The population dynamics and associated coherent oscillations have been studied by the three-and four-state models of pentacene and tetracene dimer. The role of the CT state can be directly measured by the relative magnitude of population of CT states. In pentacene model, we observed that the magnitude of the CT state is limited to the value of 0.1 and rapidly decay to zero within 500 fs. The PSF process in pentacene is known to occur in 100 fs. It implies that the impact of the CT state is curtailed by the ultrafast population transfer in pentacene crystal. Moreover, the vibronic interactions of inter/intramoelcular vibrations degenerate the PESs and form the conical intersections between electronic singlet and triplet-pair states, which even drives the ultrafast deactivation of PSF. This mechanism even further weaken the role of CT states in pentacene crystal. It is known that the coherent vibrations observed previously in the experiments allows the formation of conical intersection with multi-dimensions, which form the effective channel for the deactivation and speed up the population transfer from the singlet states to triplet-pair state. In contrast, the CT state plays more important role in the SF process of tetraceme dimer model. Firstly, the magnitude of CT state shows a relatively larger amplitude as compared to the TT state. Secondly, the relatively longer timescle of transfer in tetracene molecules enhance the importance of CT state, which is parallel to the channel of conical intersection between the singlet and triplet-pair states. Additionally, the calculations of tetracene, the coherent dynamics and the associated lifetimes also show the significant differences between the three-state and four-state models. The four-state model of tetracene presents a very complicated coherent dynamics of intra/intermolecular modes along with the observed frequency-shifts of vibronic quantum coherences, which is induced by the complicated structure of PESs. It directly manifests the complex interplay of excitonic coupling and the vibronic interactions of modes in both cases of pentacene and tetracene models. Thus, we demonstrate that the timescale of population transfer and the complicated coherent dynamics can be captured by our unified model.