Tuning Optoelectronic Properties in Isoreticular Three-Dimensional Fully Conjugated Covalent Organic Frameworks

The emerging class of fully conjugated three-dimensional (3D) covalent organic frameworks (COFs) has attracted significant attention as a promising family of organic semiconductor materials. These materials possess a remarkable ability for π-electronic delocalization due to extended π-conjugation throughout the entire framework. Here, we report the synthesis of a phenyl-extended cyclooctatetrathiophene (COTh) core functionalized with amino groups. This functionalization represents a significant step forward in the development of this materials class, as amino groups offer great versatility for forming imine bonds with a variety of well-established linkers in traditional 2D COFs-such as thieno[3,2-b]thiophene-2,5-dicarboxaldehyde (TT) and benzo[1,2-b:4,5-b′]dithiophene-2,6-dicarboxaldehyde (BDT)-but have not yet been explored in 3D COFs. By employing modulator agents during the polycondensation step, highly crystalline frameworks were obtained. The porosity and intrinsic structural properties of the resulting thiophene-based, fully conjugated 3D COFs were verified by nitrogen adsorption, confirming the successful translation of the initial design into the final architectures. Furthermore, this study expands the scope to optoelectronic characterization, demonstrating the ability to precisely tune the optical bandgap within a range of ±0.19 eV and to modulate the redox behavior within the overall framework. Together, these advances highlight a robust strategy for engineering next-generation 3D COFs with programmable structure–property relationships.