A detailed investigation of light-harvesting efficiency of blue color emitting divergent iridium dendrimers with peripheral phenylcarbazole units
作者:Yang-Jin Cho、Kyung-Ryang Wee、Ho-Jin Son、Dae Won Cho、Sang Ook Kang
DOI:10.1039/c3cp53797h
日期:——
The increase in phosphorescence efficiency was estimated by the energy transfer mechanism for divergent iridium dendrimers with peripheral phenylcarbazole units. A series of Ir-core/phenylcarbazole-end dendrons of the type, Ir(dfppy)2(pic-Czn) (Gn, n = 0, 1, 2, and 3), was synthesized, where dfppy, pic, and Czn (n = 2, 4, and 8) are 2-(4,6-difluorophenyl)pyridine, picolinate substituted with Czn at the 3-position, and 4-(9-carbazolyl)phenyldendrons connected with 3,5-di(methyleneoxy)benzyloxy branches, respectively. Selective excitation of the Czn units of G1–G3 resulted in >90% quenching of the Cz fluorescence accompanied by the growth of phosphorescence from the Ir(dfppy)2(pic) core as a consequence of energy transfer from the excited-singlet Czn chromophore to the core. The rate constants of energy transfer were determined by steady-state and transient spectroscopic measurements to be 4.32 × 109 s−1 (G1), 2.37 × 109 s−1 (G2), and 1.46 × 109 s−1 (G3), which were in good agreement with those calculated using the Förster model. The phosphorescence enhancements were 157 (G1), 213 (G2), and 264% (G3) when compared to the phosphorescence of the core Ir(dfppy)2(pic-Ph2) (G0), in which pic-Ph2 is 3-(3,5-dibenzyloxybenzyl)picolinate.
通过具有外围咔唑苯基单元的发散性铱树枝状分子的能量转移机制,估算了磷光效率的增加。合成了一系列Ir核心/咔唑苯端树枝状分子类型,分别为Ir(dfppy)2(pic-Czn) (Gn, n = 0, 1, 2, 3),其中dfppy、pic和Czn (n = 2, 4, 8)依次为2-(4,6-二氟苯基)吡啶、在3-位以Czn取代的吡啶酸,以及连接有3,5-二(甲基亚甲氧基)苯甲氧基分支的4-(9-咔唑基)苯基树枝状分子。选择性激发G1-G3的Czn单元,导致Cz荧光超过90%淬灭,同时伴随着从激发单重态的Czn生色团向核心能量的转移,铱(dfppy)2(pic)核心的磷光增强。通过稳态和瞬态光谱测量确定的能量传递速率常数分别为4.32 × 109 s−1 (G1),2.37 × 109 s−1 (G2) 和 1.46 × 109 s−1 (G3),这与使用Förster模型计算的结果非常吻合。与核心Ir(dfppy)2(pic-Ph2) (G0)的磷光相比,磷光增强分别为157% (G1),213% (G2) 和 264% (G3),其中pic-Ph2是3-(3,5-二苯基氧基苯甲基)吡啶酸。