Ligand structures : ?Say something here!

1. Materials: All materials were provided courtesy of Wilmington College, and purchased from Sigma-Aldrich, Fisher Scientific, Experimental: Samples were prepared by combining excess amount of ligating compound with the metal compound in vials, and dissolving in a solvent if necessary. Once all samples had been made, filter paper was sectioned off into eighths and used as the carrier material for each sample, as it (what?) showed minimal fluorescence. Each sample was pipetted onto a section of filter paper, and any solvent or extra liquid was allowed to evaporate. Qualitative data were recorded as the ligand-metal saturated paper was then irradiated with ultraviolet light, followed by an immersion in liquid nitrogen and subsequent irradiation with ultraviolet light. After these data were recorded, the paper was gently heated to potentially remove any extra ligands. How do you know only “extra ”ligands were removed?Once the heating was complete, the filter paper was allowed to return to room temperature and the room and liquid nitrogen temperature irradiation data were recorded. Table 1: Qualitative analysis of fluorescence of various ligand-metal complexes, ordered by ligating compound. Superscript letters indicate solvent in the case of dry complexes (A for acetone, D for dichloromethane, and N for Acetonitrile. Furthermore, bolded luminescence data indicate increased intensity but no change in wavelength, while italicized compounds indicate a molecule lacking a metal center. “Weak” fluorescence is determined as barely observable, while “none” is characterized as having no discernible fluorescence. Introduction: When electrons in an excited state return to a lower energy level, they give off photons in a phenomenon called luminescence. When the cause of a molecule’s luminescence is another photon of higher wavelength (and thus higher energy) than the emitted photon, the luminescence is further classified into fluorescence. One method of such excitation involves irradiating the compound with ultraviolet light, as shown in Figure 1. Once in the excited state, any form of energy transfer, including collision with other molecules, lessens or can even destroy a molecule’s fluorescence. A common method of reducing thermal vibrations of molecules is by immersing the substance in liquid nitrogen, which has a boiling point of 77 Kelvin (-196°C). Figure 1: mechanism of fluorescence; excitation of an electron by and emission of a photon. While many compounds fluoresce when chilled with liquid nitrogen, there are also many examples of compounds that fluoresce at room temperature (295-300 Kelvin). Substances that are capable of fluorescing at room temperature can have a different fluorescence at liquid nitrogen temperature. One such compound is pyridine copper (I) iodide, (C5H5N)nCuI, which shows intense yellow fluorescence at room temperature. When chilled to liquid nitrogen temperature, however, reduction of thermal vibrations allow for the emission of higher energy pink-purple photons, which are otherwise quenched. This evidences? that it is possible to utilize temperature to control the wavelength, and thus the color, of a molecule’s fluorescence, and is the basis of the research done here. A B C D Figure 2: A: luminescence of bis-pyridine copper (I) iodide at room temperature. B: luminescence of bis-pyridine copper (I) iodide chilled in liquid nitrogen. C: luminescence of pyridine copper (I) iodide at room temperature. D: luminescence of pyridine copper (I) iodide chilled in liquid nitrogen. Are these pictures you took? If so say so. Ligand structures: ?Say something here! pyridine 2,2’-bipyridine triphenylphosphine Ethylenediamine 2-Benzylpyridine 2,6-diaminopyridine Benzil Results, Conclusions, and Future Work: Two compounds, benzil and diaminopyridine, were shown to have significant fluorescence in absence of a metal complex. Generally, metal complexes with nitrates showed little to no fluorescence, and one complex even absorbed ultraviolet light. Compounds that coordinated with an odd number of aromatic rings (such as pyridine or triphenylphosphine) generally fluoresced more reliably than other complexes. Copper-halides complexes tend to fluoresce very well, especially when pyridine is used as the ligating compound. For several complexes, however, there are not enough data to support any generalized statement. Future work would involve quantitative analysis of fluorescent compounds, broadening the scope of ligating compounds investigated, as well as increasing the number of metal-halide centers. Acknowledgement: Wilmington College provided funding for the materials for this work. Who was/were you advisor(s)? References: 1. Ford P. and Vogler A. Acc. Chem. Res. 1993, 26, 220-2262. Tardet al. Chem. Mater. 2008, 20, 7010–70163. Knotteret al. Inorg. Chem. 1992, 31, 2196-22014. Perruchaset al. Inorg. Chem. 2011, 50, 10682–10692 5. Kyle et al. J. Am. Chem. Soc. 1991, 113, 2954-2965 6. Dias et al. J. Am. Chem. Soc. 2003, 125, 12072-12073 Fluorescence Thermochromism: Qualitative AnalysisJacob Barrett, Michael J. Goldcamp, Alfred Conklin, Jr.Wilmington College, Wilmington, Ohio, 45177