Octasubstituted Metal-Free Phthalocyanine as Core of Phosphorus Dendrimers: A Probe for the Properties of the Internal Structure

The synthesis of a new family of phosphorus dendrimers built from an octasubstituted metal-free phthalocyanine core is described up to generation 5. This core is used as a sensor and a probe for
analyzing the properties of the internal structure and the influence of each structural part (core, branches,
surface) upon the whole structure. UV−visible spectra show both a hyperchromic and bathochromic effect
on the Q-bands with increasing generation, indicating that the chromophore is more isolated, and that the
dendritic shell mimics a highly polar solvent. There is no evidence for aggregation, except for generation
0, showing again the isolation of the core. However, the dendritic shell is permeable to aqueous acids and
bases, as demonstrated by the reversible splitting of the Q-band in an acidic medium (neutral form of the
phthalocyanine) and the single Q-band in a basic medium (dianionic form), even for generation 4. The
fluorescence quantum yield for the neutral form increases with increasing generation. The dianionic form
of generation 0 is poorly fluorescent, whereas generations 3 and 4 (G3 and G4) exhibit better fluorescence.
The cores of G3 and G4 are highly sensitive optical sensors for H3O+ and OH-. These experiments are
carried out in THF/water mixtures, and the influence of water on the structure has been checked. The
hydrodynamic radius of generation 4 is measured by NMR diffusion (pulse gradient spin−echo) experiments.
RH varies from 35.4 Å at 4 mol % of water to 32.5 Å at 64 mol % of water in THF, indicating the hydrophobic
nature of these dendrimers.

本文报道了以八取代无金属酞菁为核的新型磷树枝状大分子（phosphorus dendrimers）家族的合成，其合成代数可达第5代。该核被用作传感器与探针，用于分析其内部结构特性，以及各结构组分（核、支化单元、表面）对整体结构的影响。紫外-可见光谱（UV−visible spectra）显示，随着代数增加，Q带同时出现增色效应与红移效应，表明生色团被进一步孤立，且树枝状外壳模拟了高极性溶剂环境。除第0代外，未观察到聚集现象，再次印证了核的孤立性。然而，树枝状外壳可透过水性酸碱：在酸性介质中Q带可逆分裂为酞菁的中性形式，碱性介质中则呈现单Q带（二阴离子形式），这一现象在第4代样品中依然成立。中性形式的荧光量子产率随代数增加而升高。第0代二阴离子形式的荧光强度较弱，而第3、4代（G3、G4）则表现出更优的荧光性能。G3与G4的核可作为H₃O⁺与OH⁻的高灵敏度光学传感器。所有实验均在四氢呋喃（THF）/水混合溶剂中开展，且已验证了水含量对结构的影响。通过核磁共振扩散（脉冲梯度自旋回波，pulse gradient spin−echo）实验测定了第4代样品的流体动力学半径：在四氢呋喃中，当水含量为4 mol%时，流体动力学半径R_H为35.4 Å，当水含量升至64 mol%时，R_H降至32.5 Å，这表明此类树枝状大分子具有疏水特性。