Nonlinear Investigation of Fluorene-Benzothiadiazole Copolymers with Multiphoton Absorption and Highlights as Optical Limiters

In recent years, conjugated polymers have garnered significant interest due to their versatile optical and electronic properties, including low band gaps and strong absorption in the visible and near-infrared regions. These features, combined with high molar absorptivity and notable photoluminescence and electroluminescence quantum yields, make these materials highly suitable for applications in optoelectronics, nonlinear optics, and other advanced photonic technologies. This study investigates the linear and nonlinear optical properties of three fluorene-benzothiadiazole-based copolymers-<b>PFDTBT</b>, <b>PFDTBT-M24</b>, and <b>F8BT</b>-differentiated by their electron-accepting units and polymer chain lengths. Through comprehensive spectroscopic analysis, including one-photon absorption, fluorescence emission, and multiphoton absorption studies, as well as quantum chemical calculations, the research provides insights into how molecular design can be optimized for nonlinear optical performance. The results reveal significant two-photon absorption cross sections and demonstrate the potential of these materials for multiphoton-excited fluorescence and optical limiting applications.