SPECTRA OF ONE-DIMENSIONAL EXCITONS IN POLYSILANES WITH VARIOUS BACKBONE CONFORMATIONS

Linear and nonlinear optical spectra (one-photon and two-photon absorption, photoluminescence, and electroabsorption spectra) have been investigated for solid thin films of polysilanes with a variety of conformations, such as trans-planar, alternating trans-gauche (TGTG' type), 7/3 helical, and disordered backbone structures. Optical spectra have revealed features of one-dimensional exciton states characteristic of the respective conformations. In particular, the lowest allowed and second parity-forbidden (or two-photon allowed) transitions can be assigned to the ground (B-1(1u)) and first excited (1A(g)) states of one-dimensional Wannier-type exciton, respectively. Furthermore, the higher excited exciton states and subsequent band-to-band transitions show up in the electroabsorption spectra for polysilanes with various conformations of the Si backbones. Quantitative analysis based on a microscopic theory for the one-dimensional excitons is also presented.