Acridone, excited

Siegmund M, Bendig J (1980) The solvent dependence of the electronic spectra and the change of the properties of N-substituted acridones at electronic excitation (In German). 

Other chemiluminescent reactions yielding excited N-methyl acridone... 

Deveaux et al. [21] explained the fluorescent reaction of mefenamic acid by the formation of a substituted acridone after dissolving mefenamic acid in concentrated H2S04 and heating for 10 min at 100°C. The acridone exhibits an intense green fluorescence when excited by white light, and blue when excited by ultraviolet light. 

All data obtained with Tecan Ultra Evolution MTP reader. The following excitation and emission wavelengths were used EDANS and AMC 350 and 500 nm RhllO 485 and 535 nm TAMRA 535 and 595 nm PT14 405 and 450 nm. 4 = primary cleavage site confirmed by MS. AMC = aminomethylcoumarin. RhllO = rhodamine 110. yE = glutamic acid attached to RhllO via its carbonic acid in side chain. EDANS = fluorophore 5-[(2-aminoethyl)amino]naphthalene-l-sulphonic acid. DABCYL = 4-(4-dimethylaminophenylazo)benzoic acid quencher. BTN = biotin. PT14 = acridone-based fluorescence lifetime label. 

Fig. 3. The fluorescence excitation spectrum of acridone. Coverage 0.01 mg/g. — on SG200V,—on SG200A, ethanol,—in 18N sulfuric acid.

The fluorescence excitation spectrum of acridine in O.IN sulfuric acid has a band characteristic of acridinium cation at about 25000 cm, but on the other hand, acridine in ethanol has no band below 25000 cm" (see Fig. 8). The fluorescence excitation spectra of acridine both on SG200V and SG200A have a band near 25000 cra . These findings indicate that a proton is transferred to acridone from silanol groups in its ground state as a result of adsorption on the silica gel surface. The emission of acridine adsorbed on silica gel are reasonably assigned to the protonated species of acridine. 

The electron in the high-energy SOMO of the radical anion 8.220 (effectively the n orbital of the carbonyl group) is evidently transferred to the relatively low-energy LUMO of the acridone (Fig. 8.14), giving the product with the orbital occupancy of the n-it excited state, which simply emits a photon when the excited state 8.222 decays to the ground state. 

Lahri has reviewed the determination of acidity constants in excited singlet states as well as providing an extensive compilation of pK data. Schulman, Vogt, and Lovell have measured rate constants for the protonation of the excited base and deprotonation of the weak base acridone by fluorimetric titrations in moderately concentrated acid media using bromide ion as a quencher. 

The direct electronic excitation of lanthanide ions is very inefficient because of their low absorption coefficients and the occurrence of nonradiative deactivation processes mediated by solvent molecules, particularly by water. Therefore, sensitizing ligands are applied. These sensitizers are often termed as anterma chromo-phores. By using antenna chromophores like acridone or diaiyl ketones, the excitation wavelength for europium complexes, which is usually <370 nm, can be shifted to the visible region [5-7]. 

For this work we chose groups which could be excited to the triplet state easily. One was the carbazole moiety. The second was acridone. Both have acidic NH groups which can be used to attach them to the appropriate side chain. 

As can be seen in Figure 32.1b, lucigenin forms an unstable dioxetane, which decomposes to N-methylacridone in an electronically excited state. The excited acridone molecule emits light as it relaxes to a stable state. 

Fluorescence of acridone derivatives (106) from their excited singlet states was observed as thermochemiluminescence by thermal... 

Much of the evidence for this route came from the initially surprising oberservation that acridine 9-carboxylic acid hydrazide gave not the excited carboxylate, but emission from acridone. Strong support for the acyl anion route is obtained from the fact that 9-formyl acridine in strong base is highly chemiluminescent [80]. 

The formation of excited acridone can be explained by one of three mechanisms ... 

Nonetheless, a dioxetan decomposition mechanism for lucigenin chemiluminescence, based on the exergonic processes described in Chap. V, seems well established [3]. A direct demonstration of the intermediacy of this dioxetane was first made [4] in 1969 by treating 10,10 -dimethyl-9,9 -biacrylidene (4) with singlet oxygen from several sources. Emission from N-methyl acridone was unequivocally shown. The lifetime of the intermediate was characteristic of the supposed dioxetane. Intramolecular electron transfer has been suggested as the excitation mechanism in the decomposition of this and other electron-rich dioxetans. 

It is assumed that the primary excited N>methyl acridone is solubilized in the micelle. Thus energy transfer to other acridine derivatives, present in the alkaline solution, is inhibited. The N-methyl acridone spectrum is visible in the lucigenin chemiluminescence emission when CTAB is present, relatively unaffected by the more usual accompanying green emission. 

Dioxetans of this type can be made still more stable by the introduction of bulky substituents. The adamantyl derivative (26) can be easily crystallised [40], since it has a distinctly higher activation energy for decomposition (110.5 kJ mol as against 82.7 kJ moT ). The yield of excited singlet N-methyl acridone is 12%. 

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