TRIPLET PHOTOPHYSICAL PROPERTIES OF POLY[[4-(N,N-DIPHENYLAMINO)PHENYL]METHYL METHACRYLATE]

The triplet-state properties of the subject polymer, poly[[4-(N,N-diphenylamino)phenyl]-methyl methacrylate ] (PDAPM), have been examined in rigid solutions from 77 to 298 K. Solid films of the polymer have been studied in the temperature range from 8 K to ambient. In rigid solutions the triplet emission spectrum consists of a delayed fluorescence band and a phosphorescence band with its origin at 420 nm. In solid films at 8 K, the origin of the phosphorescence band is found at 426 nm and the spectrum is nonexcimeric in character. This nonexcimeric phosphorescence spectrum is gradually replaced by a band at 485 nm with rising temperature from 8 to near 60 K. The 485-nm band is thought to be an excimerlike phosphorescence. Its formation requires an activation energy of 5.1 +/- 0.5 kJ/mol. The activation energy found for excimer dissociation implies that the triplet excimer and the nonexcimer triplets in the solid state are nearly isoenergetic. An additional band at 560 nm is found in spectra of solid films and rigid solutions from 8 K to ambient and is also found in concentrated solutions of the monomeric model compound. The species emitting at 560 nm is most likely formed by sensitization, and its supralinear dependence upon excitation intensity suggests it is sentized by mobile triplet excitons. The delayed fluorescence (DF) intensity depends upon the square of the excitation intensity and evidently arises by an annihilative mechanism.