Tunable visible light emission of self-assembled rhomboidal metallacycles

Supramolecular coordination complexes (SCCs) have been proposed for applications necessitating photon emitting properties; however, two critical characteristics, facile tunability and high emission quantum yields, have yet to be demonstrated on SCC platforms. Herein, a series of functionalized D _2h [D₂A₂] rhomboids (D = 2,6-bis(4- ethynylpyridine)aniline-based ligands; A = 2,9-bis[trans-Pt(PEt ₃)₂NO₃]phenanthrene) is described with emission wavelengths spanning the visible region (λ_max = 476-581 nm). Tuning was achieved by simple functional group modifications para to the aniline amine on the donor building block. Steady-state absorption and emission profiles were obtained for each system and are discussed. When the Hammett σ_para constants for the functional groups para to the aniline amine were plotted versus the wavenumber (cm^-1) for the λ_max of the emission profile, a linear relationship was observed. By utilizing this relationship, the emission wavelength of a given rhomboid can be predetermined on the basis of the Hammett constant of the functionality employed on the donor precursor. This range of visible light emission for a suite of simple rhomboids along with the predictive nature of the wavelength of emission is unprecedented for these types of systems.