Novel perylene-bridged polyethyleneimine polymer networks: synthesis and photophysical–electrochemical insights for supercapacitor applications

Abstract

In this work, we introduce a molecular design strategy to construct nitrogen-rich, π-conjugated, redox-active polymer networks using perylene-3,4,9,10-tetracarboxylic dianhydride as a multifunctional cross-linker for branched polyethyleneimine (PEI) for the first time. Two novel PEI–perylene networks, PEI-3 and PEI-5, were synthesised through imidization between the anhydride groups of the perylene precursor and the amine functionalities of PEI with molecular weights of 60 kDa and 25 kDa, respectively. The resulting insoluble networks combine PEI-derived nitrogen-rich domains with redox-active perylene imide/carbonyl units and π–π interacting conjugated segments. Structural, optical, morphological, thermal, and electrochemical properties were investigated using ¹H NMR, FTIR, Raman, UV–visible and fluorescence spectroscopy, SEM, EDX, XPS, TEM, and TGA analyses. Spectroscopic results confirmed perylene incorporation and imide-linked network formation, while optical studies revealed characteristic perylene-based absorption/emission features and aggregation-related photophysical behavior. Electrochemical measurements showed that polymer architecture strongly influences charge-storage behavior. PEI-3 exhibited higher specific capacitance and better capacitance retention than PEI-5, retaining approximately 83% of its initial capacitance after 3000 charge–discharge cycles, whereas PEI-5 showed lower capacitance but a more compact network architecture and enhanced thermal robustness. A PEI-3 symmetric supercapacitor device further delivered a specific capacitance of 107 F g⁻¹ at 1 A g⁻¹, a maximum energy density of 43 Wh kg⁻¹ at a power density of 850.7 W kg⁻¹, and 81% capacitance retention after 4000 cycles. These findings establish perylene dianhydride cross-linking as a promising route to metal-free, redox-active organic electrode materials for advanced supercapacitors.