Optical Properties of Disilane-Bridged Donor–Acceptor Architectures: Strong Effect of Substituents on Fluorescence and Nonlinear Optical Properties

A series of disilane-bridged
donor–acceptor architectures 1–9 containing strong electron-donating
and -withdrawing substituents were designed and synthesized in acceptable
yields. The substituents substantially affected the fluorescence and
nonlinear optical properties of the compounds. In the solid state,
the compounds showed purple–blue fluorescence (λem = 360–420 nm) with high quantum yields (up to 0.81).
Compound 3, which had p-N,N-dimethylamino and o-cyano substituents,
exhibited optical second harmonic generation (activity 2.9 times that
of urea, calculated molecular hyperpolarizability β = 1.6 ×
10–30 esu) in the powder state. Density functional
theory calculations for the ground and excited states indicated that
both the locally excited state and the intramolecular charge transfer
excited state make important contributions to the luminescence behavior.