Exploring the Role of Squaraine Infusion on Two-Photon Absorption Cross-Section of a few Functionalized BODIPY like Systems

Abstract

In the current work, we considered two fusion frameworks of BODIPY-Squaraine (bdp-sq) systems and functionalized them with selected polar groups (-X; -enX where en=ethenyl; X = NMe₂, PY₅, and PY₆). Utilizing state-of-the-art quadratic response theory (RI-CC2), we systematically examined how these fusion strategies and polar substitutions modulate their optical properties. Our findings indicate that these structural modifications effectively tune both the linear and nonlinear optical properties. Notably, a substantial enhancement in two-photon absorption (TPA) strengths was observed across all investigated systems, with those featuring extended conjugation lengths exhibiting markedly higher TPA efficiencies. Certain systems exhibited strong TPA responses in the near-infrared region (∼ 1200nm), rendering them to be promising candidates for several nonlinear optical applications. To gain deeper insight into the key factors influencing TPA strengths, we further employed a generalized few-state model to analyze the dominant transition dipole moments and their relative orientations in the most TP-active systems from each fusion scheme. Our investigation contributes a useful starting point for further exploration of these kinds of fused bdp-sq systems that can be TP active and also provides a valuable foundation for future experimental research and development.