Functionalisation of PTCDA to PDI derivatives: impact on optical and fundamental bandgap, solubility, and electronic structure

Abstract The transformation of 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) to perylene diimide (PDI) and further derivatives offers a promising strategy to tailor the solubility and electronic properties of organic semiconductors for optoelectronic applications. In this study, a series of PDI derivatives with targeted substituents at the imide and bay positions was synthesised and systematically characterised. Structural integrity and functionalisation were confirmed by solid-state NMR, FTIR, and XPS. Solubility measurements revealed that branched alkyl or cyclohexyl groups at the imide position significantly enhance solubility, while diamide polyether chains can induce crosslinking and reduce processability. UV/Vis-spectroscopy, Ultraviolet Photoelectron Spectroscopy (UPS), and Reflection Electron Energy Loss Spectroscopy (REELS) were used to determine optical and fundamental bandgaps as well as HOMO levels. Electron-donating substituents at the imide position increased the HOMO level and narrowed the bandgap, whereas electron-withdrawing NO 2 groups at the bay position lowered the HOMO and widened the bandgap. The difference between optical and fundamental bandgaps highlights the significant exciton binding energy in these materials. Overall, this work demonstrates structure–property relationships in PDI derivatives, providing a framework for the rational design of next-generation organic electronic materials with optimised solubility and electronic structure.