Nitrobenzoxazoles and Nitrobenzoxadiazoles

It is interesting to note that 5-nitrobenzoxazole has two absorption maxima 224 (4.39) and 270 nm (3.84), while 6-nitrobenzoxazole shows only one maximum in area Amix 282 nm (4.01) [1200], A similar pattern is observed for 5-nitro- and 6-nitro-2-alkyl(aryl)benzoxazole too. The available experimental data are not enough to explain spectral differences of this kind. Apparently, it would be well to carry out quantum-chemical calculations or to involve other physical-chemical methods. An investigation of chromophoric 2-(4 -diphenyl)-5-nitrobenzoxazole with the help of UV (A 305 nm), fluorescence and laser spectroscopy has been reported by Chinese chemists [1201], Chromophores 2-(2 -hydroxy-4 -aminophenyl)-6-nitrobenzoxazole [ 1202], 2- [4-[4-(V,V-dihydroxyethyl-amino)-phenylazol]-phenyl -6-nitrobenzoxazole, 2-[4-(/V-mcthyl,V-hydroxyethyl-amino) 

In recent years nonlinear optical materials on the basis of nitroazoles, especially nitrobenzoxazoles and nitrobenzoxadiazoles, have investigated under intense scrutiny, at that and UV and fluorescence spectroscopy is widely used in studying of their structure and dynamics [1202-1225], 4-Aminosubstituted 7-nitrobenzofura-zans have a strong band in the visible region ( =457-483 nm) due to their chromophore properties [777]. 4-Substituted 7-nitrobenzofurazans possess a strong fluorescence that has led to their use as biochemical fluorescent probes in cell membranes [777, 1226-1228], 

A comprehensive research of a large number of benzofurazan nitro derivatives using UV spectroscopy and other physical-chemical methods has been carried out [777, 1006, 1007, 1106, 1107, 1229-1241], The frequencies of long-wave absorption bands of hydroxy- and aminosubstituted of nitrobenzofurazans greatly depend on the solvent nature [1106, 1107, 1230-1233, 1235, 1236], They are assigned to the bands of intramolecular charge transfer [1007, 1232], Correlation relationships between the wave number (v) and the Kamlet-Taft solvatochromic parameter (it ) are presented in the works cited  

The acid-base equilibrium constants of 3-oxy-7-nitrobenzofurazans were determined with the help of UV spectroscopy [1106, 1234], Kinetics of the reaction of methoxydegalogenization and hydrolysis of 4-chloro-7-nitro-2,l,3-benzoxadiazole has been investigated [1106], UV-spectra of some nitrobenzofurazan derivatives are described [1242-1244], 

UV-visible spectra of porphyrin systems obtained on the base 4-nitro-, 4-chloro-7-nitro-2,l,3-benzoxadiazoles or 4-nitro-2,l,3-benzoselenadiazole have been studied in detail [1241], 

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