Aiming at the development of new architectures within the context of the quest for strongly luminescent materials with tunable emission, we utilized the propensity of the robust bimetallic clusters [Au2Ag 2(RI/RII)4] (RI = 4-C6F4I, RII = 2-C6F 4I)for self-assembly through aurophilic interactions. With a de novo approach that combines the coordination and halogen-bonding potential of aromatic heteroperhalogenated ligands, we have generated a family of remarkably luminescent bimetallic materials that provide grounds to address the relevance, relative effects, and synergistic action of the two interactions in the underlying photophysics. By polymerizing the green-emitting (λ maxem = 540 nm) monomer [Au2Ag2R II4(tfa)2]2- (tfa = trifluoroacetate) to a red-emitting (λmaxem = 660 nm) polymer [Au2Ag2RII4(MeCN)2] n, we demonstrate herein that the degree of cluster association in these materials can be effectively and reversibly switched simply by applying mechanochemical and/or vapochemical stimuli in the solid state as well as by solvatochemistry in solution, the reactions being coincident with a dramatic switching of the intense, readily perceptible photoluminescence. We demonstrate that the key event in the related equilibrium is the evolution of a metastable yellow emitter (λmaxem = 580 nm) for which the structure determination in the case of the ligand RII revealed a dimeric nonsolvated topology [Au2Ag2RII 4]2. Taken together, these results reveal a two-stage scenario for the aurophilic-driven self-assembly of the bimetallic clusters [Au2Ag2(RI/RII)4]: (1) initial association of the green-emitting monomers to form metastable yellow-emitting dimers and desolvation followed by (2) resolvation of the dimers and their self-assembly to form a red-emitting linear architecture with delocalized frontier orbitals and a reduced energy gap. The green emission from [Au2Ag2RII4(tfa)2] 2- (λmaxem = 540 nm) exceeds the highest energy observed for [Au2Ag2]-based structures to date, thereby expanding the spectral slice for emission from related structures beyond 140 nm, from the green region to the deep-red region.
ASJC Scopus subject areas
- Colloid and Surface Chemistry