Rhodamine

Commercial rhodamine consists principally of the phthalei n of diethylmetamidophenol. The condensation of metamidophenol (and its derivatives) with phthalic anhydride only takes place in presence of strong sulphuric acid. 

Rhodamines may also be prepared by action of dimethyl- or diethylamine on the chloride formed on treating fluorescein with phosphorus oxychloride. 

The constitution of the simplest rhodamine is probably analogous to that of fluorescein, and is expressed by the formula — 

Unlike the ordinary phthaleins, rhodamine possesses basic and acid properties. It forms soluble salts, from which the base is not separated by alkalies. The solutions are turned yellow by an excess of mineral acid. 

The shade of rhodamine is a magnificent red, and exhibits on silk a hitherto unrivalled fluorescence. 

The base of the dye is a red powder, which is insoluble in water, but soluble in alcohol producing a red solution. The HCl salt, which is sold on the market as Rhodamine B , is a very fine violet black powder with yellow green fluorescence soluble in water to produce a deep red violet colour also soluble in alcohol producing a red solution melts at 270°C, boils at 310°C, but it begins to smoke gradually with the temperature rise from the melting point and is carbonized partly without vaporizing. The smoke particles of rhodamine B from a smoke composition are insoluble in water. 

The solution of rhodamine B is acid, the pH value being 2.5 3.0 for a 1% solution in water, but its use in combination with chlorate does not cause any trouble. This dye has a serious defect in that it stains everything that comes into contact with it. 

The base, which is insoluble in water, can be used for smoke in place of the HCl salt, but it burns less easily than the smoke composition which contains the HCl salt. Moreover the base is not as cheap as the HCl salt because the manufacturing plant has to be modified for the purpose. 

Manufacture. Rhodamine B is obtained by condensation of diethyl-m- aminophenol with phthalic anhydride. 

The additive name B means blue and this dye which contains no filler is called often Rhodamine B cone . 

CA Index Name Xanthylium, 9-[2-(ethoxycarbonyl) phenyl]-3,6-bis(ethylamino)-2,7-dimethyl-, chloride (1 1) 

6G chloride Rhodamine 6GB Rhodamine 6GBN Rhodamine 6GD Rhodamine 6GDN Rhodamine 6GDN Extra Rhodamine 6GEx ethyl ester Rhodamine 6GH Rhodamine 6GO Rhodamine 6GX Rhodamine 6JH Rhodamine 6JH-SA Rhodamine 6JH-SA Extra 1150 Rhodamine 6Zh-DN Rhodamine F 5G Rhodamine F 5GL Rhodamine GDN Rhodamine GDN Extra Rhodamine Y 20-7425 Rhodamine Zh Silosuper Pink B Vali Fast Red 1308 

Merck Index Number Not listed Cbemical/Dye Class Xanthene Molecular Formula C28H31CIN2O3 Molecular Weight 479.02 

Physical Form Red-brown or maroon powder or crystals 

Solubility Soluble in water, ethanol, methanol Melting Point 290 °C Absorption (Amax) 528 nm Emission (Amax) 551 nm Synthesis Synthetic methods  

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It condenses with resorcinol and amino-phenols to give phthalein and rhodamine dyestuffs respectively. Esters are used in the formation of polyimides. ... 

Figure Bl.22.7. Left resonant seeond-hannonie generation (SHG) speetnimfrom rhodamine 6G. The inset displays the resonant eleetronie transition indueed by tire two-photon absorption proeess at a wavelength of approximately 350 mn. Right spatially resolved image of a laser-ablated hole in a rhodamine 6G dye monolayer on fiised quartz, mapped by reeording the SHG signal as a fiinetion of position in the film [55], SHG ean be used not only for the eharaeterization of eleetronie transitions within a given substanee, but also as a mieroseopy tool.

Figure C 1.5.5. Time-dependent fluorescence signals observed from liquid solutions of rhodamine 6G by confocal fluorescence microscopy. Data were obtained with 514.5 mn excitation and detected tlirough a 540-580 nm...

