Photoluminescence in pyridine-based polymers: role of aggregates.

The morphol. dependence of the photoluminescence (PL) properties of the pyridine-based polymers, poly(p-pyridylvinylene), poly(p-pyridine), and poly(p-pyridylvinylene-p-phenylenevinylene) (PPyVPV) was studied. The photoluminescence of soln. samples is characterized by high quantum efficiency (>70% in PPyVPV), weak coupling to vibrational modes (Huang-Rhys parameter ∼0.5) and a single-exponential decay (radiative lifetime ∼1 ns). On the other hand, film samples display strongly red shifted, featureless emission with low quantum yield (<20%) and highly nonexponential decay dynamics. Through consideration of absorption and excitation spectra, the "site-selectivity" of the PL, and the concn. dependence of the PL spectrum, we demonstrate that the red shifted film spectra are a result of the formation of low-energy aggregate sites due to strong interchain interactions. Time-resolved measurements suggest a longer radiative lifetime for the aggregate vs. soln., leading to the lower efficiency. Aggregate formation is morphol. dependent, and is minimal in "powder" samples which are pptd. after polymn. [on SciFinder(R)]