ABSTRACT
Over the last 40 years, magnetic circular dichroism (MCD) spec-
troscopy has provided many key insights into the optical spec-
troscopy and electronic structure of porphyrinoid compounds [1, 2].
In this chapter, the use of the technique, since the start of the
new millennium, to assign the optical spectra of newly synthe-
sized porphyrinoid ligands and to elucidate their electronic struc-
tures is described in depth. The recent emergence of DFT theo-
retical treatments in commercially available software packages has
made the calculation of detailed descriptions of the electronic struc-
tures of newly synthesized compounds routine. MCD spectroscopy
provides key additional information about band polarization and
state degeneracies, which can be used to validate time-dependent
density functional theory (TD-DFT) calculations and to test the
accuracy of density functional theory (DFT) descriptions of the
electronic structure. In this chapter, the theoretical background
to MCD spectroscopy and recent applications of the technique to
radially symmetric and low-symmetry synthetic porphyrinoids and
to bioinorganic complexes of transition metals, such as heme pro-
teins, are described in detail. The radially symmetric synthetic
porphyrinoids dealt with in this chapter include deeply saddled
compounds such as tetraphenyltetraacenaphthoporphyrins and
α-octaphenylphthalocyanines, ring-contracted subporphyrin and
[14]triphyrin(2.1.1) compounds, and expanded porphyrinoids with
both 4N and 4N+2 π -electron systems such as gold hexaphyrins. The low-symmetry compounds covered include core-modified tetra-
benzoporphyrins, corrolazines, fused-ring-expanded phthalocya-
nines, tetraazachlorins, azulene-fused porphyrins, azulenocyanines,
and benzoporphycenes.
