The spectral stability of three guest molecules embedded in a quickly frozen n-tetradecane matrix has been investigated on a single-molecular level at liquid-helium temperature. In total, about 2500 spectral trajectories of 476 terrylene molecules, 328 dibenzanthanthrene molecules, and 252 pentacene molecules were recorded. Both line broadening and spectral jumps are analyzed and the latter are found to be mainly light induced. The spectral changes in essence reflect the dynamics of the host matrix and the differences between the guest molecules may be reduced to differences in their pumping cycles.