jp5016824_si_001.pdf (2.79 MB)
Factors Controlling the Spectroscopic Properties and Supramolecular Chemistry of an Electron Deficient 5,5-Dimethylphlorin Architecture
journal contribution
posted on 2015-12-17, 03:02 authored by Allen
J. Pistner, Daniel A. Lutterman, Michael J. Ghidiu, Eric Walker, Glenn P. A. Yap, Joel RosenthalA new
5,5-dimethylphlorin derivative (3H(PhlCF3)) was prepared and studied through a combination of
redox, photophysical, and computational experiments. The phlorin macrocycle
is significantly distorted from planarity compared to more traditional
tetrapyrrole architectures and displays solvatochroism in the soret
region of the UV–vis spectrum (∼370–420 nm).
DFT calculations indicate that this solvatochromic behavior stems
from the polarized nature of the frontier orbital (LUMO+1) that is
most heavily involved in these transitions. Compound 3H(PhlCF3) also displays an intriguing supramolecular
chemistry with certain anions; this phlorin can cooperatively hydrogen-bond
two equivalents of fluoride to form 3H(PhlCF3)·2F– but does not bind larger
halides such as Cl– or Br–. Analogous
studies revealed that the phlorin can hydrogen-bond with carboxylate
anions such as acetate to form 1:1 complexes such as 3H(PhlCF3)·OAc–. These supramolecular
assemblies are robust and form even in relatively polar solvents such
as MeCN. Hydrogen-bonding of fluoride and acetate anions to the phlorin
N–H residues significantly attenuates the redox and photophysical
properties of the phlorin. Moreover, The ability to independently
vary the size and pKa of a series of carboxylate
hydrogen-bond acceptors has allowed us to probe how phlorin–anion
association is controlled by the anion’s size and/or basicity.
These studies elucidate the physical properties and the electronic
effects that shape the supramolecular chemistry displayed by the phlorin
platform.