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 the dendrons 8-12) and convergent synthesis. Wittig-Horner reactions together with a protecting group technique yield monodisperse compounds of high constitutional and configurational purity. The solubility of the stiff molecules, which have primarily a disklike shape in the first and second generations 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 formula 3(2(n)-1) from 3 in the first generation (n = 1) to 93 in the fifth generation (n = 5). Consequently, the molecular mass reaches 24,000 in 1(5)b which contains 144 hexyloxy chains. An exact measurement of the mass is provided by matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry. In solution, the stilbenoid dendrimers 1(n) exhibit a strong tendency to aggregate, which increases from generation to generation. In the pure state, columnar mesophases Col(hd) (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 hindrance prevents such ordered arrangements in higher generations 1(n) (n = 3, 4, 5).
Institut fur Organische Chemie, Johannes Gutenberg-Universitat, Mainz, Germany. hmeier@mail.uni-mainz.de
H
Meier
M
Lehmann
U
Kolb