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Fluorescence Study of the Kinetics of Energy Transfer Between Dyes 1 Introduction Coumarin 1 and Sodium fluorescein are two dyes which absorb and emit light in the visible region By using a spectrophotometer we are recording an absorption spectrum and then determining the molar decadic absorption coefficients which will be used later to interpret and analyse the fluorescence spectra For fluorescence spectra there are two kinds the excitation and the emission spectrum The excitation spectrum is obtained by measuring the intensity of the emission as the excitation wavelength is altered by scanning a monochromator The emission spectrum is obtained by measuring the emission intensity as a function of wavelength for excitation at a fixed wavelength An absorption spectrum and an excitation spectrum are by their nature actually equivalent The two dyes exhibit energy transfer properties The donor is coumarin and the acceptor the fluorescein When the donor is excited it is naturally decaying to the ground state However in presence of an acceptor this process is enhanced trough energy transfer We will distinguish between collisional energy transfer and dipole-dipole transfer From here we will try to determine the quenching constant and the distance at which decay and energy transfer are equally probable as well as prove that Stern-Volmers law and Frsters theory are obeyed 2 Results 21 Electronic Absorption Spectra We made up stock solutions for both salts and diluted them down to use in the UVvis spectrometer Coumarin 1 C 8 x10-5 mol dm -3 We obtained a spectrum with a maximum at 3765nm at an absorbance of 14573 using Beer-Lamberts law we deduced the molar decadic absorption coefficients Sodium fluorescein C 2425 x10-5 mol dm -3 Here max was 5005 nm at an absorbance of 20922 Summary of the results obtained Dye max nm max m2 mol-1 m2 mol-1 m2
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