Chemical Sciences and Technology Division, National Institute for Interdisciplinary Science and Technology, Thiruvananthapuram-695019, Kerala, India.
J Phys Chem B. 2011 Sep 22;115(37):10789-800. doi: 10.1021/jp204388m. Epub 2011 Aug 29.
Here, we report new carboxylic functionalized poly(phenylene)s and their oligomers as selective and efficient photosensitizers for Eu(3+) ions. Palladium-catalyzed Suzuki polycondensation was developed for the synthesis of carboxylic functionalized π-conjugated materials. The chemical structures of the polymer skeleton were varied using two anchoring groups consisting of ethylhexyloxy and methoxy substitution in the chain backbone. The molecular weights of the polymer samples were obtained in the range of 4000-8000 containing 20 aromatic units in the chain. Photoexcitation of the oligomer-Eu(3+) complexes resulted in magenta color emission as a result of the combination of partial blue self-emission from the chromophores along with the red color from the metal center. The ethylhexyl substituted polymer-Eu(3+) complex showed complete excitation energy transfer from the macromolecular chains to the metal center and produced bright and sharp red emission. The polymer-containing methoxy unit was found to show largely self-emission rather than photoexcitation to the metal center. Singlet and triplet energy levels of the complexes and chromophores revealed that both oligomers and polymers have almost identical energy levels for photosensitizing Eu(3+) ions. The polymers possessed typical amphiphilic structures via a rigid aromatic hydrophobic core and hydrophilic anionic periphery for self-organization in water. Both dynamic light scattering and atomic force microscope analysis confirmed the existence of the spherical shape nanometer size aggregates of the polymer chains in water. The branched ethylhexyl polymer showed the formation of loosely packed 500 nm aggregates whereas tightly packed 200 nm particles are produced by the methoxy substituted rigid polymer. These molecular aggregates behaved as templates for complexation as well as photosensitizing of the Eu(3+) ions. The loosely packed nanoaggregates (ethylhexyl polymer) contain Eu(3+) ions in the entire scaffold and showed efficient and complete energy transfer from the conjugated chain to metal ions. The tightly packed rigid-chains in methoxy polymer restricted the complete energy transfer to metal center. The molecular self-organization of the polymers played a crucial role on the efficient energy transfer from the polymer chain to metal center, more specifically Eu(3+) ion-based red emission.
在这里，我们报告了新的羧酸官能化聚（亚苯基）及其低聚物，它们是 Eu(3+) 离子的选择性和高效光敏剂。钯催化的 Suzuki 缩聚被开发用于合成羧酸官能化的 π 共轭材料。通过在链骨架中使用两种锚定基团，即乙基己氧基和甲氧基取代，来改变聚合物骨架的化学结构。聚合物样品的分子量在 4000-8000 范围内，链中含有 20 个芳基单元。低聚物-Eu(3+) 配合物的光激发导致由于发色团的部分蓝色自发射与金属中心的红色结合而产生洋红色发射。乙基己基取代的聚合物-Eu(3+) 配合物表现出从高分子链到金属中心的完全激发能量转移，并产生明亮而尖锐的红色发射。含甲氧基单元的聚合物被发现主要表现出自发射而不是对金属中心的光激发。配合物和发色团的单重态和三重态能级表明，低聚物和聚合物都具有几乎相同的能级来敏化 Eu(3+) 离子。聚合物通过刚性芳环疏水性核和亲水性阴离子外围具有典型的两亲性结构，可在水中自组装。动态光散射和原子力显微镜分析均证实了聚合物链在水中形成球形纳米尺寸聚集体的存在。支化的乙基己基聚合物形成松散堆积的 500nm 聚集体，而甲氧基取代的刚性聚合物则形成紧密堆积的 200nm 颗粒。这些分子聚集体既可以作为配合物的模板，也可以作为 Eu(3+) 离子的光敏剂。松散堆积的纳米聚集体（乙基己基聚合物）在整个支架中包含 Eu(3+) 离子，并表现出从共轭链到金属离子的有效和完全能量转移。甲氧基聚合物中刚性链的紧密堆积限制了能量向金属中心的完全转移。聚合物的分子自组织在从聚合物链到金属中心的有效能量转移中起着关键作用，更具体地说，是基于 Eu(3+) 离子的红色发射。
