Inserting Nitrogen: An Effective Concept To Create Nonplanar and Stimuli-Responsive Perylene Bisimide Analogues

Establishing design principles to create nonplanar π-conjugated
molecules is crucial for the development of novel functional materials.
Herein, we describe the synthesis and properties of dinaphtho­[1,8-bc:1′,8′-ef]­azepine
bisimides (DNABIs). Their molecular design is conceptually based on
the insertion of a nitrogen atom into a perylene bisimide core. We
have synthesized several DNABI derivatives with a hydrogen atom, a
primary alkyl group, or an aryl group on the central nitrogen atom.
These DNABIs exhibit nonplanar conformations, flexible structural
changes, and ambipolar redox activity. The steric effect around the
central nitrogen atom substantially affects the overall structures
and results in two different conformations: a nonsymmetric bent conformation
and a symmetric twisted conformation, accompanied by a drastic change
in electronic properties. Notably, the nonsymmetric DNABI undergoes
unique structural changes in response to the application of an external
electric field, which is due to molecular motions that are accompanied
by an orientational fluctuation of the dipole moment. Furthermore,
the addition of a chiral Brønsted base to N-unsubstituted
DNABI affords control over the helical chirality via hydrogen-bonding
interactions.