Modulating the photophysical properties of perylene-based light-harvesting materials via bay-induced distortion and...

The design of light-harvesting materials is fundamentally rooted in controlling the photophysical and photochemical properties. Herein, we investigate bay-functionalized light harvesting perylenediimides (PDIs) by applying this principle to atomistically defined perylene-based nanographene molecular models. Our approach combines computational modeling (CAM-B3LYP-D3) with a suite of experimental techniques, including steady-state UV-vis absorption, steady-state and time-resolved emission, and electrochemical analysis. The synergistic combination of bay-induced twisting and electron donation is predicted to preferentially destabilize the Highest Occupied Molecular Orbital (HOMO) relative to the Lowest Unoccupied Molecular Orbital (LUMO), activating partial Charge Transfer (CT) character in the primary electronic transition (predominantly HOMO → LUMO). This is visually confirmed by Electron Density Difference (EDD) maps and supported by a calculated increase in dipole moment magnitude (Δµ) vertically and more so adiabatically. This electronic modulation results in a bathochromic shift which can exceed 150 nm in electron-rich derivatives such as PDI-(Py)₂. In contrast, electron-poor PDI-(CN)₂ exhibits little to no shift, while the planar, benzimidazole-fused PDI-Imd shows relative HOMO stabilization, leading to a wider HOMO-LUMO gap and displays a notable experimental hypsochromic shift. Ultimately, this work aims to clarify the structure-property relationships of these compounds. By computationally validating how specific structural distortions (twisting) and electronic substituents dictate absorption and emission, we nominate these tailored scaffolds for light-harvesting applications. These insights help uncover the mechanistic rules governing their photophysics, serving as a practical springboard for future studies in perylene-based nanographenes.