A molecular clip throws new light on the complexes formed by a family of cyclam-cored dendrimers with Zn(<scp>ii</scp>) ions. Efficient energy transfer in the heteroleptic complexes
作者:Barbara Branchi、Giacomo Bergamini、Luca Fiandro、Paola Ceroni、Antonello Alvino、Giancarlo Doddi、Fritz Vögtle、Frank-Gerrit Klärner
DOI:10.1039/c0dt01202e
日期:——
Complexation of Zn(II) ions by cyclam cored dendrimers appended with four (G0), eight (G1) and 16 naphthyl chromophores (G2) at the periphery have been investigated in CH3CN–CH2Cl2 1 : 1 (v/v) solution by absorption and emission, ESI-mass and 1H NMR spectroscopy. The results obtained can be interpreted by the formation of complexes of 2 : 1 dendrimer to metal stoichiometry, at low metal ion concentration, and 1 : 1 complexes upon further addition of Zn(II) ions, for all the dendrimer generations. Upon addition of a molecular clip C2− consisting of two anthracene sidewalls bridged by a benzene group with two sulfate substituents in the para positions, heteroleptic complexes of general formula [GnnZnC] are formed. Interestingly, in these complexes, a very efficient quenching (practically 100%) of the dendrimer naphthyl luminescence and sensitization (ca. 90%) of the clip anthracene emission take place. The complex [G2ZnC] exhibits a very high molar absorption coefficient in the UV spectral region owing to the 16 naphthyl chromophores of the dendrimer and the two anthracene units of the clip (ε = 1.7 × 105 M−1 cm−1 at 263 nm). Furthermore, the excitation energy absorbed by the naphthyl chromophores is efficiently funneled to the two anthracene units of the clip, which emits in the blue spectral region.
通过吸收在 CH3CN–CH2Cl2 1 : 1 (v/v) 溶液中研究了外围附加有 4 个 (G0)、8 个 (G1) 和 16 个萘基发色团 (G2) 的 cyclam 核树枝状聚合物对 Zn(II) 离子的络合和发射、ESI 质量和 1H NMR 光谱。对于所有的树枝状聚合物,所得结果可以通过在低金属离子浓度下形成 2 : 1 树枝状聚合物与金属化学计量的复合物以及进一步添加 Zn(II) 离子后形成 1 : 1 复合物来解释。添加由两个蒽侧壁组成的分子夹 C2−,并通过对位具有两个硫酸盐取代基的苯基团桥接,形成通式 [GnnZnC] 的杂配配合物。有趣的是,在这些配合物中,树枝状聚合物萘基发光发生非常有效的猝灭(几乎 100%),并且夹蒽发射发生敏化(约 90%)。由于树枝状聚合物的 16 个萘基发色团和夹子的两个蒽单元,复合物 [G2ZnC] 在紫外光谱区表现出非常高的摩尔吸收系数(263 nm 处 ε = 1.7 × 105 M−1 cm−1) 。此外,萘基发色团吸收的激发能量有效地集中到夹子的两个蒽单元,在蓝色光谱区域发射。