Ab initio molecular design of third-order nonlinear optical susceptibilities of polysilanes

Third-order nonlinear optical susceptibilities (chi) (3) of polysilanes were estimated both at molecular and crystalline levels, in order to establish a molecular design strategy of (chi) (3) of polysilanes, by using an ab initio coupled perturbed Hartree-Fock (CPHF) method and the oriented-gas approximation. Molecular calculation results showed the main chain conformation of polysilanes directly affects second hyperpolarizabilities (gamma) of polysilane oligomers, and the trans planar oligomers have larger (gamma) than the 7/3 helical or alternating trans gauche (TGTG') oligomers, due to a stronger (sigma) -electron delocalization in their trans planar main chain. On the other hand, it was found that crystalline (chi) (3) of polysilanes are influenced not only by the main chain confirmation, but also by the molecular weight of polysilane repeating unit MSi. Based on those molecular and crystalline results, a strategy of molecular design of polysilane (chi) (3) was proposed which predicts trans planar poly[dimetylsilane] may have the largest (chi) (3) among polysilanes investigated so far, owing to its trans planar main chain and smallest MSi.

[1]  Wong,et al.  Nonlinear optical properties of linear chains and electron-correlation effects. , 1988, Physical review. B, Condensed matter.

[2]  Ray H. Baughman,et al.  Optical Nonlinearities in One-Dimensional-Conjugated Polymer Crystals. , 1976 .

[3]  Mark S. Gordon,et al.  Self‐consistent molecular orbital methods. XXIII. A polarization‐type basis set for second‐row elements , 1982 .

[4]  Mark C. Jurich,et al.  Temperature dependence of the third‐order nonlinear optical susceptibilities in polysilanes and polygermanes , 1988 .

[5]  Bernard Kirtman,et al.  AB INITIO FINITE OLIGOMER METHOD FOR NONLINEAR OPTICAL PROPERTIES OF CONJUGATED POLYMERS : NONRESONANT FREQUENCY DISPERSION IN POLYACETYLENE , 1996 .

[6]  Francois Kajzar,et al.  Nonlinear optical properties of thin films of polysilane , 1986 .

[7]  J. F. Rabolt,et al.  Studies of the conformation and packing of polysilanes , 1993 .

[8]  T. Hamada,et al.  The sum of hyperpolarizabilities approach to third-order non-linear optical susceptibilities of π-conjugated polymer crystals , 1996 .

[9]  Michel Dupuis,et al.  Ab initio analytic polarizability, first and second hyperpolarizabilities of large conjugated organic molecules: Applications to polyenes C4H6 to C22H24 , 1988 .

[10]  M. Piqueras,et al.  Theoretical study of the effect of substituent and backbone conformation on the electronic properties of symmetrically substituted poly(di‐n‐alkylsilanes) , 1994 .

[11]  Tachibana,et al.  Spectra of one-dimensional excitons in polysilanes with various backbone conformations. , 1993, Physical review. B, Condensed matter.

[12]  Bernard Kirtman,et al.  Ab initio finite oligomer method for nonlinear optical properties of conjugated polymers. Effect of electron correlation on the static longitudinal hyperpolarizability of polyacetylene , 1995 .