Postsynthetic Systematic Electronic Tuning of Organoplatinum Photosensitizers via Secondary Coordination Sphere Interactions

In this work we show
that postsynthetic addition of borane Lewis
acids to Lewis base decorated organoplatinum photosensitizers induces
significant changes in the optical and electrochemical properties.
In particular, the charge transfer (CT) energies of these chromophores
are significantly modified by these outer-sphere interactions. The
direction of the CT shift depends on the site of Lewis acid binding,
which occurs either at the diimine ligand in bipyrazine-linked molecules
or at an ancillary acetylide ligand in pyridyl-substituted bis­(acetylide)
molecules. The magnitude of the shift depends on the Lewis acidity
of the borane and the number of equivalents added and is comparable
to the perturbation brought on by covalent substituent modification
of supporting ligands in related complexes. This approach offers a
new means of tuning the properties of organometallic phosphors that
complements the traditional approach of covalent modification and
other postsynthetic modification strategies.