Fluorescence of iodine

S. Landau and E. Stenz examined the effect of low temp, and dissociation on the fluorescence of iodine vapour at low press. Fluorescence decreases as the temp, is raised, but does not cease at 800°. Dissociation destroys both fluorescence and the resonance spectra. It is therefore inferred that the complex vibrating system is not inherent in the atom, but in the molecule that the structure of the atom is relatively simple and that, in all probability, the absorption lines which are so characteristic of diatomic iodine and so sensitive to the action of monochromatic light, do not belong to the absorption spectrum of monatomic iodine. 

W. Steubing found that the intensity of the fluorescence of iodine vapour is weakened between the poles of a powerful electromagnet. The result has nothing to do with the Zeeman effect, and has no connection with effects produced by admixture with gases, solvents, etc. It is produced by a direct action of the magnetic field on the electrons causing the band spectrum weakening the individual vibrations. 

Fig. 19. Resonant scattering, absorption and fluorescence of iodine in a 100 pm foil of polyacetylene, CHJ j, near the Lj-absorption edge (X = 2.72 A) at h = 0.1 The very high dispersion of fluorescence and absorption at the short wavelength side of the absorption edge limits the measurement of resonance scattering to the pre-edge region of the spectrum. ( + ) f (E) S,...

Figure 37. Experimental results and least-squares fits of data (solid lines) for a Pt/C LSM covered with an electrodeposited layer of copper and an adsorbed layer of iodine. Topmost curve IL fluorescence middle curve copper Ka fluorescence bottom curve reflectivity.

Soon after Dennison had deduced from the specific-heat curve that ordinary hydrogen gas consists of a mixture of two types of molecule, the so-called ortho and para hydrogen, a similar state of affairs in the case of iodine gas was demonstrated by direct experiment by R. W. Wood and F. W. Loomis.1 In brief, these experimenters found that the iodine bands observed in fluorescence stimulated by white light differ from those in the fluorescence excited by the green mercury line X 5461, which happens to coincide with one of the iodine absorption lines. Half of the lines are missing in the latter case, only those being present which are due to transitions in which the rotational quantum number of the upper state is an even integer. In other words, in the fluorescence spectrum excited by X 5461 only those lines appear which are due to what we may provisionally call the ortho type of iodine molecule. 

The purple color and white-light fluorescence indicate that we have about the same amount of iodine in the two tubes but evidently there is a difference in certain properties. We believe that we are justified in concluding that in the reaction tube the equilibrium existing in ordinary iodine gas has been materially disturbed, and that an iodine has been produced which contains a higher percentage of the type of molecule which cannot absorb the mercury green line than in the normal mixture. 

The primary process in the vacuum ultraviolet photolysis of methylene iodide has been studied by Style and Ward,12 who observed that irradiation with light of wavelength 1250-2000 A. excites the fluorescence spectrum of iodine. Attempts to observe any appreciable delay between light absorption and fluorescence were unsuccessful, and the intensity of fluorescence was directly proportional to the light intensity and the pressure of methylene iodide. It was concluded that the excited I2 was produced in the primary process,... 

Assay procedures for dopamine which are superficially similar to the lutin procedure described above have been reported recently.266-268 The chemistry of the production of the fluorophore from dopamine is, however, somewhat different since the fluorophore is not a 5,6-dihydroxyindoxyl, it is incorrect to refer to the trihy-droxyindole fluorophore of dopamine (cf. ref. 252). Oxidation of the extracted catecholamine is usually carried out with iodine,266-268 presumably with the formation of 7-iodonorepinochrome. The aminochrome is subsequently rearranged to 5,6-dihydroxyindole (it is probable that deiodination accompanies the rearrangement in this case) by a solution of sodium sulfite in aqueous alkali the solution is acidified before measuring the fluorescence of the product (which is said to form relatively slowly and to be very stable).266-268 Irradiation of the reaction mixture with ultraviolet light accelerates the maximal development of fluorescence.266 Since acidification will produce sodium bisulfite in the reaction mixture, it is probable that the fluorophore is a 5,6-dihydroxyindole-sodium bisulfite addition complex. Complexes of this type are known to be both fluorescent and relatively stable in dilute acid solution.118 123,156 265 They also form relatively slowly.255... 

Detection is made in UV light. The yellow fluorescence of tetracyclines and their epimers in UV light is greatly enhanced by exposing the paper to ammonia vapours. They may also be detected by Ehrlich s reagent or by starch-iodine following N-chlorination (137). 

It is perhaps relevant here that the fluorescent compound formed in the hydrolysis of iodine cyclosilanes also has rings isolated by oxygen. It is significant, moreover, that two-dimensional polysilanes become fluorescent if a slight partial oxidation takes place. 

You are now to apply the thin-layer technique to a group of colorless compounds. The spots may be visualized under an ultraviolet light if the plates have been coated with a fluorescent indicator, or chromatograms may be developed in a 4-oz bottle containing crystals of iodine. During development, spots appear rapidly, but remember that they cilso disappear rapidly. Therefore, outline each spot with a pencil immediately on withdrawal of the plate from the iodine chamber. Solvents suggested are as follows ... 

Analyze your product by thin-layer chromatography. Dissolve very small samples of pure ferrocene, the crude reaction mixture, and recrystallized acetylferrocene, each in a few drops of toluene spot the three solutions with microcapillaries on silica gel plates and develop the chromatogram with 30 1 toluene-absolute ethanol. Visualize the spots under a uv lamp if the silica gel has a fluorescent indicator or by adsorption of iodine vapor. Do you detect unreacted ferrocene in the reaction mixture and/or a spot that might be attributed to diacetylferrocene ... 

Figure 1.3 Thin-layer chromatography, (a) Thin-layer of adsorbent containing a binder so that it adheres to the glass plate, (b) Glass plate the plates ate made up by spreading a thidc slurry of adsorbent on the plate, followed by drying in an oven nowadays pre-ptepared plate may be bought with the adsorbent on a plastic backing, (c) In the early days of TLC, gas jars were used but nowadays customised TLC tanks are available the inside of the tank is lined with filter paper soaked in eluent in order that the atmosphere in the tank is saturated with eluent vapour, (d) Eluent the plate is "spotted at a point which will be just above the level of the eluent, (e) The TLC plate. Many means of visualisation are possible (absorption of iodine, use of fluorescent agent on the adsorbent, concentrated sulphuric acid spray etc.) here a mixture is run against a reference standard of a key component in the mixture however it is possible to run many samples simultaneously.

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