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.

This article describes the use of a progressive paper in a capstone course to develop students' writing skills. A progressive paper is one that students write one section at a time: as they add each new section, they go back and revise the previous parts based on actionable feedback from the instructor. In this course, the progressive paper takes the form of a laboratory report for a multistep synthesis. Students revise and update this paper throughout the semester. Each revision coincides with an additional step in the synthesis. This results in a complete journal-style article at the end of the semester. The students in this course show significant improvement in their writing skills throughout this process.

Inorganic materials can encapsulate organic dye molecules in a variety of ways. Those considered here are simple inorganic salts that have adsorbed, oriented, and overgrown dyes during growth from solution, which promise spectroscopic and photonic applications. The Figure shows KH2PO4 crystals in which dyes carrying sulfonate or phosphate groups have been incorporated in the {101} growth sectors (see also the cover of this issue).

For some time it had been tacitly assumed that the low thermal stability of organic molecules precluded their incorporation into inorganic matrices. This view did not survive the invention of sol-gel glasses whose relatively cold processing temperatures enabled the entrapment of dyes as well as other organic molecules.' These doped aluminosilicate glasses have shown a wide range of optical properties? including laser a~t i o n .~ We have been studying not glasses but single crystals of simple salts that contain oriented inclusions of organic dyes? These materials have a longer history5 than doped sol-gel glasses, although their uses as optical materials have not been previously considered. Herein, we describe a simple preparation of single K2S04 crystals doped with pyrene and rhodamine derivatives and their operation as blue, green, and red solid state dyeWe recently described a procedure for choosing organic guests for simple salts which involved the matching of anionic functionalities on chromophores with the anion spacings in simple salt lattices such as K2S04.4a The structures of several doped K2SO4 crystals, containing triarylmethyl (1) or pyrene (2) dyes, were determined through absorption studies with polarized light. For example, crystals containing pyranine (2a, 8-hydroxy-1,3,6-pyrenetris~lfonate)~ were typically grown by evaporating water solutions (5 x M 2a, 0.5 M K2S04). Crystals in excess of 1 cm3 were grown from seeds suspended (1) Avnir, D.; Levy, D.; Reisfeld, R. 1: A-H 0rCk 3 I Figure 1. Idealized habit of KzS04 crystal. Boundaries between "inner nucleus" and out polyhedron delineate growth sectors. This drawing indicates that 1 and 3 color the { 110) growth sectors, while 2 principally colors the (010) growth sectors.in aqueous solutions. The yellow dye was principally adsorbed in the (010) growth sectors (Figure l).9 The green luminescence was polarized parallel to [Ool]. This is consistent with OUT model in which the sulfonate groups substitute for sulfates in the lattice that are related to one another by the a and c lattice translations.The 1,3,6-trisulfonated pyrene moeity can tolerate a variety of substituents in the 8-position without interrupting the (9) Miller indices refer to ratios determined by classical goniometry where b > c ' a . (10) Dyes 2a,d were purchased from Eastman. The following dyes were prepared as described previously. 2c: Kondo, H.; Miwa, I.; Sunamoto, J. J. Phys. Chem. 1982, 86, 4826-4831. 2g: Whitaker, J. E.; Haugland, R. P.; Moore, P. L.; Hewitt, P. C.; Reese, M.;Anal. Biochem. 1991,198, 119-130. The syntheses of 2e,f,h-j were modeled after the general sulfonation procedure reported in the following. Huntress, E. H.; Carten, F. H. J. Am.(20: A solution of finely powdered 1-aminopyrene (869 mg, 4 mmol) in 10 mL of chlorosulfonic acid was stirred under argon atmosphere for 10 h at room temperature. The solution was poured on 30 g of crushed ice, and the crude product was collected by filtration, washed with 20 mL of cold water, and dried under argon to give 1.4 g of 8...

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