Cooperativity in Hydrogen-Bonded Macrocycles Derived from Nucleobases

Introducing a rigid linear pi-conjugated acetylene linker into a supramolecular building block consisting of a hydrogen-bond donor side and a hydrogen-bond acceptor side yields a decrease in cooperativity in the resulting formed quartet. This follows from our Kohn-Sham molecular orbital and Voronoi deformation density analyses of hydrogen-bonded macrocycles based on guanine and cytosine nucleobases. The acetylene linker abstracts electron density from the hydrogen-bond acceptor and donor, making the hydrogen-bond acceptor more negatively charged and the hydrogen-bond donor more positively charged and hence suppressing the donor-acceptor charge transfer interaction between the interacting fragments. This, ultimately, hampers the cooperativity in the hydrogen-bonded macrocycle. We envision that these findings could open the door to new design principles for the development of novel hydrogen-bond supramolecular macrocycles. Quantum chemical analyses reveal that introducing rigid linear pi-conjugated acetylene linkers into a supramolecular building block hampers the cooperative self-assembly of hydrogen-bonded macrocycles. This effect originates from the electron abstracting capability of the linker and becomes amplified when the size of the linker increases.image