Photooxidation and Cleavage of Ethynylated 9,10-Dimethoxyanthracenes with Acid-Labile Ether Bonds

This paper describes a series of 12 9,10-dimethoxyanthracene derivatives functionalized with a range of electronically diverse ethynyl substituents at the 2 and 6 positions, aimed at tuning their optoelectronic properties and reactivity with singlet oxygen (¹O₂). Optical spectroscopy, cyclic voltammetry, and density functional theory calculations reveal that the ethynyl groups decrease the HOMO-LUMO gaps in these acenes. Notably, bis(dimethylanilineethynyl) substituents increase the wavelength of absorbance onset by over 60 nm compared to 9,10-dimethoxyanthracene (DMA). Furthermore, all 12 molecules react with ¹O₂ through cycloaddition at the 9 and 10 positions to form endoperoxides. Although the presence of ethynyl groups decreases the reaction rates, they are at least 40% of the rate observed for DMA. Finally, these endoperoxides cleave to form quinones when exposed to protic acid. This behavior, combined with the red-shifting of absorbance spectra, emphasizes their potential in photocleavable materials.