Singlet oxygen generation by two-photon excitation of porphyrin derivatives having two-photon-absorbing benzothiadiazole chromophores

Porphyrin derivatives with four two-photon absorbing 2,1,3-benzothiadiazole chromophores at the meso positions provide large two-photon absorption cross-sections up to 735 GM as well as large quantum yields of one-photon singlet oxygen sensitization of ca. 0.7, leading to generation of singlet oxygen by two-photon excitation of 800 nm. The two-photon singlet oxygen sensitization is discussed on the basis of a parameter of the normalized oxygen luminescence intensity obtained from the two-photon experiment.