Synthesis of Photoactive Dendrimers

合成了在核心基团中具有光致变色或荧光发色团的树枝状聚合物。用Frechet等人开发的收敛合成法制备了树枝状大分子。将2当量的溴取代树枝状片段与1当量的1，2-双[2，4-二甲基-5-（4 '-羟基苯基）噻吩-3-基]全氟环戊烯或1当量的9，10-二羟甲基蒽反应。通过快速层析和重复制备薄层层析对树枝状大分子进行了纯化，我们在二噻吩基乙烯中引入了庞大的树枝状基团，以改变两种构象异构体的比例，平行和反平行，并提高环化量子产率。然而，树枝状基团（甚至第三代）没有改变两种构象的比例。这一结果表明，核部分的自由体积足够大，可用于芳基的旋转。研究了N，N-二乙基苯胺对中心蒽的荧光猝灭作用。荧光猝灭常数随代数的增加而显著降低。并对猝灭机理进行了详细的研究。

Dendrimers having a photochromic or a fluorescent chromophore in the core group were synthesized. The dendrimers were prepared by the convergent synthetic method developed by Frechet et al. Two equivalent of the bromo substituted dendric fragments were reacted with on equivalent 1,2-bis[2,4- dimethyl-5-(4'-hydroxyphenyl)thiophen-3-yl] perfluorocyclopentene or one equivalent 9,10- dihydroxymethylanthracene. The dendrimers were purified by flash chromatography and repetitive preparative TLC.We introduced bulky dendric groups into the dithienylethene in an attemp to change the ratio of two conformers, parallel and anti-parallel, and to increase the cyclization quantum yield. However, the dendric groups (even the third generation) did not alter the ratio of the two conformers. This result indicates that the free volume of the core part is large enough for the rotaion of the aryl groups. Fluorescence quenching of the core anthracene by N,N-diethylaniline was examined. Fluorescence quenching constants were dramatically decreased with the increasing generation. The quenching mechanism was studied in detail.