End Group-Induced Ultrafast Exciton Dissociation of Supramolecular Perylene Monoimide Nanoribbons for Efficient Photocatalytic Hydrogen Evolution

Achieving fast exciton dissociation is a critical factor for optimizing the performance of organic photocatalysts in solar energy conversion. This work demonstrates the end-group-dependent ultrafast exciton dissociation in supramolecular perylene monoimide (PMI) nanostructures. A series of PMI molecules are designed by connecting the amide site with methylene carboxyl (─CH₂─COOH), methylene phosphonic acid (─CH₂─PO₃H₂), and methylene sulfonic acid (─CH₂─SO₃H) to increase the dipole moment and built-in electric field, thereby effectively diminishing exciton binding energy. Upon photoexcitation, self-assembled PMI-CH₂-SO₃H nanoribbons (NRs), which exhibit the lowest exciton binding energy of 29.4 meV, achieve ultrafast exciton dissociation within 0.25 ps, leading to the formation of charge-separated excitons from charge-transfer states. This dissociation rate is ≈40 and 16 times faster than that observed in PMI-CH₂-COOH (NRs) and PMI-CH₂-PO₃H₂ (NRs), respectively. Following the deposition of Pt nanoparticles on PMI NRs, Pt/PMI-CH₂-SO₃H (NRs) demonstrates an H₂ evolution of 21.2 mmol g⁻¹ h⁻¹ under visible light irradiation (λ > 420 nm), outperforming Pt/PMI-CH₂-COOH (NRs) and Pt/PMI-CH₂-PO₃H₂ (NRs) by factors of 53 and 5.4, respectively.