Hofbeck Thomas, Lam Yan Choi, Kalbáč Martin, Záliš Stanislav, Vlček Antonín, Yersin Hartmut
Institut für Physikalische und Theoretische Chemie, Universität Regensburg , Universitätstrasse 31, D-93040 Regensburg, Germany.
Beckman Institute, California Institute of Technology , Pasadena, California 91125, United States.
Inorg Chem. 2016 Mar 7;55(5):2441-9. doi: 10.1021/acs.inorgchem.5b02839. Epub 2016 Feb 24.
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 (5dz(2)-6pz) excitations, i.e., the singlet state S1 (of (1)A2u symmetry in D4h) and the lowest triplet T1, which splits into spin-orbit substates A1u((3)A2u) and Eu((3)A2u). 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 Eu and A1u. 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).
在1.3 - 310 K的宽温度范围内，研究了高分辨率荧光、磷光以及相关的激发光谱，特别是固体[Bu4N]4[Pt2(μ - P2O5(BF2)2)4]（简称Pt(pop - BF2)）的发射衰减行为。我们关注由dσ*pσ(5dz(2) - 6pz)激发产生的最低激发态，即单重态S1（在D4h中具有(1)A2u对称性）和最低三重态T1，T1分裂为自旋 - 轨道亚态A1u((3)A2u)和Eu((3)A2u)。光激发后，观察到异常缓慢地系间窜越（ISC）。因此，该化合物在研究的温度范围内表现出高效双重发射，由蓝色荧光和绿色磷光组成，总发射量子产率约为100%。我们的研究揭示了这种非凡的双重发射行为，这对于重原子过渡金属化合物来说是独特的。由于自旋、对称性和弗兰克 - 康登重叠限制，Pt(pop - BF2)中的直接ISC过程在很大程度上是禁阻的，因此，对于T < 100 K，ISC时间长达29 ns。随着温度升高，分别通过自旋 - 振动和振动机制促进了两条不同的热激活途径，尽管仍然相对较慢。因此，ISC过程呈现出明显的温度依赖性，荧光/磷光强度比也随之呈现温度依赖性。磷光寿命也与温度有关，反映了三重态T1亚态Eu和A1u的相对布居。高分辨率磷光在10 K以下显示出约220 cm(-1)的红移，这归因于40 cm(-1)的零场分裂加上180 cm(-1)的促进振动。
