Efficient separation of photo-generated carriers for in-situ induction of PDI cation radicals to enhance the photocatalytic performance of PDI supramolecules

In order to investigate whether the formation of hydrogen bonds can affect the degradation products of pollutants, a photocatalyst PDI-SE was obtained by end substituting perylene tetracarboxylic dianhydride with serine (SE) in this paper. As a reference, PDI-IS with isopropylamine (IS) terminal alkyl substitution was synthesized simultaneously. Their photocatalytic performance to decompose phenol and tetrabromobisphenol A (TBBPA) were investigated. PDI-SE could degrade 79.3% of phenol or 68.4% of TBBPA within 4 hours under visible light. The degradation products of TBBPA were tracked using high-resolution mass spectrometry. The morphology, composition, structure, and optoelectronic properties of two photocatalysts, particularly their transient absorption spectra and fluorescence lifetime were studied. We also conducted theoretical calculations on their binding energy with phenol or TBBPA, distribution and separation of electron and hole of excited state PDI-SE and PDI-IS supramolecules. Due to the formation of hydrogen bonds the binding energy of PDI-SE with phenol or TBBPA is 1.24 eV or 1.99 eV, which is stronger than that of PDI-IS (0.85 eV or 1.66 eV). Although both PDI-SE and PDI-IS can form free radical cations in excited states, the high separation of electrons and holes of PDI-SE leads to a longer lifetime of free radical cations, so caused its excellent photocatalytic activity compared to PDI-IS. This article proposes a new strategy based on molecular design to promote efficient separation of photogenerated electrons and holes, thereby forming stronger oxidizing PDI cationic radicals in situ to enhance the photocatalytic performance of PDI supramolecules.