Damped oscillations in UV-vis spectra of pentazadiene monomers and polymers after laser photolysis

The photochemical decomposition of substituted 1,5-diaryl-3-alkyl-pentazadi ene monomers and polymers induced by UV irradiation with a pulsed excimer l aser was monitored by UV-vis spectroscopy. The net photochemical reaction p roceeds in an overall one-step pathway A-->B. Quantum yields for the laser decomposition are determined to be less than or equal to 10%. An oscillatin g behavior of the absorption was found during the dark period following the irradiation. The temperature dependence of this dark reaction has been stu died. The oscillatory behavior is discussed in the light of current theorie s concerning instabilities in photochemical systems.