Substituent-controlled electronic redistribution and nonlinear optical response across the Ag-S interface in W@Ag12 -BDT hybrids: a DFT/TD-DFT study.

CONTEXT: Atomically precise silver nanoclusters provide well-defined inorganic platforms for molecular modeling of cluster-π interactions, but the relationships among terminal substitution, electronic redistribution across an Ag-S anchoring environment, and molecular nonlinear optical response remain insufficiently understood. Herein, W@Ag12-BDT-X hybrids, where BDT denotes benzo[1,2-b:4,5-b']dithiophene and X = H, CH3, NH2, SCH3, NO2, CN, and CF3, are examined as a structurally comparable molecular series. The optimized complexes retain the W-centered Ag12 framework, while the selected structural parameters show only limited variation, with W-Ag distances ranging from approximately 2.70 to 2.73 Å, an Ag-Sanchor distance of approximately 2.53 Å, and a neighboring Ag-Ag distance of approximately 2.86 Å. This structural comparability supports interpretation of the observed property trends in relation to substituent-dependent electronic redistribution, while smaller geometric contributions cannot be excluded. Within the investigated series, donor substitution is associated with increased interfacial polarization, whereas acceptor substitution is associated more clearly with LUMO stabilization and increased ligand participation in selected excited states. C-NH2 gives the largest first hyperpolarizability in the series, with βtot values of 7036.3, 8044.8, and 10,849.2 a.u. at 0, -ω, and -2ω, respectively; by contrast, the second hyperpolarizability is more sensitive to frequency, functional choice, and projected tensor contributions. METHODS: Geometry optimization, frequency analysis, frontier-orbital analysis, time-dependent density functional theory (TD-DFT) calculations, and static/dynamic NLO computations were performed using Gaussian 16. The long-range-corrected LC-BLYP functional was employed with aug-cc-pVDZ for non-metal atoms and aug-cc-pVDZ-PP effective-core-potential basis sets for Ag and W atoms. Hole-electron descriptors and orbital contributions were analyzed using Multiwfn, while frontier orbitals, hole-electron distributions, and density-difference maps were visualized using VESTA. Dynamic NLO responses were evaluated at 1064 nm.