Purification and Decay Time of Delayed Fluorescence of Chrysene Crystal

Abstract

Chrysene crystal was extensively purified. The decay time of delayed fluorescence was measured with the purified crystal and the triplet exciton lifetime at room temperature was found to be 50 ms.

In a molecular crystal, impurities and defects cause various sorts of traps in the triplet exciton level. As the population at the triplet state decreases effectively through the traps, these traps reduce the triplet lifetime.¹ Benz² has observed that the triplet lifetime of naphthalene increases with the number of zone passes upon zone purification. Further, Port et al.³ have shown that the triplet lifetime of naphthalene crystal decreases with an increase of the concentration of anthracene impurity. The triplet lifetime of anthracene crystals has also been examined in relation to purity.^4,5 Thus, in general, the triplet lifetime may be expected to serve as an index of the purity of molecular crystals, particularly in the very low concentration range, where there are no analytical methods to determine the purity. In this connection few data about chrysene crystals have been reported.⁶ In this work the triplet lifetime of an extensively purified chrysene crystal was measured at room temperature. Since the chrysene crystal gave no phosphorescence, the decay of its delayed fluorescence was measured. Details about the delayed fluorescence spectra obtained will be reported elsewhere.