Photophysical properties of a series of polyisocyanides possessing porphyrin pendants (porphyrin polymers) were investigated by steady state and transient spectroscopic methods. The B (Soret)-band of the free base porphyrin polymers showed splitting indicating substantial exciton coupling in the porphyrin polymers due to a face-to-face stacking conformation. On the other hand, the B-band of the zinc porphyrin polymers split into four peaks indicating deviation from the strict face-to-face stacking conformation. The fluorescence quantum yields of the porphyrin polymers were small compared with those of the corresponding monomers and dimers. Furthermore, the fluorescence decay profiles of the porphyrin polymers deviated from single-exponential decay due to the structural heterogeneity of the polymers. It was revealed that the porphyrin polymers showed transient absorption changes attributable to the exciton-exciton annihilation accompanying structural change with the rate constant of (2-4) x 10(10) s(-1) regardless of the length of the polymer chain. The quantum yields of the intersystem crossing of the polymers were smaller than those of monomers due to the efficient exciton-exciton annihilation process in the singlet excited states. In the block copolymers of zinc and free base porphyrins, energy transfer processes from zinc to free base porphyrin moieties were confirmed by time-resolved fluorescence spectral and transient absorption spectral measurements. It became clear that the energy transfer rates were almost independent of the sequence of the block copolymers, suggesting that the rate-determining step of the energy transfer in the present block copolymers is the process at the interface of zinc and free base porphyrins because of the sufficiently fast exciton migration in each block.