Nonlinear Optical Properties in V-Shaped Fluorenones: A Charge-Transfer Mechanism Regulated by Molecular Self-Assembly

Nonlinear optical (NLO) materials play a vital role in the field of optical communication. Among these, V-shaped fluorenone molecules are of particular importance in the development of all-carbon polymers, as their self-assembled supramolecular structures exhibit excellent NLO properties. In this study, density functional theory (DFT) was employed to investigate the structures, molecular orbitals, absorption spectra, and nonlinear optical responses of DPFO monomers, dimers, and trimers. The results showed that as self-assembly progressed and the number of molecular layers increased, the band gap energy (E gap ) gradually decreased. Concurrently, with increasing aggregation, the absorption peaks showed redshift, accompanied by enhanced absorption intensity. Moreover, the polarizability (𝛼 tot ), first hyperpolarizability (𝛽 tot ), and second hyperpolarizability (𝛾 tot ) of the V-shaped fluorenone molecules increased significantly with the degree of aggregation. Specifically, the trimer exhibited values as high as 1411.9 a.u., 702.5 a.u., and 1,988,797 a.u. for 𝛼 tot , 𝛽 tot , and 𝛾 tot , respectively. These findings demonstrated that enhancing the degree of aggregation was an effective strategy for boosting the NLO response. This work provided a theoretical foundation for further experimental research on the self-assembly behavior and nonlinear optical properties of V-shaped fluorenone molecules.