Departamento de Química, Facultad de Ciencias Exactas Físico Químicas y Naturales, Universidad Nacional de Río Cuarto, Río Cuarto, Argentina.
Photochem Photobiol. 2018 Nov;94(6):1129-1137. doi: 10.1111/php.13033. Epub 2018 Nov 7.
The photophysical and photochemical properties of the xanthene dyes mercurochrome (MCr) and eosin-Y (Eos); and the phenazine dye safranine-O (SF) are evaluated in the presence of amino-terminated polyamidoamine (PAMAM) dendrimers of low generations. The dendrimers produce a red shift in the UV-vis absorption spectra of the dyes, which increases with concentration and the size of the PAMAM molecule. The Stern-Volmer plots of fluorescence quenching for xanthenic dyes present a downward curvature. It is ascribed to a static mechanism involving a dye-dendrimer binding. A non-linear fitting of the SV plots allows the calculation of the binding constants. For SF, the fluorescence is only slightly quenched by PAMAMs and the SV plots are linear. The binding constants are in the order K (SF) ≪ K (Eos) < K (MCr). The difference must be due to important specific structural effects. A decrease in the triplet lifetime and an increase in the absorption of the semireduced form of the dyes are observed in the presence of dendrimers. While for the two xanthene dyes, the rate constants reach the diffusional limit for G2 and G3, for SF they are one order of magnitude lower. This is explained by a different quenching mechanism of the two types of dyes.
研究了吖啶染料汞铬菁（MCr）和曙红 Y（Eos）以及吩嗪染料碱性藏红 T（SF）在低代数的端氨基聚酰胺-胺（PAMAM）树状大分子存在下的光物理和光化学性质。树状大分子使染料的紫外-可见吸收光谱发生红移，这种红移随浓度和 PAMAM 分子的大小而增加。吖啶染料的荧光猝灭的 Stern-Volmer 图呈现出向下的弯曲。这归因于涉及染料-树状大分子结合的静态机制。SV 图的非线性拟合允许计算结合常数。对于 SF，PAMAMs 对 SF 的荧光猝灭作用很小，SV 图是线性的。结合常数的顺序为 K（SF）≪K（Eos）<K（MCr）。这种差异一定是由于重要的特定结构效应。在树状大分子存在下，观察到染料的三重态寿命降低和半还原形式的吸收增加。对于两种吖啶染料，G2 和 G3 的速率常数达到扩散限制，而对于 SF，它们低一个数量级。这可以通过两种类型的染料的不同猝灭机制来解释。
