Fluorescence with triethylamine

In a recent study, Singer221 showed that triethylamine quenches fluorenone fluorescence with a greater efficiency in more polar solvents. According to Eq. (28), this could be caused by an increase in kes or by a decrease in kz. Since the fluorescence yield of fluorenone was also found to increase dramatically in more polar solvents, it is clear from Eq. (27) that ks must decrease. This was rationalized with the idea that increasing solvent polarity reorders the electronic states so that intersystem crossing changes from (7r 1,7r) —> (tt 3,m) to ( 7r 1,7r) -> (ir 3,ir). According to EI-Sayed,222 the former can be as much as 103 faster than the latter which would raise the lifetime and fluorescence quantum yield in polar solvents. 

Specific examples of electron transfer studies made include a time resolved spectroscopic investigation of CT complexes of 2-naphthol with triethylamine in polar and non-polar solvents , fluorescence quenching of carbazole and indole by ethylene thiodicarbonate which forms ground state complexes , and the luminescent charge transfer complex of 4,4 -bipyridinium ion with tetrakis [3.5-bis(trifluoromethyl)phenyl]borate anion . 

Column Lichrosorb RP8 7 ym (250x3 mm ID), mobile phase methanol - water - formic acid (166 34 1) buffered with triethylamine at pH 8.5, flow rate 1 ml/min, detection UV 330 nm (a), fluorescence (excitation 304 nm, emission 355 nm)(b) and fluorescence (excitation 396 nm, emission 475 nm)(c). Peaks 1, harmol 2, harmalol 3, harmine 4, harmaline. 

The interaction of the 2,3-bis(5 -formylpyrrol-2 -yl)quinoxaline 74a easily obtainable from l,2-bis(lff-pyrrol-2-yl)ethane-l,2-dione 62a via 2,3-bis(l/l-pyirol-2-yl)quinoxaline 130a, with equimolar amounts of 1,3-diaminopropane (or 1,4-diaminobutane) in boiling methanol with triethylamine form the macrocycles 141a, b (Scheme 5.33). Both compounds display selective and sensitive fluorescence quenching responses toward Hg " ion in aqueous solution (Wang et al. 2005a, b). 

Milbemectin consists of two active ingredients, M.A3 and M.A4. Milbemectin is extracted from plant materials and soils with methanol-water (7 3, v/v). After centrifugation, the extracts obtained are diluted to volume with the extraction solvent in a volumetric flask. Aliquots of the extracts are transferred on to a previously conditioned Cl8 solid-phase extraction (SPE) column. Milbemectin is eluted with methanol after washing the column with aqueous methanol. The eluate is evaporated to dryness and the residual milbemectin is converted to fluorescent anhydride derivatives after treatment with trifluoroacetic anhydride in 0.5 M triethylamine in benzene solution. The anhydride derivatives of M.A3 and M.A4 possess fluorescent sensitivity. The derivatized samples are dissolved in methanol and injected into a high-performance liquid chromatography (HPLC) system equipped with a fluorescence detector for quantitative determination. 

High Performance Liquid Chromatographic (HPLC) Analysis. A Waters HPLC system (two Waters 501 pumps, automated gradient controller, 712 WISP, and 745 Data module) with a Shimadzu RF-535 fluorescence detector or a Waters 484 UV detector, and a 0.5 pm filter and a Rainin 30 x 4.6 mm Spheri-5 RP-18 guard column followed by a Waters 30 x 3.9 cm (10 pm particle size) p-Bondapak C18 column was used. The mobile phase consisted of a 45% aqueous solution (composed of 0.25% triethylamine, 0.9% phosphoric acid, and 0.01% sodium octyl sulfate) and 55% methanol for prazosin analysis or 40% aqueous solution and 60% methanol for naltrexone. The flow rate was 1.0 mL/min. Prazosin was measured by a fluorescence detector at 384 nm after excitation at 340 nm (8) and in vitro release samples of naltrexone were analyzed by UV detection at 254 nm. 

The crucial requirement of excited-state proton transfer (ESPT) is suggested by the failure of 1-naphthyl methyl ether to undergo self-nitrosation under similar photolysis conditions. The ESPT is further established by quenching of the photonitrosation as well as 1-naphthol fluorescence by general bases, such as water and triethylamine, with comparable quenching rate constants and quantum yield. ESPT shows the significance in relation to the requirement of acid in photolysis of nitrosamines and acid association is a photolabile species. 

FIGURE 10. Relative quantum yields for exciplex fluorescence (filled symbols) and addition product formation (open symbols) versus solvent dielectric constant for trans-stilbene with di isopropyl methyl amine (0)> ethyldiisopropylamine (A), and triethylamine ( ) in hexane-ethyl acetate and ethyl acetate-acetonitrile mixed solvents. From ref. (114) with permission of the American Chemical Society. 

In nonpolar solvents exciplex emission can be seen. Electron-rich alkanes such as 2,3-dihydropyran quench the exciplex fluorescence and also the formation of the cycloadduct. Triethylamine behaves in a similar manner. 9-Cyanophenanthrene forms cycloadducts with styrenes (Caldwell and Smith,... 

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