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Chemical Sensing

Chemistry In Pictures

Chemistry in Pictures: Picture-perfect porphyrin

by Alexandra A. Taylor
January 28, 2021


A photo of a round-bottom flask containing a deep blue-green product and equipped with a reflux condenser sitting in a mineral oil bath.
Credit: Anna Christianson

Anna Christianson, a chemistry professor at Bellarmine University, was wowed by an exciting color change while making a sulfonated porphyrin (tetrakis(4-sulfonatophenyl)porphyrin or TSPP) to use as a reagent for an analytical chemistry teaching lab. Her starting material (tetraphenylporphyrin or TPP) was a vibrant purple as a solid. But after it dissolved in sulfuric acid, the color changed to deep green mixed with an iridescent blue-green. The iridescence faded over time, yielding a dark green final product. Christianson says the iridescence likely had to do with small solid particles of undissolved, unreacted TPP reflecting their color through the green solution. “This was my first experience with a porphyrin synthesis reaction, so I was certainly not disappointed with its exciting colors,” Christianson says. “Too bad the students won’t see it!” Christianson plans for her students to use the reagent as a colorimetric sensor for aqueous copper ions.

Submitted by Anna Christianson

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