The dipole moment of the molecule changes instantaneously after absorption of the photon. The solvent molecules are therefore in a arrangement consistent with the ground state dipole and not the excited state. What follows is that the solvent molecules reorient lowering the energy of the excited state.

The result is that the emitted light immediately following excitation is of short wavelength and higher energy than that which is emitted after solvent relaxation.

The time it takes for the spectrum to shift is identical to the relaxation time of the solvent because the solvent motion controls the relaxation.