Rational Design Strategy for the Synthesis of Hyper-Cross-Linked Polymers Using Dipolar π-Systems and Proton Sorption Induced Pseudocapacitance

Hyper-cross-linked polymers (HCPs) are one of the important classes of porous organic polymers and are known for their easy preparation under mild conditions by employing readily available precursors. Though there are many HCPs synthesized out of electron-rich π-systems, literature reports of HCPs with π-systems having electron-deficient functional groups such as imides are sparse. This is challenging due to the inherent inefficient nature of Friedel–Crafts alkylation on π-systems with electron-deficient functional groups. In this study, we report a rational strategy for the synthesis of HCPs using benzoperylene imide (BPI) based dipolar π-systems via Friedel–Crafts alkylation. This is achieved by attaching a phenylbutane chain at the imide position, in which the phenyl ring of the phenylbutane serves as the site for Friedel–Crafts alkylation. The resultant BPI-HCP-I exhibits a Brunauer–Emmett–Teller surface area of 544 m²/g and strong visible-light absorption up to 600 nm. On the other hand, HCPs synthesized without any phenyl ring at the imide side chain (BPI-HCP-II and BPI-HCP-III) exhibit poor surface area due to inefficient cross-linking via Friedel–Crafts alkylation. Interestingly, BPI-HCP-I showed good electrochemical performance, exhibiting a specific capacitance of 112 F/g, highlighting its reversible proton storage capability. Our study provides the pathway for the synthesis of HCPs with large dipolar π-systems, which are good candidates for strong visible-light absorption and energy storage applications.