Department of Chemistry, University of Rochester, Rochester, New York 14627, United States.
J Am Chem Soc. 2011 Jan 19;133(2):350-64. doi: 10.1021/ja1070366. Epub 2010 Dec 22.
The dyads 3, 4, and 6, combining the Bodipy chromophore with a Pt(bpy)(bdt) (bpy = 2,2'-bipyridine, bdt = 1,2-benzenedithiolate, 3 and 6) or a Pt(bpy)(mnt) (mnt = maleonitriledithiolate, 4) moiety, have been synthesized and studied by UV-vis steady-state absorption, transient absorption, and emission spectroscopies and cyclic voltammetry. Comparison of the absorption spectra and cyclic voltammograms of dyads 3, 4, and 6 and those of their model compounds 1a, 2, 5, and 7 shows that the spectroscopic and electrochemical properties of the dyads are essentially the sum of their constituent chromophores, indicating negligible interaction of the constituent chromophores in the ground state. However, emission studies on 3 and 6 show a complete absence of both Bodipy-based fluorescence and the characteristic luminescence of the Pt(bpy)(bdt) unit. Dyad 4 shows a weak Pt(mnt)-based emission. Transient absorption studies show that excitation of the dyads into the Bodipy-based (1)ππ* excited state is followed by singlet energy transfer (SEnT) to the Pt(dithiolate)-based (1)MMLL'CT (mixed metal-ligand to ligand charge transfer) excited state (τ(SEnT)(3) = 0.6 ps, τ(SEnT)(4) = 0.5 ps, and τ(SEnT)(6) = 1.6 ps), which undergoes rapid intersystem crossing to the (3)MMLL'CT state due to the heavy Pt(II) ion. The (3)MMLL'CT state is then depopulated by triplet energy transfer (TEnT) to the low-lying Bodipy-based (3)ππ* excited state (τ(SEnT)(3) = 8.2 ps, τ(SEnT)(4) = 5 ps, and τ(SEnT)(6) = 160 ps). The transition assignments are supported by TD-DFT calculations. Both energy-transfer processes are shown to proceed via a Dexter electron exchange mechanism. The much longer time constants for dyad 6 relative to 3 are attributed to the significantly poorer coupling and resonance of charge-separated species that are intermediates in the electron exchange process.
已经合成并通过紫外-可见稳态吸收、瞬态吸收和发射光谱以及循环伏安法研究了二聚体 3、4 和 6，它们将 Bodipy 发色团与 Pt(bpy)(bdt)（bpy = 2,2'-联吡啶，bdt = 1,2-苯二硫醇，3 和 6）或 Pt(bpy)(mnt)（mnt = 丙二腈二硫醇，4）部分结合。比较二聚体 3、4 和 6 的吸收光谱和循环伏安图以及它们的模型化合物 1a、2、5 和 7 的吸收光谱和循环伏安图表明，二聚体的光谱和电化学性质基本上是其组成发色团的总和，表明在基态下组成发色团之间几乎没有相互作用。然而，对 3 和 6 的发射研究表明，既不存在 Bodipy 基荧光，也不存在 Pt(bpy)(bdt)单元的特征发光。二聚体 4 显示出微弱的 Pt(mnt)基发射。瞬态吸收研究表明，激发二聚体进入 Bodipy 基（1）ππ激发态后，会发生单重态能量转移（SEnT）到 Pt（二硫醇）基（1）MMLL'CT（混合金属-配体到配体电荷转移）激发态（τ（SEnT）（3）= 0.6 ps，τ（SEnT）（4）= 0.5 ps，τ（SEnT）（6）= 1.6 ps），由于重 Pt(II) 离子，它迅速经历系间窜越到（3）MMLL'CT 态。（3）MMLL'CT 态然后通过三重态能量转移（TEnT）到低能 Bodipy 基（3）ππ激发态（τ（SEnT）（3）= 8.2 ps，τ（SEnT）（4）= 5 ps，τ（SEnT）（6）= 160 ps）失活。过渡分配得到 TD-DFT 计算的支持。两种能量转移过程都被证明是通过 Dexter 电子交换机制进行的。二聚体 6 的时间常数相对于 3 长得多归因于电子交换过程中中间电荷分离物种的耦合和共振明显较差。
