FLUORESCENCE CHARACTERISTICS OF INDOLES IN NON‐POLAR SOLVENTS: LIFETIMES, QUANTUM YIELDS AND POLARIZATION SPECTRA

Abstract
Abstract— Fluorescence lifetimes, quantum yields and polarization spectra were measured for indole, 3‐methylindole and 2,3‐dimethylindole in non‐polar solvents. The results indicate simultaneous emission from thermally equilibrated 1La and 1Lb levels, with 1La1A dominating the 2,3‐dimethylindole emission, and 1Lb1A dominating the indole emission. These results are consistent with previous assignments of the 0‐0 transitions in absorption for these compounds. Radiative rates are: 1La1A, 2·0 × 108 S‐1 and 1Lb1A. 0·62 → 108 S‐1. In addition, the temperature dependence of the excitation and emission spectra are presented, which show that aggregation occurs with these indoles in hydrocarbons below approximately ‐ 110°C. Possible applications to tryptophyl emission in the hydrophobic interiors of proteins are briefly discussed.