Development of the dendrimer photochemistry and the reaction dynamics

(1)光异构化机理合成交联1,3,5-三苯基苯树状大分子，研究其光化学异构化机理。在辐照下，交联枝状大分子异构化的量子产率为0.063，与模型化合物的量子产率（0.080）相差不大，支持光化学E-Z异构化过程中的体积守恒机制。(2)核心部分光异构化引发的树状大分子整体结构变化。采用时间分辨瞬态光栅法研究了二苯乙烯树状大分子在水中受光激发的构象动力学和能量释放过程。第一代的能量弛豫和构象变化在30ns内完成，而第二代和第三代的动力学变化较慢。(3)提高树状发色团的荧光量子产率研究了一系列新合成的具有2-…More（2′-羟基苯基）-苯并恶唑（HBO）核的树状大分子在苯中的光化学性质。一般来说，HBO及其类似物的荧光量子产率很小，但测定了G0、G2和G3树枝状大分子的荧光量子产率分别为0.022、0.030和0.038，并在更高代的树枝状大分子中增加。(4)提高树状二苯乙烯光激发生成单重态氧的量子产率。由于二苯乙烯核状树状大分子G1-G4的核心部分的激发单重态的寿命约为0.10 ns，氧淬灭了它们的激发单重态，产生了单重态氧。基于二苯乙烯核心淬火的单线态产氧效率在G4二苯乙烯树状聚合物中最高。(5)利用两亲性树突自组装发色团研究了两亲性芘核聚芳醚树状大分子的自组装。在低浓度的KOH水溶液中观察到高代芘准分子的发射。结果表明，在水溶液中，高代树状大分子的自聚集效率高于低代树状大分子。少

(1)Photoisomerization mechanismA cross-linked 1,3,5-tristyrylbenzene dendrimer was synthesized to study the photochemical isomerization mechanism. On irradiation, cross-linked dendrimer isomerized with the quantum yields of 0.063, which was not very much different from that for a model compound (0.080), supporting a volume-conserving mechanism during the photochemical E-Z isomerization.(2)Whole structural change of the dendrimers triggered by photoisomerizaition at the core partThe conformational dynamics and the energy-releasing process of stilbene dendrimers upon photoexcitation in water are investigated by the time-resolved transient grating method. Whereas the energy relaxation and the conformational change are completed within 30 ns for the first generation, slower dynamics are observed for the second and the third generations.(3)Increasing the fluorescence quantum yield in dendronized chromophoreThe photochemical properties of a series of newly synthesized dendrimers, having a 2- … More (2'-hydroxyphenyl)-benzoxazole (HBO) core, were studied in benzene. In general, the quantum yield for fluorescence of HBO and its analogues was small, However, the fluorescence quantum yields were determined to be 0.022,0.030, and 0.038 for G0,G2, and G3 dendrimers, respectively, increasing in higher generation dendrimers.(4)Increasing the quantum yield for generation of singlet oxygen upon photoexcitation of dendronized stilbenesSince the excited singlet state of the core moiety in stilbene-cored dendrimers G1-G4 has ca.10-ns lifetime, oxygen quenched their excited singlet state producing the singlet oxygen. The efficiency of singlet oxygen production based on the quenching of the stilbene core is the highest in G4 stilbene dendrimer.(5)Self-assembly of chromophore using amphiphilic dendronsThe self-assembly of amphiphilic pyrene-cored poly(aryl ether) dendrimers has been studied. Pyrene excimer emission from the higher generation is observed in KOH aqueous solution at low concentration. The results indicate that the self-aggregation in higher generation dendrimer takes place more efficiently than in lower generation in aqueous solution. Less