Reversible reactions are crucial for inducing crystallinity, as they enable continuous 'error correction' during the assembly of building blocks, ultimately leading to a thermodynamically equilibrated crystalline structure. However, COFs synthesized via reversible reactions often exhibit instability, as their linkages are susceptible to hydrolysis in solvents or harsh acidic/basic conditions. In contrast, COFs formed through irreversible reactions yield significantly more robust structures. The crystallinity of such COFs can be controlled by choosing the right precursors. Yaghi and co-workers had introduced irreversible aromatic nucleophilic substitution (SNAr) reactions for COF formation. Even though, the COFs are synthesised by irreversible reactions, they have crystallinity because it has annulated linkages which lead to a single possible conformation. This approach of using irreversible reactions is particularly crucial in the realm of cathode material fabrication since the material must withstand harsh conditions over multiple cycles.