Synthesis and characterisation of rylene diimide dimers using molecular handcuffs.

A strategy for positioning, and loosely connecting, molecules in close proximity using mechanically interlocked handcuffs is described. The strategy is demonstrated using rylene diimides, creating dimeric structures in which two components are linked through pillar[5]arene/imidazolium rotaxanes. Investigation of the resulting molecules demonstrates intriguing and new properties that arise from placing these redox active dye molecules together, allowing interactions, whilst allowing the molecules to separate as required. In particular we observe excimer emission from a perylene diimide dimer handcuff and the formation of an unusual radical anion π-dimer upon double reduction of the same molecule. The latter exhibits a unique visible absorption profile for a PDI-based molecule. We demonstrate the flexibility of our approach by making an unprecedented mixed perylene diimide/naphthalene diimide dimer which also reveals interactions between the two components. Our synthetic strategy facilitates the creation of unusual dimeric structures and allows the investigation of intermolecular interactions and the effects they have on electronic and magnetic properties.

Restricting shuttling in bis(imidazolium) pillar[5]arene rotaxanes using metal coordination.

Metal coordination to a series of bis (imidazolium)…pillar[5]arene [2]rotaxanes through the formation of metal-carbene bonds facilitates a new strategy to restrict the shuttling motion in [2]rotaxanes. Whereas the pillar[5]arene macrocycle rapidly shuttles along the full length of the bis (imidazolium) rod for the parent [2]rotaxane, Ag(i) coordination to the imidazolium groups through the formation of N-heterocyclic carbenes leads to restricted motion, effectively confining the shuttling motion of the [2]rotaxane. The Ag(i) coordinated [2]rotaxanes can be reacted further, either removing the Ag-carbene species to recreate the parent [2]rotaxane, or reaction with more bulky Pd(ii) species to further restrict the shuttling motion through steric inhibition.

Spatial invasion of cooperation.

The evolutionary puzzle of cooperation describes situations where cooperators provide a fitness benefit to other individuals at some cost to themselves. Under Darwinian selection, the evolution of cooperation is a conundrum, whereas non-cooperation (or defection) is not. In the absence of supporting mechanisms, cooperators perform poorly and decrease in abundance. Evolutionary game theory provides a powerful mathematical framework to address the problem of cooperation using the prisoner's dilemma. One well-studied possibility to maintain cooperation is to consider structured populations, where each individual interacts only with a limited subset of the population. This enables cooperators to form clusters such that they are more likely to interact with other cooperators instead of being exploited by defectors. Here we present a detailed analysis of how a few cooperators invade and expand in a world of defectors. If the invasion succeeds, the expansion process takes place in two stages: first, cooperators and defectors quickly establish a local equilibrium and then they uniformly expand in space. The second stage provides good estimates for the global equilibrium frequencies of cooperators and defectors. Under hospitable conditions, cooperators typically form a single, ever growing cluster interspersed with specks of defectors, whereas under more hostile conditions, cooperators form isolated, compact clusters that minimize exploitation by defectors. We provide the first quantitative assessment of the way cooperators arrange in space during invasion and find that the macroscopic properties and the emerging spatial patterns reveal information about the characteristics of the underlying microscopic interactions.

Tug-of-war over reproduction in a social bee.

One of the main transitions in evolution is the shift from solitary organisms to societies with reproductive division of labour. Understanding social evolution requires us to determine how ecological, social and genetic factors jointly influence group stability and partitioning of reproduction between group members. Here we test the role of the three key factors predicted to influence social evolution by experimentally manipulating them in a social allodapine bee. We show that increased relatedness between nestmates results in more even reproduction among group members and a greater productivity per individual. By contrast, the degree of reproductive skew is not influenced by the opportunity for solitary breeding or by the potential benefits of cooperation. Relatedness also has a positive effect on group stability and overall productivity. These findings are in line with predictions of the tug-of-war models, in which the degree of reproductive division of labour is determined primarily by selfish competition between group members. The alternative view, where the degree of reproductive skew is the outcome of a social contract between potential breeders, was not supported by the data.