An Electrically Conductive Tetrathiafulvalene-Based Hydrogen-Bonded Organic Framework

Abstract

Recent advancements in the development of conductive metal− organic frameworks (MOFs) and covalent organic frameworks (COFs) have sparked interest in a variety of applications that leverage electronic materials due to the inherent tunability, porosity, and crystallinity associated with these materials. Hydrogen-bonded organic frameworks (HOFs) comprise an emerging class of complementary porous materials that assemble crystalline networks mainly from intermolecular hydrogen-bonding interactions; however, relatively few reports on functional HOFs exist as these reversible interactions are much weaker than the coordination or covalent bonds found in the former frameworks, which presents additional challenges in the isolation and activation of HOFs. In this work, we introduce an approach to access a permanently porous HOF derived from a tetrathiafulvalene (TTF) core, which is the first HOF reported to date that exhibits electrical conductivity. Upon precipitation from solution, HOF-110 self-assembles in a preferred orientation that contains vertical columns of TTF dimers, and the postsynthetic incorporation of iodine within the nanoporous channels of this framework affords pressed pellet conductivity values of up to 6.0 × 10 −7 S•cm −1 , which is an almost 30-fold improvement compared with pressed pellets of the pristine framework. Extensive structural characterization studies suggest the presence of radical mixed-valence TTF/TTF •+ species within these materials, which is consistent with previous reports on analogous TTF-based MOFs and COFs. Overall, this work presents a viable strategy to develop robust, electrically conductive frameworks built from purely intermolecular interactions, further expanding the toolbox available for the assembly of functional porous materials.

Design Rules of Hydrogen-Bonded Organic Frameworks with High Chemical and Thermal Stabilities

“…Through the rational design of organic building blocks with geometric symmetry, planar molecules with diverse π-conjugated systems can coordinate to each other through intermolecular H-bonding interactions to form a single layer, and multiple layers pack together through strong π–π-stacking interactions to form a 3D framework with one-dimensional (1D) channels throughout the structure. HOFs that contain large, π-conjugated aromatic molecules as building blocks exhibit significantly enhanced thermal stabilities and increased chemical resistance to organic solvents and acidic or basic aqueous solutions due to the inert reactivity of the tectons (Figure ) (see refs , , , , , , − , − , − , , , , , , , − , , , , , − , , , − ). Several groups have independently demonstrated that HOFs with shape-fitted π–π-stacking interactions not only show type III stability upon desolvation but also become even more stable as the effective π–π-stacking areas become larger (Table ).…”

Semiconductor Porous Hydrogen-Bonded Organic Frameworks Based on Tetrathiafulvalene Derivatives

“…Transport measurements for MUV-20a , MUV-20b , and MUV-21 were performed using two-contact probe pressed-pellet devices measured at room temperature (300 K) (Figure S46), revealing conductivity values of 6.07 × 10 –7 , 1.35 × 10 –6 , and 6.23 × 10 –9 S cm –1 , respectively (see Table S11). This indicates that MUV-20a and MUV-20b behave as semiconductors, presenting electrical conductivities similar to those reported for Cd 2 (TTFTB) and TTF-COF after being oxidized with iodine and more than 10 times higher than iodine-doped HOF-110 (see Table S12 for comparative values with all reported MOFs and HOFs containing the TTFTB unit). In contrast, non-zwitterionic MUV-21 behaves as an insulator due to the absence of charge carriers.…”

“…41 A very recent development in TTFbased HOFs has been shown by Farha and co-workers, who have prepared a HOF with a naphthalene derivative of TTF, which, upon oxidation with I 2 , becomes a semiconductor (conductivity of 6.0 × 10 −7 S cm −1 ). 42 Herein, we present the use of the H 4 TTFTB molecule to prepare two new porous HOFs, in which the building block ligand has a zwitterionic character. These materials, denoted MUV-20a and MUV-20b, do not require additional doping for electrical charge transport, resulting in two porous conducting HOFs while preserving their crystalline porosity.…”

“…This ligand has also been employed in the construction of a HOF with limited stability, which collapses upon desolvation, and more recently, it has shown to be involved in single-crystal-to-single-crystal transformations . A very recent development in TTF-based HOFs has been shown by Farha and co-workers, who have prepared a HOF with a naphthalene derivative of TTF, which, upon oxidation with I 2 , becomes a semiconductor (conductivity of 6.0 × 10 –7 S cm –1 ) …”

Functionalization of a stable AIE-based hydrogen-bonded organic framework for white light-emitting diodes

“… 20 Farha and co-workers reported post-synthetic incorporation of iodine within conductive HOF-110 affording a 30-fold improvement in electrical conductivity. 35 Sun and Luo et al proposed to load the doxorubicin onto the surface of a porphyrin-based HOF, which provided synergistic chemotherapy–photodynamic therapy–photothermal therapy effects. 36 These works inspire us to construct functionalized HOFs for the application of white light-emitting diodes (WLEDs) which is difficult to be achieved by a HOF material itself.…”