The origin of third order nonlinear optical effects in polysilanes

Abstract

Summary form only given. The origins of the third order susceptibility in the lowest excited singlet state of the polysilanes are discussed. In particular singlet-singlet, singlet-triplet absorption, fluorescence and phosphorescence spectra of poly(di-n-hexylsilane) have been examined. The spectra are consistent with an assignment of the lowest excited singlet state to an excitonlike state of a linear chain. Photochemical hole-burning experiments have also been performed in this system. The changes in the absorption spectra induced by photochemistry are also consistent with an excitonic lowest singlet state. Photochemical induced structure was also observed in the absorption spectrum. This structure is consistent with the exitonic nature of the lowest singlet state, arising from structure in the expected absorption of excitons restricted to short chains (less than 10 atoms). A pronounced decrease in the third order susceptibility is observed upon heating the sample above 42° C. The change in susceptibility is consistent with the breaking up of the exciton chain at higher temperatures.