Gas-phase preparation of the dibenzo[e,l]pyrene (C24H14) butterfly molecule via a phenyl radical-mediated ring annulation

Abstract

A high temperature phenyl-mediated addition–cyclization–dehydrogenation mechanism to form peri-fused polycyclic aromatic hydrocarbon (PAH) derivatives—illustrated through the formation of dibenzo[e,l]pyrene (C₂₄H₁₄)—is explored through a gas-phase reaction of the phenyl radical (C₆H₅˙) with triphenylene (C₁₈H₁₂) utilizing photoelectron photoion coincidence spectroscopy (PEPICO) combined with electronic structure calculations. Low-lying vibrational modes of dibenzo[e,l]pyrene exhibit out-of-plane bending and are easily populated in high temperature environments such as combustion flames and circumstellar envelopes of carbon stars, thus stressing dibenzo[e,l]pyrene as a strong target for far-IR astronomical surveys.