Triplet state dynamics in poly(2,5-pyridine diyl)

Pulse radiolysis was used to determine the triplet state energy (2.3 eV) of Poly(2,5-pyridine diyl) (PPY) film which was found to be coincident with t he emission energy. Derailed time-resolved photoluminescence (PL) and pump- probe measurements have been applied to study the photoexcited state relaxa tion dynamics. In films, a very large spectral red-shift (similar to0.35 eV ) for the PL occurred within the first 100 ps whereas no spectral red-shift was observed for the PPY in solution. This result shows clear evidence for the evolution of short-lived singlet emission (S-1 --> S-0) at similar to 450 nm to long-lived tripler emission (T-1 --> S-0) at similar to 520 nm fo r the PPY thin film. Streak camera measurement indicates the long live comp onent has a decay time constant of several ns. The picosecond photo-induced triplet state absorption (T-1 --> T-2 transition) peaks at similar to 600 nm as measured by pump-probe which is consistent with both the radiolysis a nd cw photoinduced absorption measurements. A triplet lifetime of similar t o6 ns is measured which is again consistent with the streak camera measurem ent. These results lead us to believe that the long live component of the e mission from PPY film is in fact phosphorescence. Furthermore, there is evi dence that oxygen plays a very important role in the fast tripler radiative lifetime in PPY films. (C) 2001 Elsevier Science B.V. All rights reserved.