Engineering crystals of dendritic molecules

Abstract

A detailed single-crystal X-ray study of conformationally flexible sulfonimide-based dendritic molecules with systematically varied molecular architectures was undertaken. Thirteen crystal structures reported in this work include 9 structures of the secondgeneration dendritic sulfonimides decorated with different aryl groups, 2 compounds bearing branches of both second and first generation, and 2 representatives of the first generation. Analysis of the packing patterns of 9 compounds bearing second-generation branches shows that despite their lack of strong directive functional groups there is a repeatedly reproduced intermolecular interaction mode consisting in an anchor-type packing of complementary second-generation branches of neighbouring molecules. The observed interaction tolerates a wide range of substituents in meta-and para-positions of the peripheral arylsulfonyl rings. Quantum chemical calculations of the molecule-molecule interaction energies agree at the qualitative level with the packing preferences found in the crystalline state. The calculations can therefore be used as a tool to rationalize and predict molecular structures with commensurate and non-commensurate branches for programming of different packing modes in crystal.dendrimers ͉ single-crystal X-ray ͉ sulfonimides ͉ supramolecular chemistry R evealing the interplay of noncovalent forces that direct processes of self-assembly and self-organization has been objective of numerous studies (1-4). This is central for the design and then the targeted synthesis of molecules capable of assembling into predefined supramolecular structures of practical significance. Although there are many examples in which the knowledge about the noncovalent interactions helped to arrive at predetermined complex molecular architectures (5, 6), the serendipity contributes to a large extent to supramolecular design. Once a new fascinating supramolecular structure is discovered, it is often difficult to decode the underlying principles of its assembly. In this context the crystallization of organic molecules is a specifically complicated case that remains poorly understood. Although it is now often possible with the aid of computations to predict a most favorable intermolecular interaction between molecules there is no guarantee that this particular intermolecular contact will be found in the crystal structure. Attempts at the rational design of organic crystals evolved into a nowadays well-established field of crystal engineering (7-11) that aims at general rules for crystal structure control. For the time being the field of crystal engineering has generated some knowledge that often helps to design organic crystals with desired properties. The main recipe is to use so-called ''tectons'' (12), which are small molecules with welldefined shape and strong directive functional groups, such as hydrogen-bonding units and metal-coordinating sites (13,14). In case reproducible trends in crystal packing for a given group of compounds are observed the molecules are usually sy...

Single‐Crystalline Optical Microcavities from Luminescent Dendrimers

“…The sterically bulky morphology and the prominent conformational flexibility of the dendrons make the orderly packed crystalline state quite unfavorable both entropically and enthalpically. Although there are several reports highlighting crystalline dendrimers, they are usually quite fragile and readily degrade upon evaporation of the included solvents. Therefore, dendrimers in the crystalline state have rarely been utilized for laser applications, which requires sufficiently stable materials against photo and thermal stimuli.…”

Dendronized Polymers with Aromatic Sulfonimide Dendrons

“…[15] In 2009 a collection of 13 single crystal structures of (first and) second generation aromatic sulfonimide-based dendrons were additionally reported. [11] This last report points towards a pronounced crystallization tendency of these shape-persistent dendrons consisting of only aromatic segments and sulfonimide branch units. This tendency was interesting to us for at least two reasons.…”

“…[10] For many of them similarities in the packing behavior in single crystals were observed. [11] In particular columnar packing motifs were repeatedly encountered. If such or similar motifs would also be observed if the dendrons carried a polymerizable unit, this could open the way to solid state polymerizations.…”

Single‐Crystalline Optical Microcavities from Luminescent Dendrimers

“…The sterically bulky morphology and the prominent conformational flexibility of the dendrons make the orderly packed crystalline state quite unfavorable both entropically and enthalpically. Although there are several reports highlighting crystalline dendrimers, [23,24] they are usually quite fragile and readily degrade upon evaporation of the included solvents. Therefore, dendrimers in the crystalline state have rarely been utilized for laser applications, which requires sufficiently stable materials against photo and thermal stimuli.…”