One- and two-photon singlet oxygen generation with new fluorene-based photosensitizers

The, spectral properties of new fluorene-based photosensitizers for efficient singlet oxygen production are investigated at room temperature and 77 K. Two-photon absorption (2PA) cross-sections of the fluorene derivatives are measured by the open aperture Z-scan method. The quantum yields of singlet oxygen generation under one- and two-photon excitation (Phi(Delta) and (2PA)Phi(Delta,) respectively), are determined by the direct measurement of singlet oxygen luminescence at approximate to 1270 nm. The values of Phi(Delta) are independent of excitation wavelength, ranging from 0.6-0.9. The singlet oxygen quantum yields under two-photon excitation are (2PA)Phi(Delta) approximate to 1/2 Phi(Delta), indicating that the two processes exhibit the some mechanism of singlet oxygen production, independent of the mechanism of photon absorption.