Bay-substituted perylene diimide-based donor–acceptor type copolymers: design, synthesis, optical and energy storage behaviours

Abstract

A series of bay-substituted PDI-based conjugated copolymers, which are composed of a linker as the donor moiety and perylene core as the strong p-electron acceptor moiety, have been designed to investigate the modulation of the photophysical properties with increasing donor–acceptor strength. After successful synthesis, all copolymers (namely, Benz-PDI, Btz-PDI, TzTz-PDI and NH-PDI) have been characterized by ¹³C NMR, MALDI-ToF and FT-IR analyses. The copolymers are moderately stable upon heating and are semi-crystalline in nature (except TzTz-PDI and NH-PDI). The optical characteristics of the copolymers are determined by absorption and emission studies. The redox properties of these copolymers are observed to change with increasing donor–acceptor strength, which is further supported by DFT calculations. Initial electrochemical studies reveal that the designed copolymers have the potential to be used as pseudocapacitive materials for energy storage applications. Among the four copolymers, charge–discharge studies indicate that NH-PDI produces the highest specific capacitance of 363 F g⁻¹ with outstanding cyclic stability of 15 000 cycles under a three-electrode setup. A symmetric supercapacitor device made of NH-PDI produced a specific capacitance of 134.2 F g⁻¹ with relatively higher values of specific energy density (E) and specific power density (P_max) at a current density of 0.5 A g⁻¹. The excellent result of PDI-embedded conjugated donor–acceptor polymers reveals a novel design strategy as well as the subsequent application of a new type of a stable polymeric electrode material for high-performance supercapacitors.