Gas-phase preparation of the dibenzo[ e,l ]pyrene (C 24 H 14 ) butterfly molecule via a phenyl radical-mediated ring annulation.

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 (C 24 H 14 )-is explored through a gas-phase reaction of the phenyl radical (C 6 H 5 ˙) with triphenylene (C 18 H 12 ) 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.