In this paper we present a theoretical study of coherent optical effects such as optical free induction decay (OFID) and photon echoes (PE) from an ensemble of collision-free large molecules. We have introduced a generalized effective hamiltonian to account for the temporal characteristics of the macroscopic polarization. Explicit results have been obtained for the OFID and PE under short-time on-resonance optical pulsed excitation elucidating the nature of phase destruction effects originating from intramolecular interstate and intrastate coupling and from inhomogeneous broadening effects.