Modeling of configurations and third-order nonlinear optical properties of methyl silsesquioxanes

Abstract

Configuration optimizations, excited state properties, and the frequency-dependent third-order nonlinear optical polarizabilities have been investigated on a series of methyl-silsesquioxane (MeT) cages [CH(3)SiO(1.5)](n) (n=4, 6, 8, and 10) using ab initio quantum mechanical methods coupled with the sum-over-states methods. The obtained electronic absorption spectra show a redshift as the cage size increases, and the absorption spectra are assigned as charge transfers from oxygen p type to silicon s type atomic orbitals. The calculated average third-order polarizabilities of <gamma> in the three optical physical processes (third-harmonic generation, the electric-field-induced second-harmonic generation, and degenerate four-wave mixing) have wide nonresonance regions. For all the considered species, the values of gamma decrease in the order of [MeT](4)>[MeT](8)(C(2v))=[MeT](10)>[MeT](6)>[MeT](8)(O(h)).

Photophysical Properties of Partially Functionalized Phenylsilsesquioxane: [RSiO1.5]7[Me/nPrSiO1.5] and [RSiO1.5]7[O0.5SiMe3]3 (R = 4-Me/4-CN-Stilbene). Cage-Centered Magnetic Fields Form under Intense Laser Light

“…Many recent theoretical studies describe HOMO–LUMO interactions in a wide variety of SQ macromonomers. − As a prelude to understanding the behavior of the corner-missing cage, we first did calculations for the permethyl cage as shown in Figure . The presence of a spherical LUMO that matches very closely those we have reported previously supports the existence of a similar LUMO in the Ph 7 T 8 R′ cages described above.…”

“…To understand the electronic properties of the Stil x T 7 -trisiloxy compounds, we calculated the HOMO–LUMO structures of the simplified Me 7 T 7 -trisiloxy analogue per Figure . From our results for Me 7 T 7 -trisiloxy molecule, the HOMO and LUMO energies are −7.37 and 0.91 eV, respectively; a gap of 8.34 eV similar to the theoretical model obtained by Shen et al…”

“…To understand the electronic properties of the Stil x T 7trisiloxy compounds, we calculated the HOMO−LUMO structures of the simplified Me 7 T 7 -trisiloxy analogue per Figure 14. From our results for Me 7 T 7 -trisiloxy molecule, the HOMO and LUMO energies are −7.37 and 0.91 eV, respectively; a gap of 8.34 eV similar to the theoretical model obtained by Shen et al 48 The LUMOs are again localized predominantly in the cage center. However, the LUMO appears to be asymmetric within the cage in keeping with the photomagnetic studies described above.…”

Lithium-Templated Formation of Polyhedral Oligomeric Silsesquioxanes (POSS)

“…Moreover, the enthalpy of formation (Δ r H °) of the proposed dumbbell-like-shaped structure was calculated to be −4.83 eV. Currently, computational studies have suggested that there is a large highest occupied molecular oribital–lowest unoccupied molecular orbital (HOMO–LUMO) gap in silsesquioxane cages. − To understand the electronic properties of the Li-T 7 structure, the HOMO and LUMO energies of Li-T 7 were calculated and found to be −7.25 and 0.23 eV, respectively. The HOMO–LUMO gap is around 7.48 eV and is similar to other silsesquioxange cages.…”

Ultrafast Excited-State Dynamics of Partially and Fully Functionalized Silsesquioxanes

“…There have also been extensive computational studies carried out on the electronic structure, electronic spectra, optical properties, and reactivity of T 8 octahedral SQs over the past two decades. − Phillips et al investigated the absorption excitation energy of functionalized octahedral SQs via time-dependent density functional theory. Using the B3LYP and RSH functional, they found that the excitations are mainly localized on the chromophores, except for vinylsilsesquioxane.…”