Uniquely versatile: nano-site defined materials based on polyphenylene dendrimers

Türp, David; Nguyen, Thi‐Thanh‐Tam; Baumgarten, Martin; Müllen, Kläus

doi:10.1039/c1nj20449a

“…15 The build-up of a homologous series of rylene dyes (Figure 1) has enabled a systematic variation of absorption and emission wavelengths reaching far into the near infrared. Since the new opportunities for device fabrication have been extensively described elsewhere, 8 here, I focus on the role of these chromophores as stimuli for nanoscience. As expected, increases in the ribbon size up to 4 nm in length required the substitution of alkyl chains at the imide, as well as the ring positions to achieve soluble materials.…”

Section: Rylene Chromophoresmentioning

confidence: 99%

Evolution of Graphene Molecules: Structural and Functional Complexity as Driving Forces behind Nanoscience

Müllen

¹

2014

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Abstract:The evolution of nanoscience is based on the ability of the fields of chemistry and physics to share competencies through mutually beneficial collaborations. With this in mind, in this Perspective, I describe three classes of compounds: rylene dyes, polyphenylene dendrimers, as well as nanographene molecules and graphene nanoribbons, which have provided a superb platform to nurture these relationships. The synthesis of these complex structures is demanding, but also rewarding because they stimulate unique investigations at the singlemolecule level by scanning tunneling microscopy and single-molecule spectroscopy. There are close functional and structural relationships between the molecules chosen. In particular, rylenes and nanographenes can be regarded as honeycombtype, discoid species composed of fused benzene rings. The benzene ring can thus be regarded as a universal modular building block. Polyphenylene dendrimers serve, first, as a scaffold for dyes en route to multichromophoric systems and, second, as chemical precursors for graphene synthesis. Through chemical design, it is possible to tune the properties of these systems at the single-molecule level and to achieve nanoscale control over their self-assembly to form multifunctional (nano)materials.

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“…This stands in marked contrast to the situation prevailing in dendrimers made from conformationally flexible repeat units [182,183]. Indeed, the semirigid character of the PPD scaffolds leads to a perfect nanosite definition of functional groups [190] such as chromophores [196,197], catalysts [190,198,199], or electrolytes [200] at the core, in the scaffold, or on the rim of the dendrimers [201]. Although these aspects are beyond the scope of the present text, it should be mentioned that polyphenylene dendrimers, due to their unique structure and functionalization, have served, for example, as light harvesting complexes [133,202], receptors for gas sensing [203,204], and carrier systems for crossing the blood-brain barrier [205,206].…”

Section: Scheme 8 Synthesis Of the Giant Hexagonal Pah C222 28mentioning

confidence: 91%

“…This realization stimulated us to synthesize larger and larger polyphenylene dendrimers by both convergent and divergent approachs [187][188][189]. For the divergent approach (e.g., layer-by-layer synthesis), the AB 2 -type branching reagent 33 turned out of be crucially important [190]. Indeed, the diene unit of this AB 2 system could react with any multiethynyl core to furnish new pentaphenyl benzene moieties in a Diels-Alder cycloaddition with expulsion of carbon monoxide (Scheme 10).…”

Section: Scheme 8 Synthesis Of the Giant Hexagonal Pah C222 28mentioning

confidence: 99%

Graphene as a Target for Polymer Synthesis

Müllen

¹

2013

Advances in Polymer Science

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Graphene has remarkable physical properties, but existing production methods have severe deficiencies that limit its potential use in robust technologies. Opening a reliable and efficient synthetic route to graphene and its functionalized derivatives offers a path to overcome this obstacle for its practical application. Graphene can be regarded as a two-dimensional polymer (2D), and it is here argued that it, along with its derivatives, represents a realistic yet challenging target for polymer synthesis.In order to demonstrate the possibility of such syntheses, an overview is presented on the evolution of phenylene-based macromolecules. It is shown how classical linear polyphenylenes can be expanded to increasingly more sophisticated structures involving two-and three-dimensional (3D) polyphenylene architectures. A crucial aspect of the meticulous synthetic design of these molecules has been the avoidance of defects within the structures, resulting in the precise control of their physical, especially optoelectronic, properties.Linear conjugated polymers with defined optical properties have been made by controlling the degree of torsion between the benzene rings. This has included the development of efficient routes to ladder-type polymers and of step-ladder materials. Planar graphene molecules, or nanographenes, in a range of sizes and shapes have been fabricated by the controlled cyclodehydrogenation of 3D polyphenylene dendrimers. By combining knowledge gained from the synthesis of conjugated polymers, polyphenylene dendrimers, and nanographenes, it has proven feasible to make, either by solution or surface-bound methods, graphene nanoribbons with well-defined structures. These functional materials possess properties similar to graphene while displaying improved processability.Finally, we review less-sophisticated paths towards graphene materials involving processing of graphene oxide, its reduction, and its hybridization with other components. These too have a role to play in acquiring functional graphenes where K. Müllen (*) Max-Planck-Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany e-mail: muellen@mpip-mainz.mpg.de a lesser degree of control over the properties is required. This voyage of exploration towards the precise synthesis of conjugated phenylene-based polymers has thus had the dual objectives of fundamental research and practical materials science. En route we have had to meet the sometimes conflicting gauntlets thrown down by these two aims, which has at times involved trade-offs between the theoretically desirable and the reasonably accessible.

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“…This stands in marked contrast to the situation prevailing in dendrimers made from conformationally flexible repeat units [182,183]. Indeed, the semirigid character of the PPD scaffolds leads to a perfect nanosite definition of functional groups [190] such as chromophores [196,197], catalysts [190,198,199], or electrolytes [200] at the core, in the scaffold, or on the rim of the dendrimers [201]. Although these aspects are beyond the scope of the present text, it should be mentioned that polyphenylene dendrimers, due to their unique structure and functionalization, have served, for example, as light harvesting complexes [133,202], receptors for gas sensing [203,204], and carrier systems for crossing the blood-brain barrier [205,206].…”

mentioning

confidence: 86%

“…This realization stimulated us to synthesize larger and larger polyphenylene dendrimers by both convergent and divergent approachs [187][188][189]. For the divergent approach (e.g., layer-by-layer synthesis), the AB 2 -type branching reagent 33 turned out of be crucially important [190]. Indeed, the diene unit of this AB 2 system could react with any multiethynyl core to furnish new pentaphenyl benzene moieties in a Diels-Alder cycloaddition with expulsion of carbon monoxide (Scheme 10).…”

mentioning

confidence: 99%

Hierarchical Macromolecular Structures: 60 Years after the Staudinger Nobel Prize II

2013

Advances in Polymer Science

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Uniquely versatile: nano-site defined materials based on polyphenylene dendrimers

Cited by 63 publications

References 161 publications

Evolution of Graphene Molecules: Structural and Functional Complexity as Driving Forces behind Nanoscience

Evolution of Graphene Molecules: Structural and Functional Complexity as Driving Forces behind Nanoscience

Graphene as a Target for Polymer Synthesis

Hierarchical Macromolecular Structures: 60 Years after the Staudinger Nobel Prize II

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