Spectroscopic signatures of protonated perylene in concentrated sulfuric acid

Protonated perylene is an important intermediate in the oxidation of perylene to its radical cation in oxidizing environments, and has been implicated in recent investigations of photoinitiated reaction kinetics in nonpolar solvents. The literature on its spectral signatures in concentrated sulfuric acid provides a well-characterized absorbance spectrum, but its emission characteristics remain ambiguous. In this paper we present the absorbance and emission spectrum of protonated perylene in concentrated sulfuric acid. We demonstrate that dissolution of perylene in concentrated sulfuric acid occurs through the protonated perylene intermediate, which is completely oxidized to the radical cation in the air-saturated liquid within 1 h after dissolution of solid perylene. During this time it is possible to selectively excite protonated perylene in the presence of other absorbing species, and we use this fact to measure the emission spectrum of protonated perylene in concentrated sulfuric acid. Protonated perylene’s emission spectrum has a peak at 670 nm. The fluorescence decay of this species exhibits single-exponential behavior when excited at 625 nm, which demonstrates that a single emissive species is prepared.