Absorption and luminescence of pyridine-based polymers

We summarize the low energy photophysics of the pyridine-based polymers poly(p-pyridine)(PPy), poly(p-pyridyl vinylene) (PPyV) and copolymers made up of PPyV and poly(p-pheneylene vinylene) (PPyVPV). The absorption and luminescence properties are morphology dependent. The primary photoexcitations within these polymers are singlet excitons which may emit from individual chains following a random walk to lower energy segments, depending upon the excitation energy. Films display redshifted absorption and emission properties with a decrease in photoluminescence efficiency which can be attributed to aggregate formation in comparison to powder and solution forms. Photoinduced absorption (PA) studies show direct conversion of singlet to triplet excitons on the ps time scale. Polaron signatures and the transition between triplet exciton states are seen in powder forms using ms PA techniques. Film forms display only a polaron signature at millisecond times indicating that morphology plays a key role in the long-time photophysics for these systems. Photoluminescence detected magnetic resonance studies also have signatures due to both polarons and triplet excitons. The size of the triplet exciton is limited to a single ring suggesting that the triplet exciton may be trapped by extrinsic effects.