One of the most important objectives in materials, chemical, and physical sciences is the creation of large conjugated macrocycles with well-defined shapes, since such molecules are not only theoretically and experimentally interesting but also have potential applications in nanotechnology. Fully unsaturated macrocycles are regarded as models for infinitely conjugated π systems with inner cavities, and exhibit unusual optical and magnetic behavior. Macrocycles have interior and exterior sites, and site-specific substitution at both or either site can afford attractive structures, such as 1D, 2D, and 3D supramolecular nanostructures. These nanostructures could be controlled through the use of π-extended large macrocycles by a bottom-up strategy. Numerous shape-persistent π-conjugated macrocycles have been synthesized, but only a few are on the nanoscale. This Review focuses on nanosized π-conjugated macrocycles (>1 nm diameter) and giant macrocycles (>2 nm diameter), and summarizes their syntheses and properties.

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Eines der wichtigsten Ziele in den Materialwissenschaften, der Chemie und der Physik ist die Herstellung von großen konjugierten Makrocyclen genau definierter Form, da solche Moleküle nicht nur theoretisch und experimentell interessant sind, sondern auch potenzielle Anwendungen in der Nanotechnologie haben. Vollständig ungesättigte Makrocyclen werden als Modelle für vollständig konjugierte π‐Systeme mit Hohlräumen herangezogen. Solche konjugierten π‐Systeme zeigen aufgrund ihrer cyclischen Konjugation ein ungewöhnliches optisches und magnetisches Verhalten. Makrocyclen haben nach innen und nach außen gerichtete Bindungsstellen, und eine positionsspezifische Substitution an beiden oder nur einer der beiden Bindungsstellen kann attraktive Strukturen zugänglich machen. Von besonderer Bedeutung sind ein‐, zwei‐ und dreidimensionale supramolekulare Nanostrukturen. Um die Bildung dieser Strukturen kontrollieren zu können, bietet sich die Bottom‐Up‐Synthese ausgehend von π‐expandierten Makrocyclen an. Zahlreiche formstabile π‐konjugierte Makrocyclen wurden synthetisiert, davon aber nur eine begrenzte Zahl an nanoskaligen Vertretern. In diesem Aufsatz konzentrieren wir uns auf nanometergroße π‐konjugierte Makrocyclen (>1 nm Durchmesser) sowie Riesenmakrocyclen (>2 nm Durchmesser) und fassen deren Synthesen und Eigenschaften zusammen.

It is often claimed that evapotranspiration from urban trees can mitigate the urban heat island and adapt our cities to climate change; however, the relative effectiveness of different tree species has rarely been investigated. The current study addressed this shortcoming by comparing the growth and physiology of five commonly planted tree species: Sorbus arnoldiana, Crataegus laevigata, Malus 'Rudolph', Pyrus calleryana and Prunus 'Umineko'. The study was conducted between March and November, 2011 in eight different streets of Manchester, UK where trees had been growing for 6 years in the same growing conditions. The study showed that evapotranspirational cooling is closely related to the growth and stress tolerance of tree species. Of the species tested, Prunus 'Umineko' and P. calleryana were the fastest growing and Malus 'Rudolph' was the slowest growing. In general faster growing species showed higher leaf area index (LAI) and higher stomatal conductivity and so provided more cooling. However, Prunus 'Umineko' had surprisingly low cooling and showed signs of drought stress. P. calleryana showed up to 100 % higher stomatal conductance than the other tree species. Combining the higher LAI and wider canopy, P. calleryana and C. laevigata provided cooling up to 2.2 kW tree −1 , 3 to 4 times of cooling to that of Prunus 'Umineko' and S. arnoldiana and showed no signs of drought stress. Malus 'Rudolph' showed stress tolerance but provided low cooling. Prunus 'Umineko' and S. arnoldiana with their thin and sparse canopy provided low cooling and showed susceptibility to urban stress.

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