A 50 mM solution of p-phenylenebis(diazonium) salt (PPBD-2PF6 or PPBD-2BF4) was prepared in acetonitrile, water, or the ionic liquid bmim-BF4. The solution or suspension was sonicated 30 seconds in a laboratory ultrasound bath and filtered through a 0.45 micron PTFE syringe filter. This filtration step should not be omitted, as suspended salt particles may adsorb to the surface and affect the following step.