3-aminophthalate fluorescence

However, the formation of these products does not appear to play a critical role in the decision as to whether the 425 nm and 480 nm maxima are due to different states of the same molecule or to different compounds. It was reported that special care was taken to ensure the purity of luminol and of 3-aminophthalate 109>. In commercially available 3-amino-phthalic acid a yellowish impurity exhibiting brilliant green fluorescence was detected 109> this substance also formed in neutral solutions of pure 3-amino phthalic acid and crystallized from these solutions in yellow crystals. The structure of this substance was determined to be 53 its absorption spectrum has a maximum at 388 nm the fluorescence maximum is at 475 nm, with a fluorescence quantum yield of about 0.75 in DMF i 9). 

Albrecht [10] was the first to report the CL of luminol (5-amino-2,3-dihydro-1,4-phthalazinedione), in 1928. The chemiluminescent reaction involves the oxidation of luminol (usually by H202) and often occurs in the presence of a catalyst (or co-oxidant) such as Fc(CN)6 3, Cu(II), or Co(II)) (Fig. 2). The light emission, which is blue in water and yellow-green in DMSO, is identical with the fluorescence of the 3-aminophthalate oxidation product [11],... 

The emitting species was found to be the singlet-excited state of 3-aminophthlate ion in both protic and aprotic solvents. This identification was made based on the equivalence of the chemiluminescence spectrum of luminol and the fluorescence spectrum of 3-AP ion . In different reaction media, slightly different maximum chemiluminescence wavelengths are observed (Table 2). The spectral shift observed when the system changes from aqueous media to DMSO or other aprotic solvents can be ascribed to a quinoidal form of 3-aminophthalate (26) formed in aprotic solvents (Scheme 15). ... 

TABLE 2. Chemiluminescence maxima of luminol and fluorescence maxima of 3-aminophthalate (F13 ap) ... 

Firstly, in order to obtain an understanding of the mechanism of the sensitized luminol-based CL reaction, the CL emission spectrum was obtained with a F-4500 fluorescence spectrophotometer. The results showed the maximum emission wavelength in the presence of ofloxacin was the same as that in the absence of ofloxacin and the maximum light emission was at about 425 nm. The emitter was 3-aminophthalate, the oxidation product of luminol. 

R = /j 2-perylene (White and Brundrett, 1973), R = 6-N-(.3-amino-2-hydroxypropyl)amino and R = z-phenyl-3(4-amino-butyl)- /-ethyl amino (Schroeder et dl., 1978) gives higher values of 4> than Luminol (I) (R = 5-amino). Since the fluorescence yield of the aminophthalic acid product (II), = 0.3... 

The identity of the emitting species has been confirmed by the coincidence of the chemiluminescence and fluorescence spectra of 3-aminophthalate. There is, however, an observed red shift in the luminescent emissions between solvents such as water (2n,ax 420 nm) and dimethylsulfoxide (An,ax 500n )- The change from blue to yellowish-green chemiluminescence can be explained in terms of a rapid tautomer-ism of the emitting species in the aprotic solvent prior to photon ejection (Scheme 5). 

Although the nature of the peroxide is still debatable, the remainder of the reaction is well understood. The chemical products of the reaction have been shown to be the 3-aminophthalate dianion and molecular nitrogen. The intermediate that emits light has been identified definitely as the excited state singlet of the 3-aminophthalate dianion. Thus, the fluorescence emission spectrum of the 3-aminophthalate dianion (produced by photon absorption) is identical to the spectrum of the light emitted from the chemiluminescent reaction. However, for numerous complicated reasons, it is believed that the... 

An extensive analysis of absorption, fluorescent, and chemiluminescent spectra has been cariied out by van dor Burg (183a) with dimethyldiacri-dylium nitrate, methylacridon, aminophthalic hydrazide and several derivatives, and pyromellitic acid hydrazide. Substituent groups in amino-... 

Changes in pH affect several properties. One of the most important is the fluorescence efficiency of the product dicarboxylate. The most thoroughly investigated compound 3-aminophthalate (p. 82) has its maximum fluorescence yield at pH 11-11.4 (cf. p. 84). Dialkylamino-substituted phthalic or naphthalene dicarboxylic acid dianions reach their maximum fluorescence yield at a somewhat higher pH [8]. 

The 9,10-diphenyl anthracene derivative (3) gives only about a third of the luminol chemiluminescence efficiency, although the corresponding dicarboxylate of (3) has a fluorescence quantum yield of about 0.8, compared with a 0p of 0.5 for 3-aminophthalate [16]. This result, however, was obtained for the DMSO... 

A strong influence is exerted by the base used in the chemiluminescent oxidation. It was observed [38-40] that only when quaternary ammonium hydroxides are used as base in the luminol reaction does there exist a one-to-one correlation between luminol chemiluminescence and aminophthalate fluorescence. With alkah metal hydroxides (NaOH, KOH) in DMSO, containing 10% water, the 425 nm maximum is more pronounced in 3-aminophthalate fluorescence than in luminol chemiluminescence. 

Some discrepancies between the fluorescence spectrum of 3-aminophthalic acid and the luminol chemiluminescence spectrum are at least in part due to reabsorption of the shorter-wavelength emission by luminol monoanion [30]. 

The chemiluminescence of luminol is a direct chemiluminescence, i.e. the reaction product aminophthalate is the primary excited species. A series of compounds has been synthesized since 1967 in which the energy-generating hydrazide group and the light emitting group (a fluorescent residue) are separated [5, 36-38]. 

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