Fluorescence quenching has been observed in 10minus;4to 10minus;7Msolutions of metalhyphen;free phthalocyanine in 1hyphen;chloronaphthalene at 77deg;K. This quenching is attributed to singletndash;triplet fusion. A triplet lifetime of 200 mgr;sec was measured at 77deg;K. A dipolendash;dipole interaction formulation for singlet excitation migration was adapted to the singletndash;triplet fusion process. A critical distance of about 200 Aring; was computed for the system under study. Unlike in singlet excitation migration, this critical distance depends on the experimental illumination conditions. If singletndash;triplet fusion plays a role in photogeneration of charge carriers in metalhyphen;free phthalocyanine thin films, a photocurrent linear in light intensity, in the absence of recombination and trapping effects, can be understood.
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