Effect of Ambient, Excitation Intensity and Wavelength, and Chemical Structure on Photodegradation in Polysilanes

Abstract

The photodegradation of a copolymer based on diphenyl and methylphenyl polysilane has been investigated by measuring the changes occurring in photoluminescence PL and absorption in solution and film form. In the solution, the degradation mechanism is photoscission of the Si–Si bonds, confirmed by gel permeation chromatography. In the films also, this mechanism exists but with a reduced rate due to cage effect. We are reporting an additional degradation mechanism, observed in the films, which is not sensitive to the environment. It is attributed to formation of defects or traps in the deformed segments of polysilane chain in film. Photodegradation rate is slower for the shorter wavelength emission/absorption due to occurrence of energy transfer from shorter to longer segments. In addition to degradation, the copolymer films exhibit an initial enhancement in PL intensity, which is attributed to the changes in chain conformation caused by heat generation during irradiation. We have also investigated the effect of chemical structure on photodegradation behavior by also evaluating poly n-butylphenylsilane , poly nhexylphenylsilane , poly n-octylphenylsilane , and poly bis p-n-butylphenyl silane polysilanes. The addition of bulky alkyl or aryl groups on both sides leads to improved stability with respect to photoscission, but degradation due to defect or trap creation persists even in solution, which is attributed to the differences in conformation of these polysilanes. Based on the experimental evidence, we present a physical model for degradation mechanisms operating in polysilanes. © 2007 American Institute of Physics