PHOTOBLEACHING PROCESS IN POLYSILANE FILMS

The thermally assisted photoscission model has been formulated to expl ain the photobleaching of polysilane films due to the photoinduced ann ihilation of sigma bonds. In the model, sigma bonds are photoexcited a nd then scissored with thermal assistance, and the photobleaching by m eans of a prolonged exposure to ultraviolet light leads to the formati on of a sponge-like structure. The model predicts that (i) the decay o f the photon flux absorbed in the films after t(T), defined as the tim e when the transmittance of the films begins to increase significantly , obeys a power law with an exponent of gamma = kT/epsilon(0), where e psilon(0) is the exponential width of the activation-energy distributi on and kT is the thermal energy; (ii) t(T) is inversely proportional t o the incident photon flux and obeys a power law against the film thic kness with an exponent of 1/gamma; and (iii) the temperature dependenc e of t(T) provides the cross section of the photoexcitation of sigma b onds C-r. It has been confirmed that these predictions are fairly cons istent with the experimental results. The parameters of epsilon(0) and C-r for the photobleaching of poly(methylphenylsilane) films by 325 n m light have also been estimated to be 28 meV and 1.1 x 10(-16) cm(2), respectively.