The photon emission statistics from a single molecule containing multichromophores under pulsed excitation is theoretically studied. Fast nonradiative pair annihilation of excitons efficiently produces a single exciton, which acts as a single photon emitter. By taking into account the discrete nature of exciton numbers and the competition among pair annihilation, and unimolecular radiative and nonradiative decay of excitons, we obtain analytical expressions of photon emission statistics, the average number of emitted photons, and the normalized photon pair correlation which represents the ratio of the number of photon pairs created by the same pulse to that created by different pulses. The normalized photon pair correlation is influenced by the ratio of the pair annihilation rate to the total unimolecular decay rate including both radiative and nonradiative processes but is not influenced by the ratio of the unimolecular radiative and nonradiative rates. On the other hand, the single photon emission intensity depends on the ratio of the unimolecular radiative and nonradiative rates from the exciton left alone after pair annihilation. The conclusion is consistent with recent experimental results on conjugated polymers with various sizes in different host materials.