Toward a Charged Homo[2]catenane Employing Diazaperopyrenium Homophilic Recognition

An
octacationic diazaperopyrenium (DAPP2+)-based homo­[2]­catenane
(DAPPHC8+), wherein no fewer
than eight positive charges are associated within a mechanically interlocked
molecule, has been produced in 30% yield under ambient conditions
as a result of favorable homophilic interactions, reflecting a delicate
balance between strong π–π interactions and the
destabilizing penalty arising from Coulombic repulsions between DAPP2+ units. This DAPPHC8+ catenane is composed of two identical mechanically interlocked tetracationic
cyclophanes, namely DAPPBox4+, each of which contains one
DAPP2+ unit and one extended viologen (ExBIPY2+) unit, linked together by two p-xylylene bridges.
The solid-state structure of the homo­[2]­catenane demonstrates
how homophilic interactions play an important role in the formation
of DAPPHC8+, in which the mean
ring planes of the two DAPPBox4+ cyclophanes are oriented
at about 60° with respect to each other, with a centroid-to-centroid
separation of 3.7 Å between the mean planes of the outer ExBIPY2+ and inner DAPP2+ units, and 3.6 Å between
the mean planes of the two inner DAPP2+ units. We show
that irradiation of the DAPPHC8+ catenane at 330 nm in acetonitrile solution results in simultaneous
energy and electron transfer. The latter occurs from the inner DAPP2+ dimer to the outer ExBIPY2+ unit, leading to
the generation of a temporary charge-separated state within a rigid
and robust homo­[2]­catenane. Compared to DAPPBox4+, both forward- and back-electron transfer
in DAPPHC8+ occur with faster
rates, owing to the closer proximity between the electron donor and
acceptor in the homo­[2]­catenane than in the separated
cyclophane.