Lehmann Matthias, Fischbach Ingrid, Spiess Hans Wolfgang, Meier Herbert
Institut für Organische Chemie, University of Mainz, Duisbergweg 10-14, 55099 Mainz, Germany.
J Am Chem Soc. 2004 Jan 28;126(3):772-84. doi: 10.1021/ja0366179.
Selectively deuterated, dodecyloxy substituted stilbenoid dendrimers of the first and second generation were synthesized by a convergent synthesis, using the Wittig-Horner reaction. The photochemistry and the fluorescence in the different crystalline and liquid crystalline phases were investigated. Molecules deuterated at the alpha-position of the alkoxy chains were used to study the photoreactions in the neat phases by 1H NMR. Reactions of the double bonds are exclusively observed in the liquid crystal phases. No photoreactions occur in the crystalline state. The mobility of the dendrimers was studied by means of 2H solid-state NMR spectroscopy. The onset of the photochemistry for dendrimer 1 [all-(E)-1,3,5-tris[2-(3,4,5-tridodecyloxyphenyl)ethenyl]benzene] corresponds to the increasing mobility at the Cr/LC transition. The first generation dendrimers still show large angle motion, whereas dendrimers of the second generation 2 [all-(E)-1,3,5-tris(2-[3,5-bis[2-(3,4,5-tridodecyloxyphenyl)ethenyl]phenyl]ethenyl)benzene] are restricted to librational motions. Photochemical conversion and fluorescence quenching for first and second generation dendrimers 1 and 2 increase with increasing molecular motion and reach a maximum in the isotropic phase.
采用Wittig-Horner反应，通过汇聚合成法合成了第一代和第二代选择性氘代、十二烷氧基取代的二苯乙烯类树枝状大分子。研究了其在不同晶相和液晶相中的光化学和荧光性质。使用在烷氧基链α位氘代的分子，通过1H NMR研究纯相中的光反应。仅在液晶相中观察到双键的反应。在晶态下不发生光反应。通过2H固态NMR光谱研究树枝状大分子的流动性。树枝状大分子1 [全-(E)-1,3,5-三[2-(3,4,5-三(十二烷氧基)苯基]乙烯基]苯]的光化学起始对应于在Cr/LC转变时流动性的增加。第一代树枝状大分子仍表现出大角度运动，而第二代树枝状大分子2 [全-(E)-1,3,5-三(2-[3,5-双[2-(3,4,5-三(十二烷氧基)苯基]乙烯基]苯基]乙烯基]苯]则局限于摆动运动。第一代树枝状大分子1和第二代树枝状大分子2的光化学转化和荧光猝灭随着分子运动的增加而增加，并在各向同性相中达到最大值。
