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We present a study of the morphology dependence of the photoluminescence (PL) properties of the pyridine-based polymers poly (p-pyridyl vinylene), poly (p-pyridine), and poly (p-pyridyl vinylene p-phenylene vinylene) (PPyVPV). The photoluminescence of solution 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 redshifted, 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 concentration dependence of the PL spectrum, we demonstrate that the redshifted 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 solution, leading to the lower efficiency. Aggregate formation is found to be morphology dependent, and is minimal in ``powder'' samples which are precipitated after polymerization. 1996 The American Physical Society.
Blatchford et al. (1996) studied this question.