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 [D(2)A(2)] rhomboids (D = 2,6-bis(4-ethynylpyridine)aniline-based ligands; A = 2,9-bis[trans-Pt(PEt3)(2)NO3]phenanthrene) is described with emission wavelengths spanning the visible region (lambda(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 sigma(para) constants for the functional groups para to the aniline amine were plotted versus the wavenumber (cm(-1)) for the lambda(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.