Introduction

Dendrimers represent a class of compounds which is attracting steadily increasing attention. Due to the uniformity, regularity, and symmetry, these compounds are not only aesthetically appealing, but they also possess interesting properties for various applications in materials science [118]. This chapter focuses on stilbenoid systems, which means conjugated dendrimers, whose dendrons consist of trans-stilbene building blocks. The branched units (BU) are either 3, 5-divinylphenyl groups or 3, 5-bis[2-(4-vinylphenyl)vinyl] groups. The peripheral benzene rings (P) are mostly substituted with solubilizing alkoxy or tert-butyl groups. The core (C) of the dendrimers can consist of a stilbenoid unit, too; but it can also be formed by other (aromatic) chromophores.

The general formula for such dendrimers is

where l is the number of dendrons attached to the core, m is the number of peripheral benzene rings, and (n — 1) is the normal number of the generation. The unbranched compound (n = 1) therefore has generation 0, but if the stil-benoid core itself has the same branching as the dendrons, the generation can be asigned as n; according to this suggestion, a generation 0 does not exist in the latter case.

The stilbene building blocks permit rotations around the single bonds adjacent to the double bonds, but they do not allow a backfolding of the dendrons. Therefore, the scaffold of the stilbenoid dendrimers is rigid, and the size and shape of a single dendritic particle are persistent within narrow limits. Since a trans-stilbene unit is about 0.93 nm long, the stilbenoid dendrimers represent well-defined nanoparticles with the diameter of a few nanometers.

The 1,3,5-trisubstitution of the benzene rings in the den-drons implicates a cross conjugation. The electronic interactions among core, branched units, and periphery are small; therefore, these segments can be regarded as individual chromophores. Energy transfers and charge transfers between these regions are possible. Apart from such intramolecular processes, intermolecular energy and charge exchanges should be efficient in stilbenoid dendrimers because there are no large insulating regions as, for example, in benzyl ether or propylene imine-based systems.

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