Lab 6.docx - UV/Vis and Fluorescence Spectroscopy of Three...

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UV/Vis and Fluorescence Spectroscopy of Three Unknown Samples Triston Wilson - [email protected] Abstract: UV/Vis and fluorescence spectroscopy was used to determine the aromatic compounds present in 3 unknown samples through emission spectras. Three unknown samples were put through UV/Vis to discover the absorption spectra to determine two excitation wavelengths to use for emission spectra. The samples were ran through a spectrofluorophotometer to obtain emission spectrums in order to compare to four known aromatic compounds and discover the identity of the samples. The ?max of unknown 1, 2, and 3 were 275 nm, 375 nm, and 375 nm, respectively. The ?Em of 1 and 3 were 470 nm and 325 nm, respectively. There were 2 ?Em at 275 nm for unknown 2, and they were 473nm and 400 nm. After comparing graphs, unknown 1 was discovered to be tetracene, unknown 2 was identified as all three molecules; naphthalene, anthracene and tetracene. Unknown three was found to resemble naphthalene. It was found that the more rings an aromatic compound had meant that a longer wavelength was needed to excite electrons in the compound. This was because a compound with many rings meant that it had more bonds, and this means it takes less energy to excite these electrons. ? Introduction: Ultraviolet and visible (UV-Vis) absorption spectroscopy is the measurement of the exhaustion of a beam of light after it passes through a sample in a spectrophotometer. Absorption measurements can be at a single wavelength or over an extended spectral range. Absorption tells tells us the level of energy needed to create an electronic transition within the molecule. So, ?max is the wavelength at which there is maximum absorption and will most likely cause a transition.
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