Two-dimensional covalent organic frameworks (2D COFs)
feature graphene-type
2D layered sheets but with a tunable structure, electroactivity, and
high porosity. If these traits are well-combined, then 2D COFs can
be applied in electronics to realize functions with a high degree
of complexity. Here, a highly crystalline electroactive COF, BDFamide-Tp,
was designed and synthesized. It shows regularly distributed pores
with a width of 1.35 nm. Smooth and successive films of such a COF
were fabricated and found to be able to increase the conductivity
of an organic semiconductor by 103 by interfacial doping.
Upon encapsulation of a photoswitchable molecule (spiropyran) into
the voids of the COF layer, the resulted devices respond differently
to light of different wavelengths. Specifically, the current output
ratio after UV vs Vis illumination reaches 100 times, thus effectively
creating on and off states. The respective positive and negative feedbacks
are memorized by the device and can be reprogrammed by UV/Vis illumination.
The reversible photostimulus responsivity and reliable memory of the
device are derived from the combination of electroactivity and porosity
of the 2D COF. This work shows the capability of 2D COFs in higher-level
electronic functions and extends their possible applications in information
storage.