[CrimpJiggler]

The class of compound I'm reading about is phthalocyanine:

The article mentions "meso atoms" on the phthalocyanine molecule. What is a meso atom, and which of phthalocyanines atoms would be considered meso atoms?

[Corribus]

The meso positions are the four outer nitrogens.  In a porphyrin, these are carbons.  The meso positions are distinguished from the beta positions and the alpha positions. The beta carbons are those which attach to the periphery phenyl groups in the phthalocyanine, and the alpha carbons are those that are each bonded to two nitrogens.  If you google "porphyrin meso position" you can find an image or two which show where these positions are.

[CrimpJiggler]

Thanks!