A viologen-based UV indicator and dosimeter |
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Authors: | Mills Andrew McFarlane Michael Schneider Stefan |
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Institution: | (1) Department of Pure and Applied Chemistry, University of Strathclyde, Glasgow, G1 1XL, UK |
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Abstract: | A UV indicator/dosimeter based on benzyl viologen (BV2+) encapsulated in polyvinyl alcohol (PVA) is described. Upon exposure to UV light, the BV2+/PVA film turns a striking purple colour due to the formation of the cation radical, BV•+. The usual oxygen sensitivity of BV•+ is significantly reduced due to the very low oxygen permeability of the encapsulating polymer, PVA. Exposure of a typical
BV2+/PVA film, for a set amount of time, to UVB light with different UV indices produces different levels of BV•+, as measured by the absorbance of the film at 550 nm. A plot of the change in absorbance at this wavelength, ΔAbs(550), as
a function of UV index, UVI, produces a linear calibration curve which allows the film to be used as a UVB indicator, and
a similar procedure could be employed to allow it to be used as a solar UVI indicator. A typical BV2+/PVA film generates a significant, semi-permanent (stable for >24 h) saturated purple colour (absorbance ~0.8–0.9) upon exposure
to sunlight equivalent to a minimal erythemal dose associated with Caucasian skin, i.e. skin type II. The current drawbacks
of the film and the possible future use of the BV2+/PVA film as a personal solar UV dosimeter for all skin types are briefly discussed.
![MediaObjects/216_2006_605_Figa_HTML.gif](/content/fp004840808112g3/MediaObjects/216_2006_605_Figa_HTML.gif) |
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Keywords: | UV dosimeter UV indicator Methyl viologen Photoreduction |
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