Synthesis of crystalline two-dimensional conjugated polymers through irreversible chemistry under mild conditions

Two-dimensional conjugated polymers (2DCPs) are a class of monolayer to multilayer crystalline polymeric materials with conjugated linkages at two-orthogonal directions that promise applications from membranes to electronics. Current interfacial synthesis methods have succeeded in constructing 2DCPs from dynamic covalent chemistry, e.g., imine linkages. However, these methods are unsuitable for fabricating the 2DCPs of robust olefin linkages due to the inadequate reversibility. Here we report the synthesis of 2DCPs linked by olefin bonds via amphiphilic-pyridinium-assisted aldol-type interfacial polycondensation. The synthesis is achieved by an alkyl-quaternized trimethylpyridine that can self-assemble into ordered monolayer at water interface and further react in situ with multifunctional aldehydes via aldol-type topologic polycondensation. The resultant 2DCPs show long-range molecular ordering, large lateral size and well-controlled thickness. Both experimental and theoretical analyses show that the pre-assembled trimethylpyridinium monolayer at water interface significantly boosts its condensation reactivity, thereby facilitating the synthesis of 2DCPs under mild conditions. The integration of the 2DCPs with inherent positive charges in an osmotic power generator gives excellent output power density reaching 51.4 W m-2, superior to the most reported 2D nanoporous membranes.