Mechanically Triggered Fluorescence/Phosphorescence Switching in the Excimers of Planar Trinuclear Copper(I) Pyrazolate Complexes

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• 作者：Qiong Xiao ; Ji Zheng ; Mian Li ; Shun-Ze Zhan ; Jun-Hao Wang ; Dan Li
• 刊名：Inorganic Chemistry
• 出版年：2014
• 出版时间：November 3, 2014
• 年：2014
• 卷：53
• 期：21
• 页码：11604-11615
• 全文大小：845K
• ISSN：1520-510X

文摘

Luminescence mechanochromism of the well-known Cu₃Pz₃-type (Pz = pyrazolate) complexes is reported here, which is unusual for this family. Two types of new Cu₃Pz₃ complexes, namely Cu₃(EBPz)₃ (1; EBPz = ethyl-4鈥?benzoate-3,5-dimethylpyrazolate) and Cu₃(MBPz)₃ (polymorphs 2a鈥?b>c; MBPz = methyl-4鈥?benzoate-3,5-dimethylpyrazolate), have been synthesized and characterized. Their crystal structures exhibit a similar chairlike dimer stacking supported by short Cu路路路Cu contacts, which would facilitate the formation of photoinduced excimers. The dual emission from the organic fluorophore and excimeric copper cluster phosphor is found to undergo mechanically induced intensity switching between their high-energy (HE) and low-energy (LE) bands. Specifically, the relative intensities of crystalline samples are HE > LE, while the ground solid samples show LE > HE, resulting in the overall emission color interchanging between bluish violet and red. This switching can be reversed by application of solvent to the ground samples, presumably due to recrystallization, and also by heating. TD-DFT calculations reveal that the emissive singlet ligand localized state (S₁) and triplet cluster centered state (T₈) lie close in energy (separated by a gap of 0.1788 eV), suggesting the feasibility of dual emission and the possibility of reverse intersystem crossing, consistent with the long fluorescent lifetimes (10² ns scale) of the HE bands.