Tertiary amines fluorescence

Recently/ the crosslinking reactions of tetrafiinctional epoxy resins with aromatic primary diamines was investigated. The crosslinked polymers were characterized by UV visible and fluo> rescence spectroscopies after gelation. The amount of tertiary amine fluorescence intensity of the spectra shows significant amounts of such amines in the finished products. The infrared spectra confirm the overall reaction of epoxides with amines, but also show that ether formation becomes significant only late in the cure. In addition, during the cure, especially in air, some oxidations and degradations occur. This results in color formation. 

This order agrees with that of quenching constant (Aqr) vaiues of the fluorescence of amines by AN. That is, the easier the reaction between an excited aromatic tertiary amine and the ground state AN, the faster the initiation. 

In 159 and 163-166 the tertiary amine function is coordinated to the boron atom and transmits the electronic change due to the ester formation to the chromophore. In 160-162 the boron atom is directly connected to the chromophore. After the complexation of the saccharide, the change of the charge transfer, e.g., for 159 [249-251], or the fluorescence bands, e.g., for 160-166 [252-255], can be measured and interpreted. The most selective binding of n-glucose has been achieved with host 164 that forms a 1 1 complex with a macrocyclic structure (Scheme 1). 

The blue derivatives formed with the reagent by alkaloids remain stable for at least one day and usually much longer (cover the chromatogram with a glass plate) [2, 6, 7]. The shade of color produced can be affected by fluorescence indicators incorporated in the silica gel layer [7]. Tertiary amine alkaloids do not react at room temperature with the acetaldehyde-containing reagent [2]. 

Dendritic hosts can be used in aqueous solution to encapsulate water-soluble fluorescent probes. Changes in the photophysical properties of these encapsulated probes are useful to understand the properties of the microenvironment created by the dendritic interior. For example, adamantyl-terminated poly(pro-pylene amine) dendrimers from the first to the fifth generation (36 represents the third generation) can be dissolved in water at pH<7 in the presence of -cyclodextrin because of encapsulation of the hydrophobic adamantyl residue inside the /1-cyclodextrin cavity and the presence of protonated tertiary amine units inside the dendrimer [72]. Under these experimental conditions, 8-anifi-... 

Refaat et al. [24] used a spectrophotometric method for the determination of primaquine, and 16 other tertiary amine drugs, in bulk or in pharmaceuticals. The method involved the condensation of malonic acid with acetic anhydride in the presence of a tertiary amine in an aliphatic or a heterocyclic system. The condensation product is highly fluorescent and allows the spectrofluorimetric determination of the drug in the ng/mL ranges (Xcx = 415 nm and >.em = 455 nm). 

The second chromophore involves another a,g-unsaturated ketone that is in conjugation with an anomalously behaving amide (7). The tertiary amine is responsible for the basic character and the phenolic group is acidic. CTC is fluorescent and can be assayed polarographically (8). 

A distinct advantage of PET sensors is the very large change in fluorescence intensity usually observed upon cation binding, so that the expressions off-on and on-off fluorescent sensors are often used. Another characteristic is the absence of shift of the fluorescence or excitation spectra, which precludes the possibility of intensity-ratio measurements at two wavelengths. Furthermore, PET often arises from a tertiary amine whose pH sensitivity may affect the response to cations. 

Photoinduced intramolecular interaction of t-S and tertiary amine moieties linked with a polymethylene chain has also been studied24. The photoexcitation of fraws-stilbene in which a tertiary amine is attached to the ortho position with a (CH2)i-3 linker leads to fluorescent exciplexes by intramolecular electron transfer, and results in no more than trans-cis isomerization. The failure to give adducts from the intramolecular exciplexes could arise from the unfavourable exciplex geometry to undergo the necessary bond formation. 

Whenever only primary amines need to be derivatized, fluorescamine often constitutes the reagent of choice. Fluorescamine, although nonfluorescent itself, can react with primary amines forming highly fluorescent pyrrolinones (139-144). Aliphatic primary amines favor derivatization reaction at pH 8-9, whereas primary aromatic amines exhibit optimal reactivity at pH 3-4. Secondary amines are also fully reactive with fluorescamine but their products do not fluoresce. However, secondary amines can be detected with fluorescamine if they are converted to primary amines by oxidation with N-chlorosuccinimide prior to their fluorescamine derivatization (145, 146). Alcohols can also interact with fluorescamine but this reaction is reversible as a result, alcohols just slow down the reaction rate of fluorescamine with primary amines. On the other hand, tertiary amines and guanidines are not reactive at all with fluorescamine. 

The fluorescence of 3-t (113-117) and 3-7 (118) is quenched by secondary and tertiary amines. Rate constants for quenching of It by tertiary amines increase with decreasing amine ionization or oxidation potential (Table 11), as expected for the formation of a charge-transfer stabilized exciplex in which the amine serves as the electron donor. Electron transfer quenching in nonpolar solvent is calculated to be exothermic for amines with E 2 < 1 34 V. Thus, it is not surprising that secondary and tertiary amines quench 3-t with rate constants which approach or even exceed the rate of diffusion. The inefficient quenching of It and 3-7 by primary amines is consistent with their higher oxidation potentials. 

The observation of decreased exciplex fluorescence intensity and increased adduct formation with increasing solvent polarity (Fig. 10) led to the proposal that adduct formation proceeds via initial one-electron transfer to yield a radical ion pair, followed by proton transfer to yield a 1,2-diphenylethyl and a-di-alkylaminoalkyl radical pair, which subsequently combines to yield 63, disproportionates or diffuses apart (114). Subsequent investigation of this reaction led to the proposal that proton transfer occurs only from the initially formed exciplex or contact radical ion pair prior to solvation to yield a solvent separated radical ion pair. The detailed mechanism for reaction of It with tertiary amines in acetonitrile solution is summarized in Fig. 11 (116c). 

The addition reactions of It with amines are also presumed to occur via exciplex or radical-ion pair intermediates however, exciplex fluorescence is observed only under conditions where chemical reactions do not occur. Transfer of hydrogen from the amine a-C-H (tertiary amine) or N-H (secondary amine) bond results in the formation of a radical pair which ultimately gives rise to stilbene amine adducts and other free-radical derived products. The radical-ion pairs can also be intercepted by external electrophiles and nucleophiles, leading to formation of radical-ion-derived products. 

The fluorescence quenching experiments of aromatic hydrocarbons by tertiary amines, including /V,/V-dialkylanilincs, in less polar solvents show the typical exciplex emissions [382-384], but products are not obtained or inefficiently produced. On the other hand, in polar solvents such as acetonitrile or methanol, the photoinduced electron transfer from the amines to Aril efficiently occurs to give the addition products. Interestingly, some primary and secondary aliphatic and aromatic amines caused the photoinduced electron transfer even in nonpolar solvents. 

The same mechanism accounts for the results obtained with 4-chlorobiphenyl390. The rate constants for quenching of the triplet states of 4-chlorobiphenyl and 1-chloronaph-thalene by various tertiary amines have been determined391. At an amine concentration of 2 x 1(T4 M ca 50% of the triplets of 4-chlorobiphenyl are quenched and ca 90% are quenched at a 10 3 M amine concentration. At this latter concentration very little fluorescence quenching occurs. Since dechlorination occurs at amine concentrations in the range of 10 3 to 10 4 M, it appears reasonable to invoke a reaction which occurs via the triplet state. 

---