The phosphorescence of phenanthrene, pyrene, and naphthalene in fluid solutions has been studied. The radiative lifetimes are calculated from the quantum yields and actual lifetimes and vary only slightly or not at all with temperature within the experimental error. For phenanthrene, pyrene, naphthalene, and anthracene the radiative lifetimes at 77°K in ethanol are 25, 30, 75, and 180 sec, respectively. The temperature dependence and the absolute value of the triplet–triplet annihilation efficiency vary from molecule to molecule. The results are discussed in terms of a re-encounter association of the annihilation partners to form an excimer.

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