Quinolone-functionalized glycine dipeptides: TPA enhancement and charge transfer mechanism

To develop efficient unnatural amino acid two photon absorption (TPA) materials, the structure of experimental molecule N-(3-(2,3-diphenylquinoxaline-6-ylo)alanylo) glycine (DQA) was modified by introducing electron-rich groups and extending the delocalization range of π electrons within the side chain. The influence of the functional side chain on the optical properties and TPA performance of DQA derivatives was systematically explored, and the intrinsic structure-function relationship was further analyzed. Calculations based on density functional theory (DFT) combined with sum over states model demonstrate that extending π-conjugation effectively enhances the TPA cross-section. The introduction of imino and indole groups with strong electron-donating characteristics, significantly enhanced π-electron delocalization within the molecular system, and reduced the electron transition energy gap. As a result, compound DQA3 exhibits a high TPA cross-section of 221,974.8 GM and a large Stokes shift of 355.3 nm, demonstrating broad promising potential application in biological cell imaging.