive oxidation of the S-atoms, with the bis-sulfone derivative displaying the largest value (E-00=2.99 eV). While peri-thiaxanthenothiaxanthene showed reversible oxidation properties, the sulfoxide and sulfone derivatives mainly showed reductive events, corroborating their n-type properties. Electric measurements of single crystals of the MV complexes exhibited a semiconducting behavior with a remarkably high conductivity at room temperature (10(-1)-10(-2) S cm(-1) and 10(-2)-10(-3) S cm(-1) for the O and S derivatives, respectively), one of the highest reported so far. Finally, the electroluminescence properties of the complexes were tested in light-emitting electrochemical cells (LECs), obtaining the first S-doped mid-emitting PAH-based LECs.

Automated summary

Peri-thiaxanthenothiaxanthene is a sulfur-doped derivative of peri-xanthenoxanthene, which can be used to manipulate the properties of semiconductor materials by adjusting the oxidation state of the sulfur atoms. Chemical and electrochemical oxidation of peri-thiaxanthenothiaxanthene resulted in the formation of sulfoxide, sulfone, and sulfonium derivatives. These derivatives exhibited unique molecular and solid-state arrangements, with face-to-face pi-pi stacking organization. The optical bandgap of the compounds increased as the sulfur atoms were progressively oxidized, with the bis-sulfone derivative displaying the widest bandgap. The MV complexes showed high conductivity at room temperature, making them promising for semiconductor applications. Additionally, the electroluminescence properties of the complexes were tested, and they were found to be the first sulfur-doped mid-emitting PAH-based light-emitting electrochemical cells.