We investigated the photophysical property for the 1,1,2,3,4,5-hexaphenylsilole(HPS)through combined quantum mechanical and molecular mechanical(QM/MM)simulations.Under the displaced harmonic oscillator approximation with consideration of Duschinsky rotation effect(DRE),the radiative and nonradiative rates of the excited-state decay processes for HPS are calculated by using the analytical vibration correlation function approach coupled with first-principles calculations for molecular parameters.The intermolecular packing effect is incorporated through electrostatic interaction with force field.We find that from gas phase to solid state(i)the side phenyl ring at the 5-position becomes coplanar with the central silacycle,which increases the degree of conjugation,thus accelerates the radiative decay process;(ii)the rotation of the side phenyl ring at the 2-position is restricted,which blocks the excited-state nonradiative decay channels.Such synergetic effect largely enhances the luminescence quantum efficiency through reducing the nonradiative decay rate by about 4 orders of magnitude,leading to the radiative decay overwhelming the nonradiatvie decay in solid state.The calculated solid-phase absorption and emission optical spectra of HPS are found to be in agreement with the experiment.