Xiao Qiong, Zheng Ji, Li Mian, Zhan Shun-Ze, Wang Jun-Hao, Li Dan
Department of Chemistry and Key Laboratory for Preparation and Application of Ordered Structural Materials of Guangdong Province, Shantou University , Guangdong 515063, People's Republic of China.
Inorg Chem. 2014 Nov 3;53(21):11604-15. doi: 10.1021/ic5016687. Epub 2014 Oct 22.
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'-benzoate-3,5-dimethylpyrazolate) and Cu3(MBPz)3 (polymorphs 2a-c; MBPz = methyl-4'-benzoate-3,5-dimethylpyrazolate), have been synthesized and characterized. Their crystal structures exhibit a similar chairlike dimer stacking supported by short Cu···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 (10(2) ns scale) of the HE bands.
本文报道了著名的Cu3Pz3型（Pz = 吡唑酸酯）配合物的发光机械变色现象，这在该家族中并不常见。合成并表征了两种新型的Cu3Pz3配合物，即Cu3(EBPz)3（1；EBPz = 4'-苯甲酸乙酯-3,5-二甲基吡唑酸酯）和Cu3(MBPz)3（多晶型物2a - c；MBPz = 4'-苯甲酸甲酯-3,5-二甲基吡唑酸酯）。它们的晶体结构呈现出由短Cu···Cu接触支撑的类似椅状二聚体堆积，这将促进光诱导准分子的形成。发现有机荧光团和准分子铜簇磷光体的双重发射在其高能（HE）和低能（LE）带之间经历机械诱导的强度切换。具体而言，结晶样品的相对强度为HE > LE，而研磨后的固体样品显示LE > HE，导致整体发射颜色在蓝紫色和红色之间互换。通过向研磨后的样品施加溶剂（可能是由于重结晶）以及加热，可以使这种切换逆转。TD-DFT计算表明，发射单重态配体局域态（S1）和三重态簇中心态（T8）的能量相近（相差0.1788 eV），这表明双重发射的可行性以及反向系间窜越的可能性，与HE带的长荧光寿命（10² ns尺度）一致。
