Luminescent characterization of solution oligomerization process mediated gold-gold interactions.: DFT calculations on [Au2Ag2R4L2]n moieties

The optical properties of [Au2Ag2(C6F5)(4)(OCMe2)(2)](n) (1) have been studied in the solid state at room temperature and at 77 K and in acetone solution (5 x 10(-4) M). The crystal structure of 1, analyzed by X-ray diffraction, consists of polymeric chains formed by repetition of Au2Ag2 moieties linked through short gold-gold interactions. The emission profile observed for 1 in dilute acetone solution (5 x 10(-4) M) is assignable to pentafluorophenyl localized pi pi* excited states or from pi-MMCT transitions, and in the solid-state arises from metal-centered (d sigma*)(1)(p sigma)(1) or (d delta*)(1)(p sigma)(1) excited states. When the absorption and emission spectra of compound 1 in acetone are registered at different concentrations, they display a band that does not obey the Lambert-Beer law. This deviation is consistent with molecular aggregation in solution through gold-gold interactions, and a clear correlation between the emission wavelength and the structure of 1 in the solid state and in solution is shown. DFT calculations accord with the observed experimental behavior and show the nature of the orbitals involved in each transition.