Acid-Mediated Dimerization of TIPS-Pentacene

TIPS-pentacene (<b>TIPS-Pc</b>), a benchmark organic semiconductor, is shown to undergo acid-induced dimerization upon treatment with strong Bro̷nsted acids, such as trifluoroacetic acid (TFA). Mechanistic studies indicate that some acids oxidize the pentacene core to form a radical cation, which then engages a second neutral <b>TIPS-Pc</b> molecule in a radical-mediated [4 + 2] cycloaddition. Subsequent neutralization with triethylamine furnished isolated dimer <b>1</b>. Spectroscopic analysis, isotopic test, and DFT calculations converge on this pathway, revealing acid-triggered, radical-cation-driven dimerization as an unrecognized degradation mode of <b>TIPS-Pc</b>.