Influence of laser wavelength and pulse duration on the degradation of polymeric films embedding photochromic molecules

An extensive investigation of the photodegradation of the photochromic molecule 1′,3′-dihydro-1′,3′,3′-trimethyl-6-nitrospiro[2H-1-benzopyran-2,2′-(2H)-indole] in a polymer matrix is studied under irradiation with ultraviolet (UV) laser pulses of 248 and 308 nm wavelength. Apart from the effect of the wavelength, the effect of the pulse duration is also presented using pulses of 30 ns and 500 fs for the 248 nm wavelength. To tackle the problem of oxidative degradation upon irradiation of the photochromic molecules which is known to play a principal role in the photodegradation process, we incorporate Iron(II) phthalocyanine molecules in the examined matrices. These molecules upon UV irradiation are dissociated into photoproducts that can interact efficiently with electron acceptor groups in the polymer, partly responsible for the photochromic degradation. The phthalocyanine molecules seem to protect efficiently the photochromic molecules only at low laser fluences. Moreover, in the case of ultrashort pulses the degradation of the photochromic molecules is found to be more intense that in the case of ns pulses, indicating multiphoton absorption mechanisms, unless low laser fluences are used.