Figure C 1.5.7. Surface-eiilianced Raman spectra of a single rhodamine 6G particle on silver recorded at 1 s intervals. Over 300 spectra were recorded from this particle before tlie signals disappeared. The nine spectra displayed here were chosen to highlight several as yet unexplained sudden changes in botli frequency and intensity. Reprinted witli pennission from Nie and Emory [ ]. Copyright 1997 American Association for tlie Advancement of Science.

Michaels A M, Nirmal M and Brus L E 1999 Surface enhanced Raman spectroscopy of individual rhodamine 6G molecules on large Ag nanocrystals J. Am. Chem. See. 121 9932-9... 

Bromophenol blue 2, 7 -DichIorofluorescein Eosin, tetrabromofluorescein Fluorescein Potassium rhodizonate, C404(0K)2 Rhodamine 6G Sodium 3-aIizarinsuIfonate Thorin Dissolve 0.1 g of the acid in 200 mL 95% ethanol. Dissolve 0.1 g of the acid in 100 mL 70% ethanol. Use 1 mL for 100 mL of initial solution. See Dichlorofluorescein. Dissolve 0.4 g of the acid in 200 mL 70% ethanol. Use 10 drops. Prepare fresh as required by dissolving 15 mg in 5 mL of water. Use 10 drops for each titration. Dissolve 0.1 g in 200 mL 70% ethanol. Prepare a 0.2% aqueous solution. Use 5 drops per 120 mL endpoint volume. Prepare a 0.025% aqueous solution. Use 5 drops. 

Figure 9.17 illustrates these features in the case of the dye rhodamine B. The maximum of the typically broad Sj — Sq absorption occurs at about 548 nm with a very high value of... 

Figure 9.17 Absorption and fluorescence spectra of rhodamine B in methanol (5 X 10 mol 1 ). The curve marked is for the J 2 absorption (process 8 in Figure 9.18) and that marked 5 for process 1. (Reproduced, with permission, from Dienes, A. and Shank, C. Y, Chapter 4 in Creation and Detection of the Excited State (Ed. W. R. Ware), Vol. 2, p. 154, Marcel Dekker, New York, 1972)...

For uniformity with the stmctures given in the Colourindex the ammonium radical (9) is used for the amino-substituted xanthenes and the keto form for the hydroxy derivatives. The xanthene dyes may be classified into two main groups diphenylmethane derivatives, called pyronines, and triphenylmethane derivatives (eg, (4)), which are mainly phthaleins made from phthaUc anhydride condensations. A third much smaller group of rosamines (9-phenylxanthenes) is prepared from substituted ben2aldehydes. The phthaleins may be further subdivided into the following fluoresceins (hydroxy-substituted) rhodamines (amino-substituted), eg, (6) and mixed hydroxy/amino-substituted. 

The physical properties of the xanthene type dye stmcture in general have been considered. For example, the aggregation phenomena of xanthene dyes has been reviewed (3), as has then photochemistry (4), electron transfer (5), triplet absorption spectra (6), and photodegradation (7). For the fluoresceins in particular, spectral properties and photochemistry have been reviewed (8), and the photochemistry of rhodamines has been investigated (9). 

Rhoda.mines, Rhodamines are commercially the most important arninoxanthenes. If phthalic anhydride is used in place of formaldehyde in the above condensation reaction with y -dialkylarninophenol, a triphenyknethane analogue, 9-phenylxanthene, is produced. Historically, these have been called rhodamines. Rhodamine B (Basic Violet 10, Cl45170) (17) is usually manufactured by the condensation of two moles of y -diethylaminophenol with phthahc anhydride (24). An alternative route is the reaction of diethylamine with fluorescein dichloride [630-88-6] (3,6-dichlorofluoran) (18) under pressure. 

The free base of compound (17) is Rhodamine B base [509-34-2] (Solvent Red 49 Cl 45170 1). The phosphotungstomolybdic acid salt of (17) is Pigment Violet 1 [1326-03-0] Cl45170 2). Pigment Red 173 [12227-77-9] Cl45170 3) is the corresponding aluminum salt. 

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