I'm looking for a tame biochemist who I can bother with silly molecular physics questions about chlorophyll and excited states and charge separation and things.
Can anyone help me out?
Synthetic photosensitisers have excitation mechanisms involving the metal centre. In Ruthenium tris-bipyridine, for instance, an electron on the Ru2+ atom is excited, and the charge is transferred to a ligand (MLCT) by intersystem crossing. Which means charge separation, etc, etc.
But Mg2+ has the same electron configuration as Ne, and effectively has no valence electrons. So what's the excitation mechanism when the metal centre is Mg? LMCT?
While Mg2+ has no valence electrons, Mg bound to the chlorin ligand scaffold is sharing plenty of electrons (getting a minimum of 6 or 8 electrons worth from the ligand depending on how you count 'em). The Mg center could be seen as effectively neutral.
The ligand itself is definitely able to do charge transfer, and from the (annoyingly sparse) literature available on a cursory search, I agree that something effectively MLCT is happening.
Hoping others join in here..
@GIMcGrew Thanks. I'm a little new to coordination chemistry, so I'm still figuring things out. It's logical that the 2+ charge would be shared across the whole delocalised structure...
Annoyingly sparse is right - I spent all afternoon trying to find something on this. Though TBH I can't really blame botanists from shying away from the detailed physics!
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