Song-Liang Cai,# Yue-Biao Zhang,# Andrew B. Pun, Bo He, Jinhui Yang, Francesca M. Toma, Ian D. Sharp, Omar M. Yaghi, Jun Fan, Sheng-Run Zheng, Wei-Guang Zhang,* and Yi Liu*
Chem. Sci.2014, 5, 4693-4700
Despite the high charge-carrier mobility in covalent organic frameworks (COFs), the low intrinsic conductivity and poor solution processability still impose a great challenge for their applications in flexible electronics. We report the growth of oriented thin films of a tetrathiafulvalene-based COF (TTF-COF) and its tunable doping. The porous structure of the crystalline TTF-COF thin film allows the diffusion of dopants such as I2 and tetracyanoquinodimethane (TCNQ) for redox reactions, while the closely packed 2D grid sheets facilitate the cross-layer delocalization of thus-formed TTF radical cations to generate more conductive mixed-valence TTF species, as is verified by UV-vis-NIR and electron paramagnetic resonance spectra. Conductivity as high as 0.28 S m−1 is observed for the doped COF thin films, which is three orders of magnitude higher than that of the pristine film and is among the highest for COF materials.