Stilbenoid dendrimers

The first five generations of the stilbenoid dendrimers 1(n) (n =1-5) have been prepared by a combined coupled synthesis (between the generations of t he dendrons 8-12) and convergent synthesis. Wittig-Horner reactions togethe r with a protecting group technique yield monodisperse compounds of high co nstitutional and configurational purity. The solubility of the stiff molecu les, which have primarily a disklike shape in the first and second generati ons and a cylindrical shape in the third, fourth, and fifth generations, is governed by the alkoxy chains that are attached to the peripheral benzene rings. The number of stilbene building blocks increases according to the fo rmula 3(2(n)-1) from 3 in the first generation (n=1) to 93 in the fifth gen eration (n = 5). Consequently, the molecular mass reaches 24000 in 1(5)b wh ich contains 144 hexyloxy chains. An exact measure-ment of the mass is prov ided by matrix-assisted laser desorption ionization time-of-flight (MALDI-T OF) mass spectrometry In solution, the stilbenoid dendrimers 1(n) exhibit a strong tendency to aggregate, which increases from generation to generatio n. In the pure stale, columnar mesophases Colhd (1(1)b, 1(1)c, 1(2)b, and 1 (2)c) and Col(ob) (1(2)b, 1(2)c) are formed; intramolecular steric hindranc e prevents such ordered arrangements in higher generations 1(n) (n=3, 4, 5) .