title: Aggregation effects on the optical emission of 1,1,2,3,4,5-hexaphenylsilole (HPS): a QM/MM study.
abstract: We investigate the photophysical property for 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 the 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. The intermolecular packing effect is incorporated through electrostatic interaction modeled by a force field. We find that from the gas phase to the solid state (i) the side phenyl ring at the 5-position becomes coplanar with the central silacycle, which increases the degree of conjugation, thus accelerating the radiative decay process, and (ii) the rotation of the side phenyl ring at the 2-position is restricted, which blocks the excited-state nonradiative decay channels. Such a synergetic effect largely enhances the solid-state 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 addition, the calculated solid-phase absorption and emission optical spectra of HPS are found to be in agreement with the experiment.
authors.affiliation: Key Laboratory of Organic OptoElectronics and Molecular Engineering, Department of Chemistry, Tsinghua University , Beijing 100084, P. R. China.
authors.forename: Tian
authors.initials: T
authors.lastname: Zhang
authors.forename: Yuqian
authors.initials: Y
authors.lastname: Jiang
authors.forename: Yingli
authors.initials: Y
authors.lastname: Niu
authors.forename: Dong
authors.initials: D
authors.lastname: Wang
authors.forename: Qian
authors.initials: Q
authors.lastname: Peng
authors.forename: Zhigang
authors.initials: Z
authors.lastname: Shuai