双枝芳醚树枝形聚合物构象研究

Conformation Study of bis-Dendron Poly(aryl ether) Dendrimers

合成了外围只以一个芘基团修饰、核心为苯胺的双枝芳醚树枝形聚合物Py-[Gn]2-NPh(n=1～2),利用分子内电子转移和激基复合物的形成对其折叠构象和折叠程度进行了研究.二氯甲烷溶液中选择性激发芘基团,树枝形聚合物Py-[Gn]2-NPh分子内发生从苯胺到芘基团之间的电子转移,观察到了分子内外围芘基团和核心苯胺基团之间形成激基复合物的发光,为芳醚树枝形聚合物折叠构象的存在给出了直接实验观察.二氯甲烷溶液中1～2代Py-[Gn]2-NPh分子内电子转移效率分别为0.87和0.81,速率常数分别为2.3×108和1.5×108s-1.利用电子转移速率常数估算得到1～2代Py-[Gn]2-NPh分子内给、受体之间的距离分别为0.79和0.81nm,说明双枝芳醚树枝形聚合物与单枝结构类似,其外围基团也可以折叠到达分子内部接近核心的位置.

bis-Dendron poly（aryl ether） dendrimers Py-[Gn]2-NPh （n= 1-2） with only one pyrene chromophore at the periphery and an anilino group at the core were synthesized and the extent of folding back conformation was given by the intramolecular electron transfer and exciplex formation. Selective excitation of the periphery pyrene moiety of Py-[Gn]2-NPh in dichloromethane results in an electron transfer process from aniline moiety to pyrene group, and as a consequence of the electron transfer an intramolecular exciplex is formed. Since the exciplex formation requires a direct orbital overlap between the donor and the acceptor groups, this gives us a directly experimental observation for the folding back conformation of bis-dendron poly（aryl ether） dendrimers. The efficiencies and the rate constants of electron transfer in di- chloromethane are 0.87, 0.81 and 2.3 × 10^8, 1.5 × 10^8 s^-1 for generations 1-2, respectively. The distances between the donor and acceptor （center to center） were estimated from the rate constants of electron transfer to be, 0.79 and 0.81 nm for genertions 1-2, respectively. This means that the periphery chromophores can fold inward and reach the core vicinity for Py-[Gn]2-NPh, which is similar to the mono-dendron dendrimers Py-Gn-NHPh.