The photophysical properties of poly(2,5-pyridine diyl) (PPY) are characterized in detail using steady state measurements, time correlated single photon counting techniques, and excitation pulse energy dependence of the photoluminescence intensity. Our results show that the blue emission from dilute solution is prompt fluorescence (lifetime similar to10 ps). On the other hand, the green emission from thin solid film consists of phosphorescence as well as delayed fluorescence with lifetimes of similar to4.8 ns and 1.1 ns, respectively. Oxygen complexation plays an important role and increases triplet population in thin film. At low excitation pulse energies, emission in thin film originates mostly from the triplet state, while at higher excitation pulse energies, delayed fluorescence becomes the major part in the emission. Also, at low temperature (20 K), an excimerlike emission is observed to the red side of the PPY emission spectrum in thin film, which is only induced by pressure.