Paramagnetic endohedral fullerenes and phthalocyanine (Pc) complexes can be electron spin-active molecules. Hence they hold promise in applications where control of the electron spin properties is important such as spintronics and quantum information processing.

An important step towards these applications is the ability to tune the coupling between adjacent molecules. In this talk, I shall present our recent progress in the chemical functionalization of N@C₆₀. I shall demonstrate how we have linked N@C₆₀ and copper-phthalocyanine (CuPc) together, and characterized the resulting electron paramagnetic resonance properties, including the spin dipolar coupling between the fullerene spin and the CuPc spin. We were able to vary the distance between the two spin-active molecules and to interpret the distance-dependent coupling strength quantitatively. We then went one step further. We discovered an antiferromagnetic aggregation effect of the CuPc moieties and we demonstrated an extra facile method of tuning the dipolar coupling in such dyad systems: simply by adjusting the solution concentration. The solution concentration dependency opens a new way of tuning the dipolar coupling strength. We can turn on the dipolar coupling by diluting the sample, and turn off the dipolar coupling by concentrating the sample. I believe this to be the first step towards achieving exquisite spin-coupling control in future device architectures.