Two Bodipy-based chromophores have been synthesized, which bear two methoxyphenyl substituents in the 1,7 positions and either hydrogen (L1) or bromine (L2) atoms in the 2,6 positions, with the aim of testing their ability to sensitize the luminescence of near-infrared emitting LnIII ions. Despite the presence of the two halogen substituents in L2, the two chromophores display very similar absorption and emission properties, the only difference being a drop in the quantum yield from 31% for L1 to 21% for L2. In addition, no triplet state emission could be evidenced for both chromophores as well as for their tris complexes with GdIII ions. This is traced back to unfavorable conformation of the molecule, preventing efficient intersystem crossing. Complexes with stoichiometry [Ln(Li)3(tpy)] have been isolated for Ln = Gd, Er, Yb and fully characterized. Ligand emission is partially quenched (20–40%) in the ErIII and YbIII complexes and typical metal-centred luminescence is detected at 1530 (ErIII) and 978 (YbIII) nm upon excitation in the orange portion of the visible spectrum (583 nm). In these complexes, the main energy transfer pathway involves the singlet state(s) of the ligands: the lowest 1ππ state emission overlaps the Er(4F9/2 ← 4I15/2) absorption band and the 1ππ–Yb(2F5/2) gap amounts to only 5700 cm−1. This study demonstrates that the Bodipy framework is adequate for sensitizing the luminescence of NIR-emitting lanthanide ions, allowing excitation wavelengths extending into the orange portion of the visible spectrum and yielding complexes with large molar absorption coefficients (log ε ≈ 5.0–5.2). Additionally it also points to the importance of the conformation of the chromophores on the yield of intersystem crossing.
合成了两种基于 Bodipy 的发色团,它们在 1,7 位上带有两个
甲氧基苯基取代基,在 2,6 位上带有氢 (L1) 或
溴 (
L2) 原子,目的是测试它们的发光敏化能力近红外发射 LnIII 离子。尽管
L2 中存在两个卤素取代基,但这两个发色团表现出非常相似的吸收和发射特性,唯一的区别是量子产率从 L1 的 31% 下降到
L2 的 21%。此外,两种发色团及其与 GdIII 离子的 tris 配合物均未证明有三重态发射。这可以追溯到分子的不利构象,从而阻止了有效的系统间交叉。
化学计量 [Ln(Li)3(tpy)] 的配合物已被分离出来,其中 Ln = Gd、Er、Yb 并得到充分表征。 ErIII 和 YbIII 配合物中的
配体发射被部分猝灭 (20–40%),并且在可见光谱 (583 nm) 的橙色部分激发后,在 1530 (ErIII) 和 978 (YbIII) nm 处检测到典型的
金属中心发光。在这些配合物中,主要的能量转移途径涉及
配体的单线态:最低的 1ππ 态发射与 Er(4F9/2 ← 4I15/2) 吸收带和 1ππ–Yb(2F5/2) 间隙重叠仅为 5700 cm−1。这项研究表明,Bodipy 框架足以敏化近红外发射的
镧系元素离子的发光,允许激发波长延伸到可见光谱的橙色部分,并产生具有大摩尔吸收系数的配合物(log ε ≈ 5.0–5.2)。此外,它还指出了发色团的构象对系统间杂交产量的重要性。