Fig. 2
From: Plasmonic photocatalyst-like fluorescent proteins for generating reactive oxygen species
Jablonski diagram of photosensitizer and molecular oxygen (O2). a Photosensitization with the singlet ground (S0) and excited (S *1 ) states and their further interactions with O2. The triplet excited state (T *1 ) through an intersystem crossing (ISC) process can undergo electron (e−) transfer to the ground state of molecular oxygen O2(3Σ −g ) (i.e. 3O2), generating superoxide anion (O •‒2 ) and other ROS products (e.g. H2O2 and –OH•) as Type I photoreaction. In addition, T *1 can undergo energy (E) transfer to 3O2, producing highly cytotoxic O2(1Δg), commonly known as singlet oxygen (1O2), as Type II photoreaction. b Electronic configuration of the triplet ground state molecular oxygen O2(3Σ −g ), its first (i.e. lowest-energy) singlet excited state O2(1Δg), and its second (higher energy) singlet excited state O2(1Σ +g ) [36, 37], where the superscripts 3 and 1 indicate triplet and singlet states, respectively. The energy gaps between the ground state and the two singlet excited states are shown in eV, including the corresponding luminescent wavelengths