Thermally Tunable Dual Emission of the d8–d8 Dimer [Pt2(μ-P2O5(BF2)2)4]4‿/sup>

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• 作者：Thomas Hofbeck ; Yan Choi Lam ; Martin Kalbáč ; Stanislav Záliš ; Antonín Vlček Jr. ; Hartmut Yersin
• 刊名：Inorganic Chemistry
• 出版年：2016
• 出版时间：March 7, 2016
• 年：2016
• 卷：55
• 期：5
• 页码：2441-2449
• 全文大小：553K
• ISSN：1520-510X

文摘

High-resolution fluorescence, phosphorescence, as well as related excitation spectra, and, in particular, the emission decay behavior of solid [Bu₄N]₄[Pt₂(μ-P₂O₅(BF₂)₂)₄], abbreviated Pt(pop-BF₂), have been investigated over a wide temperature range, 1.3–310 K. We focus on the lowest excited states that result from dσ*pσ (5d_z²–6p_z) excitations, i.e., the singlet state S₁ (of ¹A_2u symmetry in D_4h) and the lowest triplet T₁, which splits into spin–orbit substates A_1u(³A_2u) and E_u(³A_2u). After optical excitation, an unusually slow intersystem crossing (ISC) is observed. As a consequence, the compound shows efficient dual emission, consisting of blue fluorescence and green phosphorescence with an overall emission quantum yield of ∼100% over the investigated temperature range. Our investigation sheds light on this extraordinary dual emission behavior, which is unique for a heavy-atom transition metal compound. Direct ISC processes in Pt(pop-BF₂) are largely forbidden due to spin-, symmetry-, and Franck–Condon overlap-restrictions and, therefore, the ISC time is as long as 29 ns for T < 100 K. With temperature increase, two different thermally activated pathways, albeit still relatively slow, are promoted by spin-vibronic and vibronic mechanisms, respectively. Thus, distinct temperature dependence of the ISC processes results and, as a consequence, also of the fluorescence/phosphorescence intensity ratio. The phosphorescence lifetime also is temperature-dependent, reflecting the relative population of the triplet T₁ substates E_u and A_1u. The highly resolved phosphorescence shows a ∼220 cm^–1 red shift below 10 K, attributable to zero-field splitting of 40 cm^–1 plus a promoting vibration of 180 cm^–1.