Modulating Two‐Photon Absorption in a Pyrene‐Based MOF Series: An In‐Depth Investigation of Structure–Property Relationships

Metal-organic frameworks (MOFs) are emerging as promising materials for multiphoton absorption (MPA), a nonlinear optical phenomenon relevant for applications, such as bioimaging, phototherapy, and photonic devices. However, the structural features that govern their exceptional MPA activity remain poorly understood. To address this, a family of pyrene-based MOFs (NU-1000, NU-901, SrTBAPy, and BaTBAPy), that vary in topology and secondary building units (SBUs), is systematically investigated. Significant differences are observed in the two-photon absorption (2PA) cross-section sigma (2), with BaTBAPy exhibiting the highest activity (8.2 x 104 GM). Quantum mechanical calculations reveal that intermolecular chromophore interactions and SBU-induced effects contribute strongly to enhanced sigma (2) values, particularly in NU-901 and BaTBAPy. The findings demonstrate that both framework topology and metal coordination environments are critical to modulating MPA behavior. These insights into the structure-property relationships of MOFs pave the way for rational design of next-generation nonlinear optical materials.