Predicting and controlling the second-order NLO response in a new class of multi-decker sandwich clusters {µ-B2H2S2Pd(Cl)2}-(CoCp)n, (n = 2 to 5)
Abstract
Using density functional theory calculations, we have conducted a systematic investigation of the nonlinear optical properties of a series of multi-decker sandwich clusters, [{H2B2S2Pd(Cl)2}-(CoCp)n] (n = 2 to 5), which vary in structural configuration, shape and size namely MDSn, MDSna and MDS’n. The analysis encompassed polarizability, anisotropy of polarizability, and first-order hyperpolarizability, providing detailed insights into their geometric structure, stability, electronic properties, and absorption spectra. A comprehensive evaluation was performed to assess the impact of the {H2B2S2Pd(Cl)2} fragment’s positioning, the number of (CoCp) units, and the incident frequency (ω = 0, 0.0428, 0.034, 0.0239 a.u.) on their first and second-order NLO responses. The results indicate that these clusters exhibit a significant NLO response, which is further amplified under an external electric field. Notably, the first hyperpolarizability (β) of the MDS’n series increases with the number of (CoCp) units (n = 2 to 4). However, a decrease in β is observed when the (CoCp) unit count reaches 5. Conversely, for MDSn (n = 2 to 5), first hyperpolarizability consistently rises with the number of (CoCp) units from n = 2 to 5, reflecting behavior akin to traditional push–pull π-systems. These findings underscore that the design of multi-decker sandwich clusters is a highly effective strategy for enhancing second-order NLO responses, primarily due to efficient charge transfer across the layered structure.
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