Chiral Conjugated Corrals

We present here a
new design motif for strained, conjugated macrocycles
that incorporates two different aromatics into the cycle with an −A–B–A–B–
pattern. In this study, we demonstrate the concept by alternating
electron donors and acceptors in a conjugated cycle. The donor is
a bithiophene, and the acceptor is a perylene diimide derivative.
The macrocycle formed has a persistent elliptiform cavity that is
lined with the sulfur atoms of the thiophenes and the π-faces
of the perylene diimide. Due to the linkage of the perylene diimide
subunits, the macrocycles exist in both chiral and achiral forms.
We separate the three stereoisomers using chiral high-performance
liquid chromatography and study their interconversion. The mechanism
for interconversion involves an “intramolecular somersault”
in which one of the PDIs rotates around its transverse axis, thereby
moving one of its diimide heads through the plane of the cavity. These
unusual macrocycles are black in color with an absorption spectrum
that spans the visible range. Density functional theory calculations
reveal a photoinduced electron transfer from the bithiophene to the
perylene diimide.