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.