Room-temperature phosphorescence of 3- and 5-substituted indoles

The room-temperature phosphorescence of indole and thirteen substituted indoles on Schleicher and Schüll 2040A filter paper is reported. Caesium and iodide ions are effective in increasing the emission intensity. In the presence of iodide, the excitation and emission wavelengths of indole are 279 and 440 nm respectively. The excitation and emission wavelengths of indoles with aliphatic groups in the 3-position are 288-289 and 443-449 nm respectively. Indoles with 3,5-substitution have excitation and emission wavelengths of 300-308 and 448-460 nm respectively. Indoxylsulphate and indoxyl-beta-d-glucoside were the only indoles surveyed for which variations in the excitation and emission wavelengths depended on the heavy-atom ion present. These compounds had excitation wavelengths ranging from 288 to 388 nm, depending on which heavy-atom perturber was used. Emission wavelengths were 460-500 nm. Log-log plots of intensity vs. concentration were linear between 0.05 and 700 microg/ml for all the compounds studied, with detection limits in the nanogram range.