Femtosecond Measurements Of Size-Dependent Spin Crossover In FeII(pyz)Pt(CN)4 Nanocrystals

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• 作者：D. M. Sagar ; Frederick G. Baddour ; Patrick Konold ; Joel Ullom ; Daniel A. Ruddy ; Justin C. Johnson ; Ralph Jimenez
• 刊名：The Journal of Physical Chemistry Letters
• 出版年：2016
• 出版时间：January 7, 2016
• 年：2016
• 卷：7
• 期：1
• 页码：148-153
• 全文大小：459K
• ISSN：1948-7185

文摘

We report a femtosecond time-resolved spectroscopic study of size-dependent dynamics in nanocrystals (NCs) of Fe(pyz)Pt(CN)₄. We observe that smaller NCs (123 or 78 nm cross section and <25 nm thickness) exhibit signatures of spin crossover (SCO) with time constants of ～5–10 ps whereas larger NCs with 375 nm cross section and 43 nm thickness exhibit a weaker SCO signature accompanied by strong spectral shifting on a ～20 ps time scale. For the small NCs, the fast dynamics appear to result from thermal promotion of residual low-spin states to high-spin states following nonradiative decay, and the size dependence is postulated to arise from differing high-spin vs low-spin fractions in domains residing in strained surface regions. The SCO is less efficient in larger NCs owing to their larger size and hence lower residual LS/HS fractions. Our results suggest that size-dependent dynamics can be controlled by tuning surface energy in NCs with dimensions below ～25 nm for use in energy harvesting, spin switching, and other applications.