Room temperature luminescence of 5-chloroindole

Abstract

• Luminescence of 5-chloroindole in poly(vinyl alcohol) at room temperature. • High phosphorescence anisotropy using a longer wavelength of excitation. • Direct excitation to the triplet state of 5-chloroindole. • Phosphorescence lifetime using direct excitation of 5-chloroindole. • Temperature sensitivity of both fluorescence/phosphorescence of 5-chloroindole. This work studied 5-chloroindole room temperature fluorescence/phosphorescence when embedded in poly (vinyl alcohol) (PVA) films. The fluorescence emission of 5-chloroindole is strongly quenched compared to indole. In contrast, the phosphorescence of 5-chloroindole is twice stronger than indole, which points to an increased intersystem crossing rate. We also found that not only UV light excites 5-chloroindole to the triplet state, but much longer wavelengths of excitation (in the blue region) can effectively populate the triplet state of 5-chloroindole and result in phosphorescence emission. Room temperature phosphorescence of 5-chloroindole with UV excitation has low/negative anisotropy. However, with long-wavelength excitation (directly to the triplet state), the anisotropy of phosphorescence is high. We believe that the long-wavelength direct triplet state excitation offers new possibilities for triplet state spectroscopy.