Fluorescence Quenching in Aromatic Hydrocarbons by Oxygen

The role of the possible fluorescence quenching process S1 + O2(1Σg−) → T + O2(1Δg) which involves energy transfer to oxygen is examined in a number of aromatic hydrocarbons. It is observed that quenching is just as efficient in aromatics where the S1–T energy gap is too small (< 7900 cm−1) for excitation of oxygen in the above process as in aromatics where it is allowed energetically. This process cannot therefore account for the general phenomenon of fluorescence quenching by oxygen in aromatics. Evidence bearing on other quenching mechanisms is discussed.