Triplet energy transfer in solid solutions and films of poly(vinyl carbazole)

Abstract

AbstractMonomeric carbazole derivatives show phosphorescence in the wavelength region between 400 and 500 nm. Poly(vinyl carbazole) (PVCA) in dilute frozen solutions also shows phosphorescence in this region and, in addition, delayed fluorescence owing to triplet‐triplet annihilation. The latter depends on the molecular weight of the polymer, high‐molecular weight samples showing very strong delayed fluorescence, whereas in low‐molecular weight products phosphorescence prevails.The phosphorescence of solid PVCA is governed by traps. Comparison with low‐temperature fluorescence and measurement of decay times suggest that two traps are important for both singlet and triplet excitons. The excimer‐forming site is one of them. The maximum of triplet excimer emission is at about 500 nm, the decay time is 7.9 ± 1 sec (compared to 410 nm and 43 nsec in the singlet system). The second trap emits in the same wavelength region, decay time 1.4 sec, and corresponds to a second intrinsic singlet trap emitting at 380 nm (decay time 12 nsec). The range of the triplet exciton at 77°K is drastically reduced by these traps, as in the case of the singlet system.