Singlet molecular oxygen: Early history of spectroscopic and photochemical studies with contributions of A.N. Terenin and Terenin's school

This paper is based on the lecture delivered by the author at the memorial meeting dedicated to the 120th birthday of A.N. Terenin. The paper starts from the historical account devoted to the initial steps in the development of singlet oxygen photonics from Fraunhofer to Egoroff, Janssen, Olszewski, Mulliken and Kautsky. Principal contributions of AN. Terenin to this field are briefly discussed in parallel with major results of his contemporaries. The discussion deals with pioneering Terenin's papers on the triplet nature of the dye phosphorescent state, involvement of singlet and triplet dye molecules in photooxygenation reactions, dye-sensitized generation of singlet oxygen, interpretation of Kautsky's experiments in heterogeneous systems and classification of photosensitized oxygenation reactions. The initial projects of the author of the present paper dealing with singlet-oxygen mediated photochemiluminescence of dyes and the first papers dealing with the photosensitized phosphorescence of singlet oxygen in the solution phase are briefly summarized.