Electron Hopping and Charge Separation within a Naphthalene-1,4:5,8-bis(dicarboximide) Chiral Covalent Organic Cage

We present the stereoselective synthesis
of a chiral covalent organic
cage consisting of three redox-active naphthalene-1,4:5,8-bis­(dicarboximide)
(NDI) units by dynamic imine chemistry. Single crystal X-ray diffraction
analysis shows that host–guest interactions and racemic cocrystallization
allow for controlling the solid state structure. Electronic interactions
between the NDI units probed by absorption and circular dichroism
spectroscopies, electrochemistry and theoretical calculations are
shown to be weak. Photoexcitation of NDI leads to intracage charge
separation with a longer lifetime than observed in the corresponding
monomeric NDI and dimeric NDI cyclophane imines. The EPR spectrum
of the singly reduced cage shows that the electron is localized on
a single NDI unit at ambient temperatures and transitions to rapid
hopping among all three NDI units upon heating to 350 K. Dynamic covalent
chemistry thus promises rapid access to covalent organic cages with
well-defined architectures to study charge accumulation and electron
transport phenomena.