Ultrafast relaxation dynamics of the photoexcited one-dimensional molecular chain coupled with the phonon field is theoretically investigated. The time evolution of the system is formulated by the time-dependent variational method with a coherent state trial function. The temporal changes of the exciton coherence size and the energy relaxation strongly depend on the exciton transfer, the exciton-phonon coupling strength, and the phonon bandwidth. The calculated time-resolved spontaneous emission spectrum well reflects the temporal change of the exciton coherence: The intensity and the peak position represent the coherence size and the energy dissipation. A cooperative spontaneous emission, super-radiance, periodically appears as long as the exciton coherence maintains over the entire system as a result of in-phase oscillation of phonon modes. (C) 2003 American Institute of Physics.