Some photophysical properties of electronically excited phenyldibenzophosphole in rigid polymer matrices

Phenyldibenzsphosphole (PDP), present as a dopant in polymer matrices, has been subjected to photoexcitation by 308 nm excimer laser pulses. Both polystyrene (PS) and poly(butyl methacrylate) (PBuMA) have been used as hosts. Luminescence spectra and transient absorption spectra and their respective temporal behavior have been recorded for samples varying in PDP content from 2 to 15% by weight. The time regime from several tens of nanoseconds to seconds was investigated. Phosphorescence decays examined at 15 K yield a lifetime component in the microsecond domain as well as a very long-lived component on the order of seconds. In addition to the phosphorescence spectrum, with origin at 427 nm, a shorter wavelength component with origin near 350 nm is found. In polymer hosts a band at 395 nm is also observed. This latter is assigned to delayed excimer fluorescence while the 350 nm component is delayed monomeric fluorescence. Similarly, an emission at 500 nm is found which grows relative to the main phosphorescence peak at 470 nm with increasing solute concentration. This band is assigned to an excited state van der Waals complex. Transient triplet absorption decays were very well represented by a rate equation for concurrent first- and second-order kinetics. Similar first-order rate constants were found both in PS and PBuMA. The second-order component is believed to be due to triplet-triplet annihilation. Phosphorescence decays yield first-order rate constants in excellent agreement with those obtained by transient absorption. All aspects of the photophysics are strongly influenced by the dramatic non-homogeneity of the solute distribution.