Lifetime of the Pyrene Dimer

Abstract

THE appearance of a new fluorescence emission band in concentrated solutions of pyrene was attributed by Förster and Kasper¹ to an excited dimer formed by combination of. an excited singlet molecule with an unexcited molecule. Stevens and Hutton² have recently reported the lifetime of the dimer emission to be 1.8 × 10⁻³ sec. During tests of a new photoelectric spectrophosphorimeter an attempt was made to record this long-lived emission. The instrument was a modification of a spectrofluorimeter previously described³, but in which two 800 c./s. choppers were used, one being situated in tfce beam of the exciting light and one in the beam of the fluorescence light. The choppers were driven by synchronous motors, and by rotation of one of the motors the choppers could be put into or out of phase so that the fluorescence monochromator could be made to record either the sum of the fluorescence and phosphorescence spectra or the phosphorescence spectrum alone. By adjustment of the photomultiplier voltage and by variation of the amplifier gain, the overall sensitivity could be increased by a factor of 10⁴.