Tunable electrical conductivity in oriented thin films of tetrathiafulvalene-based covalent organic framework

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; Yi Liu

doi:10.1039/C4SC02593H

Tunable electrical conductivity in oriented thin films of tetrathiafulvalene-based covalent organic framework†

Song-Liang Cai,‡^ab Yue-Biao Zhang,‡^cd Andrew B. Pun,^a Bo He,^a Jinhui Yang,^de Francesca M. Toma,^ef Ian D. Sharp,^eg Omar M. Yaghi,^cd Jun Fan,^b Sheng-Run Zheng,^b Wei-Guang Zhang*^b and Yi Liu*^a

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* Corresponding authors

^a The Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
E-mail: yliu@lbl.gov

^b School of Chemistry and Environment, South China Normal University, Guangzhou 510006, P. R. China
E-mail: wgzhang@scnu.edu.cn

^c Department of Chemistry, University of California-Berkeley, Kavli Energy NanoSciences Institute at Berkeley, Berkeley, California 94720, USA

^d Material Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA

^e Joint Center for Artificial Photosynthesis, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA

^f Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA

^g Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA

Abstract

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.

Chemical Science

Tunable electrical conductivity in oriented thin films of tetrathiafulvalene-based covalent organic framework†

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Tunable electrical conductivity in oriented thin films of tetrathiafulvalene-based covalent organic framework

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