The Fully Conjugated 3D COFs:the Synthesis And Research On It’s Photoelectric Properties

Covalent organic frameworks(COFs)materials have been widely used in energy storage,separation,catalysis,optoelectronic devices and many other fields due to their good crystallinity,high porosity,and diverse structural and functional designs.Among them,the fully conjugated 3D COFs have more complex interpenetrated structure and can transfer charge in the whole three-dimensional framework,which has more advantages in photoelectric and other applications.However,due to the lack of 3D fullyπ-conjugated linkers,most of the 3D COFs reported at present are incomplete conjugated materials,which limits their application to a large extent.Therefore,a three-dimensional fully sp2 carbon-conjugated linker is designed and two fully π-conjugated 3D COFs are synthesized in this paper.1.This paper designed and synthesized an aldehyde-substituted cyclooctatetra-thiophene(COThP-CHO)building block with saddleshaped structure,it has a sp2 π-electron conjugated three-dimensional framework,which can be used as a linker to design and synthesize fully πconjugated 3D COFs.In this paper,a fully π conjugated 3D COFS material BUCT-COF-1 with high crystallinity was firstly synthesized from saddle COTHP-CHO and 1,4-diaminobenzene(DAB)by reversible Schiff base polycondensation reaction.Through a series of characterization and system analysis,it shows that BUCT-COF-1 has a 13-fold-interpenetrated diamond(dia-c13)topology structure,and exhibited band-like transport with high electron mobility,posses the n-type semiconductor properties.At room temperature(298 K),calculated the charge carrier density was 3.40×1010 cm-3,the conductivity was 1.51 ×10-8 S/cm,The Hall electron mobility in the d.c.limit was 2.75 cm2/(V s),exhibits the highest value at the range of～3.0 cm2/(V s),which is one order of magnitude higher than these of current n-type semiconductor 2D COFs.The charge transport mechanism of BUCT-COF-1 was further investigated,The temperature dependent conductivity measurement results show that the charge carriers in BUCT-COF-1 exhibit the band-like transport mechanism which is completely different from the hopping-type transport phenomenon in common organic semiconducting materials.2.In order to further expand the 3D COFs materials applied in the field of optoelectronic devices,etc.this article synthesized a fully sp2 carbon conjugated 3D COFS material BUCT-COF-4 with greater π-πconjugate system used COThP-CHO as a linker again,reacted with phenylenediacetonitrile(PDAN)via Knoevenagel condensation reaction.compared with the imine-linked COFs,BUCT-COF-4 has a greater π-πconjugate system,and stability of the C=C linked COFs is better,so that it has more advantages in the field of photoelectricity and other applications.This article explored the synthesis conditions of BUCT-COF-4,the experimental results show that BUCT-COF-4 also exhibited band-like transport with high electron mobility,posses the n-type semiconductor properties.at room temperature(298 K),calculated the chage carrier density was 1.81 × 1011 cm-3,the conductivity was 5.41 × 10-8 S/cm,higher than BUCT-COF-1,The Hall electron mobility in the d.c.limit was 1.97 cm2/(V s).It is also one order of magnitude higher than these of current n-type semiconductor 2D COFs.The successful preparation of BUCTCOF-4 has promoted the development of fully conjugated threedimensional covalent organic frame materials in optoelectronics and other fields.