A Fully Conjugated 3D Covalent Organic Framework Exhibiting Band‐like Transport with Ultrahigh Electron Mobility

Abstract

Although π‐conjugated two dimensional (2D) covalent organic frameworks (COFs) have been extensively reported, developing fully π‐conjugated 3D COFs is still an extremely difficult problem due to the lack of fully π‐conjugated 3D linkers. We synthesize a fully conjugated 3D COF (BUCT‐COF‐1) by designing a saddle‐shaped building block of aldehyde‐substituted cyclooctatetrathiophene (COThP)‐CHO. As a consequence of the fully conjugated 3D network, BUCT‐COF‐1 demonstrates ultrahigh Hall electron mobility up to ≈3.0 cm2 V−1 s−1 at room temperature, which is one order of magnitude higher than the current π‐conjugated 2D COFs. Temperature‐dependent conductivity measurements reveal that the charge carriers in BUCT‐ COF‐1 exhibit the band‐like transport mechanism, which is entirely different from the hopping transport phenomena observed in common organic materials. The findings indicate that fully conjugated 3D COFs can achieve electron delocalization and charge‐transport pathways within the whole 3D skeleton, which may open up a new frontier in the design of organic semiconducting materials.

Saddle‐Shaped Building Blocks: A New Concept for Designing Fully Conjugated 3D Organic Semiconducting Materials

“…The LUMO and HOMO energy levels were calculated to be −3.51 eV and −5.45 eV, respectively by CV measurements. These parameters indicate that BUCT‐COF‐1 is a potential n‐type OSM and subsequent Hall effect experiments show that it has Hall electron mobility of ≈3.0 cm 2 V −1 s −1 at room temperature (in d.c. limit), exceeding most of the π‐conjugated 2D COFs reported previously [28,29] . Furthermore, the charge carriers in the BUCT‐COF‐1 show band‐like conduction, as confirmed by the variable‐temperature Hall effect measurements, completely different from the common OSMs in which the hopping transport phenomenon is dominated.…”

“…These parameters indicate that BUCT-COF-1 is a potential n-type OSM and subsequent Hall effect experiments show that it has Hall electron mobility of � 3.0 cm 2 V À 1 s À 1 at room temperature (in d.c. limit), exceeding most of the π-conjugated 2D COFs reported previously. [28,29] Furthermore, the charge carriers in the BUCT-COF-1 show bandlike conduction, as confirmed by the variable-temperature Hall effect measurements, completely different from the common OSMs in which the hopping transport phenomenon is dominated. These results elucidate that the 3D fully conjugated structure with highly long-range order could benefit the charge delocalization and transport for high electrical conductivity, and also further demonstrating that the fully conjugated 3D COF is a promising new type of OSMs.…”

“…Very recently, we have reported the first example of fully conjugated 3D COF (BUCT-COF-1) that was synthesized by reversible Schiff base polycondensation reaction of 1,4-diaminobenzene and saddle-like π-conjugated aldehyde-substituted COThP (COThPÀ CHO, Figure 5, synthesized via Scheme 1c). [28] The structure resolutions illuminate that the BUCT-COF-1 exhibits a diamond topology with a I4 1 /a space group and 13-fold interpenetration. Due to the high π-conjugation of the 3D framework, the BUCT-COF-1 has a broad absorption with an optical band gap of 1.94 eV.…”

“…The 3D covalent organic framework (COF) materials might be good alternatives to solve this issue, because they are usually highly crystalline with good level of long‐range order and their packing structure could be determined by simulation or single crystal analysis. Very recently, we have reported the first example of fully conjugated 3D COF (BUCT‐COF‐1) that was synthesized by reversible Schiff base polycondensation reaction of 1,4‐diaminobenzene and saddle‐like π‐conjugated aldehyde‐substituted COThP (COThP−CHO, Figure 5, synthesized via Scheme 1c) [28] . The structure resolutions illuminate that the BUCT‐COF‐1 exhibits a diamond topology with a I 4 1 / a space group and 13‐fold interpenetration.…”

Towards High‐Performance Resistive Switching Behavior through Embedding a D‐A System into 2D Imine‐Linked Covalent Organic Frameworks

“…Covalent organic frameworks (COFs) have emerged as a new class of 2D crystalline porous materials with unique designability with respect to topology diagram, pore environments, chemical structure and functionalities. COFs have been investigated into multifarious applications of gas adsorption and separation, [29–32] energy storage, [33–36] chemical sensors, [37–39] proton or ion conduction, [40–43] catalysis, [44–48] and some promising semiconductor devices [49–52] . Unfortunately, the research on nonvolatile resistive switching memory devices based on 2D COFs is still in its infancy.…”