Highly CrystallineSemiconducting Tetrathienonaphthalene-BasedCovalent Organic Frameworks with Oblique Lattice

Highly crystalline semiconducting covalent organic frameworks (COFs) were synthesized from two isomeric tetrathienonaphthalene (TTN) nodes via transimination polymerization. The use of functionalized Schiff-base monomers proved critical for overcoming the low solubility of TTN-tetracarbaldehydes, enabling the solvothermal synthesis of four imine COFs with phenyl or biphenyl linkers. Systematic optimization of amine precursors yielded COFs with very high crystallinity (fwhm1002θ ≈ 0.26°) and porosity (BET surface area up to ∼1660 m2/g). Powder X-ray diffraction combined with DFT modeling revealed oblique lattice stacking and allowed experimental distinction between s-Z and s-E conformations of the imine linkage. Thin films grown on ITO substrates were used to fabricate bilayer photovoltaic diodes with a nonfullerene acceptor IT-4F. Although luminescence quenching (∼50%) suggests appreciable charge separation in these heterojunctions, the power conversion efficiency (0.1%–0.2%) was limited by the low charge mobility of the COF film.