Compound 1 as Actinometer

The reversible photocyclization reaction which compound 1 undergoes when irradiated with UV or visible light, offers the possibility to use it as a chemical actinometer. Its positive features are  

Therefore, compound 1 appears to be a very convenient, simple and reusable actinometer. 

Procedure—Compound 1 can be synthesized as indicated in [29]. An approximately 1 x lO mol solution of 1 is prepared in spectrophotometric grade acetonitrile and a known volume of this solution is put in a sealable quartz 

UV region. Read the absorbance at both the excitation wavelength and 600 nm, before and after irradiation. The increase in absorbance at 600 nm (0.1-0.2 is sufficient) enables the photon intensity incident in the cell to be calculated using the Eq. 4.31, 

For 2 340 nm, the molar absorption coefficient of lb is larger than that of la and so the fraction of light absorbed by lb is high even for small conversions (e.g., at 365 nm lb absorbs 59% of the light after 10% conversion). The use of 1 as actinometer in the 340-400 nm spectral region is, therefore, discouraged. 

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