Julian M. E-mail: bein lmu. Covalent organic frameworks COFs define a versatile structural paradigm combining attractive properties such as crystallinity, porosity, and chemical and structural modularity which are valuable for various applications.
For the incorporation of COFs into optoelectronic devices, efficient charge carrier transport and intrinsic conductivity are often essential. By condensing this unit with either terephthalaldehyde TA or benzodithiophene dialdehyde BDT , COFs featuring a dual-pore kagome-type structure were obtained as highly crystalline materials with large specific surface areas and mesoporosity. In addition, the experimentally determined high conduction band energies of both COFs render them suitable candidates for oxidative doping.
The incorporation of a benzodithiophene linear building block into the COF allows for high intrinsic macroscopic conductivity. Both anisotropic and average isotropic electrical conductivities were determined with van der Pauw measurements using oriented films and pressed pellets, respectively. Furthermore, the impact of different dopants such as F 4 TCNQ, antimony pentachloride and iodine on the conductivities of the resulting doped COFs was studied. By using the strong organic acceptor F 4 TCNQ, a massive increase of the radical cation density up to 0.
Interestingly, no significant differences between isotropic and anisotropic charge transport were found in films and pressed pellets. This work expands the list of possible building nodes for electrically conducting COFs from planar systems to twisted geometries.
The achievement of high and stable electrical conductivity paves the way for possible applications of new COFs in organic opto electronics. Recently, several two-dimensional 2D COFs with enhanced electrical conductivity were reported. The previously described two design strategies have been implemented for constructing 2D COF systems based on planar linkers such as pyrene, 10 tetrathiafulvalene, 22 phthalocyanine 21 or fully aromatic pyrazine systems. Chemical doping of these systems with oxidants serving as guest-molecules in the pores led to a further increase in electrical conductivity.
