Spectroscopy and Reactivity of Dialkoxy Acenes

• Published in: Chemistry : a European journal 2019-08, Vol.25 (44), p.10400-10407
• Main Authors: Brega, Valentina, Kanari, Sare Nur, Doherty, Connor T., Che, Dante, Sharber, Seth A., Thomas, Samuel W.
• Format: Article
• Language: English
• Subjects: acenes; Acidic oxides; Alkylation; Aromatic compounds; Chemistry; Cores; Density functional theory; Drug delivery; Drug delivery systems; endoperoxide; fluorescence; Functional materials; Irradiation; NMR; Nuclear magnetic resonance; Optoelectronics; Organic chemistry; organic synthesis; Oxidation; Photochemicals; Quinones; Radiation; Reactive oxygen species; Reductive alkylation; Singlet oxygen; Spectroscopy; Time dependence
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201901258

Photochemical oxidation of acenes can benefit or impede their function, depending on the application. Although acenes with alkoxy substituents on reactive sites are important for applications as diverse as drug delivery and organic optoelectronics, the influence of chemical structure on their photochemical oxidation remains unknown. This paper therefore describes the synthesis, spectroscopic properties, and reactivity with singlet oxygen (1O2) of a series of dialkoxyacenes that vary in the number and types of fused rings in the (hetero)acene cores. Reductive alkylation of quinone precursors yielded target dialkoxyacenes with fused backbones ranging from benzodithiophene to tetracenothiophene. Trends of their experimental spectroscopic characteristics were consistent with time‐dependent density functional theory (TD‐DFT) calculations. NMR studies show that photochemically generated 1O2 oxidizes all but one of these acenes to the corresponding endoperoxides in organic solvent. The rates of these oxidations correlate with the number and types of fused arenes, with longer dialkoxyacenes generally oxidizing faster than shorter derivatives. Finally, irradiation of these acenes in acidic, oxidizing environments cleaves the ether bonds. This work impacts those working in organic optoelectronics, as well as those interested in harnessing photogenerated reactive oxygen species in functional materials. Dialkoxyacenes with three or more fused rings react rapidly with singlet oxygen (1O2) to yield endoperoxides, with potential applications in 1O2 detection or degradable materials.