Present calculations provide a theoretical understanding of the correlation of the conformations of tetramethyltetraphenylcyclotetrasiloxane with the properties of the ground states (S0-state) and excited states (S1-/T1state), as well as with the formation of the excimers. The difference between the energy-lowest conformation and the energy-highest conformation is only 0.51 kcal/mol. The isoenergetic conformers have similar electronic structures and absorption spectra. The difference between the vertical transition and the adiabatic transition in energy is relatively large for S1-states, but negligible for T1-states. The singlet-triplet gap for the adiabatic transition is very small (0.52 eV). The excited transition of the singlet electron may cause the geometrical deformation of S0-states, and the distorted phenyl ring is the excimer-forming site. The type of the excitation transition is associated with the conformation. The cooperation of the S0-states to the S1-states through the π-π or π-H interaction is a nonspontaneous-endothermic process. The formation and stability of the excimers are dependent upon the conformation.