Submitted by Matthew Riehl / Minnesota State University, Mankato on Mon, 11/18/2019 - 16:30
My Notes

The UV-vis spectra of porphyrins are among the most recognizable spectra in the chemical literature, but the electronic transitions that lead to the observed specta are not as well known.  This presentation provides an introduction to the structure and numbering of porphyrins and the origin of the bands observed in the near UV and visible region, based on the work done by Martin Gouterman beginning in the late 1950's.    

Attachment Size
The Origins of Porphyrin UV-Vis Spectra 898.63 KB
Learning Goals

The student will…

•understand the porphyrin core structure, the numbering, and naming schemes of porphyrins
•demonstrate that the porphyrin is aromatic, obeying the Hückel 4n+2 rule where n=4.
•recognize the key features of the porphyrin UV-Vis spectra: the Soret Band and the Q-bands
•qualitatively describe Gouterman’s four-orbital model to explain the spectra.


Implementation Notes

This LO was begun at a VIPEr workshop at a regional ACS meeting.  It has not been used in my class, however we do make TPP and CuTPP.  The LO compliments the material I provide to my students and will be presented during the pre-lab discussion of the lab.  It should require about 15 minutes of time.

This author (M. Riehl) has learned that there is no simple explanation for the origins of the Soret and Q-bands in porphyrins and that there are still papers discussing the spectra of porphyrins and similar compounds appearing in the literature.

Time Required
15 minutes
Creative Commons License
Attribution, Non-Commercial, Share Alike CC BY-NC-SA