Aggregation of SPMs

Haley and coworkers have explored aggregation of isomeric SPMs with charge distribution biased by strong electron donors and acceptors. For example, [15]- and [14]annulenes 113-116 all form dimers in a range of solvents, but the [15]annulenes 

113 and 114 consistently show association constants about one order of magnitude higher than those of the analogous [14]annulenes 115 or 116 [48], 

7t-7t-stacking of the planar macrocycles and hydrophobic interactions between the alkyl side chains [102]. The related SPM 126 also aggregated to give nanofibrils that, when fabricated into thin films, could be used in the detection of explosives (e.g., TNT) based on fluorescence quenching [103]. 

In contrast to the work just described, in which aggregation facilitates product formation, aggregation can also lead to the demise of SPMs as a result of intermolecular close contacts that lead to polymerization. For example, Tobe and coworkers 

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