Salting Benzenes

Abstract

Simple salt crystals, such as potassium sulfate or barium acetate, were grown in the presence of a variety of aromatic molecules, especially aniline derivatives, bearing sulfonate or carboxylate substituents. We call this process salting, borrowing the term from Michl and co-workers who coined it in a related context (Kirkor, E.; Gebicki, J.; Phillips, D. R.; Michl, J. J. Am. Chem. Soc. 1986, 108, 7106−7107). Particular growth sectors of the resultant crystals were luminescent, and the emitted light was highly polarized indicating that the benzene derivatives were oriented inside of the salt lattices. These results are presented in the context of a generalization of single crystal matrix isolation; isomorphous matching of hosts and guests need not be a constraint. We show by polarization spectroscopy and magnetic resonance that different faces of the crystals will entrap molecules in different conformations otherwise separated by small energies in solution. Metastable triplet states are remarkably long-lived at room temperature in salt matrixes. The mechanisms of benzene derivative incorporation depend highly on secondary surface structures that are imaged by differential interference contrast microscopy. Luminescent molecules identify these features by lighting-up particular substructures and as such serve as probes of crystal growth mechanisms. We show how patterns of light in crystals are used to assign absolute growth directions. We conclude by arguing that the results herein can be extended to a limitless range of guests, while encouraging the use of salts as matrixes for the study of organic compounds.

3D visualization of additive occlusion and tunable full-spectrum fluorescence in calcite

“…Changes in excitation and emission spectra are frequently seen on the occlusion of dyes within crystals due to changes in their conformations or local environments18. For example, rhodamine19, aniline32 and pyrene-based dyes19 occluded in K 2 SO 4 show red shifts in the emission maxima, while blue shifts of absorption maxima and either red or blue shifts in emission maxima were observed for dyes incorporated within potassium dihydrogen phosphate3334. Notably, however, in addition to a small shift in the primary emission maximum, we also observe a significant increase in the intensity of a secondary peak at 550–553 nm with increasing levels of occluded dyes.…”

Structural Correspondence of Solution, Liquid Crystal, and Crystalline Phases of the Chromonic Mesogen Sunset Yellow

“…31,32,33,34 SSY in micromolar concentrations had earlier been studied in crystals of K 2 SO 4,35,36 and by our group 37,38 and others in KH 2 PO 4 .39,40,41 These mixed crystals grow at solution concentrations of SSY known to favor the formation of dimers and trimers, on their way to chromonic aggregates. 31,32,33,34 SSY in micromolar concentrations had earlier been studied in crystals of K 2 SO 4,35,36 and by our group 37,38 and others in KH 2 PO 4 .39,40,41 These mixed crystals grow at solution concentrations of SSY known to favor the formation of dimers and trimers, on their way to chromonic aggregates.…”

The Influence of Promoters and Poisons on Carbon Monoxide Adsorption on Rh(100): A DFT Study

“…Experimentally, usually only a qualitative analysis of this interaction is possible. For instance, several groups [25][26][27][28][29] have studied the CO-oxygen system. In this case it is difficult to determine an interaction energy since oxygen will react with CO to form CO 2 .…”