Phosphorescence of Adsorbed Trypaflavine and Its Quenching by Oxygen

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Abstract
Dyes adsorbed at, or imbedded in, solids have a greater yield of fluorescence and phosphorescence than they do in liquid solutions. As an hypothesis, it is suggested that hindrance of the natural movement of the atoms in the dye molecule causes a delay in the internal conversion of excitation energy into molecular oscillation energy, thus favoring the re‐emission of light. The green phosphorescence of trypaflavine adsorbed on silica gel, is half quenched by oxygen at 5×10−5 mm pressure; the quenching at higher oxygen pressures is much smaller than would be expected. This fact indicates that two long‐lived excitation states (tautomers of trypaflavine) share in causing the green phosphorescence. The first (M1) is very sensitive to oxygen, whereas the second (M2) is insensitive. The phosphorescence still visible at the higher oxygen pressures owes its origin entirely to M2. The quenching in this pressure range is due to the oxygen sensitivity of F, the unstable state responsible for the green fluorescence. Water vapor does not quench the phosphorescence. The quenching described by Kautsky is due to oxygen liberated from the gel by a process in which strongly adsorbed oxygen molecules are dislodged by water molecules.