The self-assembly of chemical entities represents a very attractive way to create a large variety of ordered functional structures and complex matter. Although much effort has been devoted to the preparation of supramolecular nanostructures based on different chemical building blocks, an understanding of the mechanisms at play and the ability to monitor assembly processes and, in turn, control them are often elusive, which precludes a deep and comprehensive control of the final structures. Here the complex supramolecular landscape of a platinum(II) compound is characterized fully and controlled successfully through a combination of supramolecular and photochemical approaches. The supramolecular assemblies comprise two kinetic assemblies and their thermodynamic counterpart. The monitoring of the different emission properties of the aggregates, used as a fingerprint for each species, allows the real-time visualization of the evolving self-assemblies. The control of multiple supramolecular pathways will help the design of complex systems in and out of their thermodynamic equilibrium.

Luminescent platinum complexes have attractive chemical and photophysical properties such as high stability, emission in the visible region, high emission quantum yields and long excited state lifetimes. However the absorption spectrum of the compounds in the UV region, preventing their excitation in the harmless visible/red region, as well as the strong quenching of the luminescent triplet state, caused by dioxygen in water and biological fluids, reduces their possible applications for imaging. Therefore a possible solution to these drawbacks is to take advantage of the high tendency of such square planar compounds to self-assemble in supramolecular structures. The assemblies can be considered new chemical species with enhanced and tunable properties. Furthermore the assembly and disassembly process can be explored as a tool to obtain dynamic labels that can be applied in biomedicine. The change in color, the turn on and off of luminescence but also of the reactivity, the protection from quenching and environmental degradation are some of the attractive properties connected to the aggregation of the complexes.

Neutral Pt(II) complexes bearing tridentate dianionic 2,6-bis(1H-1,2,4-triazol-5-yl)pyridine and ancillary alkyl-substituted pyridine ligands have been synthesized and characterized. They show bright green emission, reaching 73% photoluminescence quantum yield in deareated chloroform solution, which can be assigned to a predominantly metal-perturbed ligand-centered phosphorescence. We have followed two strategies to preserve the spectral purity of the monomeric species by varying the substituents on the chromophoric or on the ancillary ligands. However, variations in the substitution patterns only modestly affected the radiative and radiationless deactivation rate constants of the monomers. Photophysical and electrochemical properties have been measured for all the complexes and correlated with calculations using time-dependent density functional theory. The electroluminescence spectra of the brightest, nonaggregating derivative showed a better color purity than that of iridium(III) tris(phenylpyridine), thus proving that aggregation was hindered in a running electroluminescent device.