Covalent organic frameworks (COFs) with improved stability and extended pi-conjugation structure are highly desirable. Here, two imine-linked COFs were converted into ultrastable and pi-conjugated fused-aromatic thieno[3,2-c]pyridine-linked COFs (B-COF-2 and T-COF-2). The successful conversion was confirmed by infrared and solid-state C-13 NMR spectroscopies. Furthermore, the structures of thieno[3,2-c]pyridine-linked COFs were evaluated by TEM and PXRD. It is noted that a slight difference in the structure leads to totally different photoactivity. The fully pi-conjugated T-COF-2 containing triazine as the core exhibited an excellent photocatalytic NADH regeneration yield of 74% in 10 min.