Hierarchical Self-Assembly of Luminescent Eu(III) Complexes on Silicon

We have combined the metal-coordinating features of phenanthroline with the remarkable complexing properties of tetraphosphonate (Tiiii) cavitands towards N-methylammonium salts with the aim of assembling novel luminescent ternary complexes. The formation of such complexes was first tested in solution: the charged sarcosine derivative 1, bearing a phenanthroline moiety, was complexed by the cavitand Tiiii-A, followed by coordination of EuIII–tris(β-diketonate) complex 2. The occurrence of the self-assembly has been proven by NMR spectroscopy, mass spectrometry and photophysical measurements. The transfer of this binding protocol to the surface showed the complete orthogonality of these interactions, as verified by control experiments on complexation inactive surfaces. The formation of the ternary complexes on the silicon surface was monitored by means of X-ray photoelectron spectroscopy and luminescence spectroscopy. The emission properties of the silicon-bound Si-Tiiii-B·1·2 and the corresponding ternary complex Tiiii-A·1·2 in solution are similar, which indicates that the transfer of the self-assembly process onto silicon does not significantly perturb the EuIII coordination environment. The self-assembly protocol illustrated here can be extended to a wide variety of lanthanide ions and can be implemented for applications in sensing, bioimaging and optoelectronic devices.