Integrating Rigidity and Regular Packing in Ag6 Clusters via Ligand Fluorination: Toward High-Efficiency Low-Loss Optical Waveguiding.

Ligand fluorination offers an effective approach to regulate both molecular packing and excited-state properties in metal nanoclusters for optical waveguiding. In this study, a series of Ag6L6 clusters, Ag6(PPT)6, Ag6(FPPT)6, and Ag6(2FPPT)6, were constructed using stepwise fluorinated ligands. All three clusters feature a slightly distorted octahedral Ag6 core, while fluorination reorganizes intercluster interactions through C─H···F contacts, leading to more regular and compact crystal packing with enhanced lattice rigidity. Photophysical studies reveal that fluorination modulates the emission properties and increases the photoluminescence quantum yield from 35.66% to 98.67%. Theoretical simulations elucidate that fluorination localizes the lowest charge-transfer excited states, simplifies the composition of excited states, and shifts the emissive states from greater metal-centered character toward increased ligand participation, thereby favoring radiative decay and suppressing excited-state absorption. Consequently, both absorption- and scattering-related losses are effectively suppressed, resulting in a substantial decrease in optical loss coefficients from 0.04164 to 0.00365 dB µm-1. Ligand fluorination emerges as a robust approach to achieving organized molecular packing, bolstered lattice rigidity, and refined excited-state configurations, paving the way for high-efficiency, low-loss cluster-based optical waveguides.