Solvatochromic behavior of the electronic absorption spectra of some azo derivatives of amino pyridines

The electronic absorption spectra of a series of the entitled eight compounds containing groups with variable electronic characters were recorded. The solvents were selected to cover a wide range of parameters (refractive index, dielectric constant and hydrogen bonding capacity). The electronic transitions are assigned and the solvent induced spectral shifts have been analyzed in relation to the different solute-solvent interaction mechanisms using computational chemistry. The regression analysis is applied for correlation parameters. The phenomenon of tautomerism is explained. The electronic character of the substituent as well as the chemistry of the solvent are the major factors for the solvatochromic behavior.     

Electronic absorption spectra of some benzenechromiumtricarbonyl derivatives

Absorption spectra of some arenechromiumtricarbonyl derivatives have been studied. The linear dependence of the extinction coefficient of the longer wavelength absorption band on σ_p⁺ constants of substituents in a benzene ring has been established and it has been shown that a longer wavelength band is a band of intramolecular charge transfer from the central chromium atom to π-bonded arene.     

Electronic absorption spectra of some arylidene pyrazolone derivatives

The u.v. and visible spectra of some 1 - phenyl - 3 - methyl - 4 - arylidene - 2 - pyrazolin - 5 - one derivatives are investigated in pure and mixed organic solvents as well as in aqueous buffer solutions. Electronic transitions have been identified as either locally excited or predominantly charge transfer states. Moreover, the spectra of the hydroxy derivatives in proton acceptor solvents (DMF, DMSO, ethanol) are characterized by an extra band located at longer wavelengths, which is ascribed to an intermolecular CT transition. This involves an electron transfer from the lone pair of electrons of the oxygen atom of the solvent molecules (ψ_ol) to the antibonding orbital of the substituent OH group. The spectral shifts are discussed in terms of medium effects and in relation to molecular structure. The variation of absorbance with pH is utilized for the determination of pK_a for the dimethylamino and hydroxy derivatives.     

Effect of solvents on the electronic absorption spectra of some substituted diarylformazans

Summary The electronic absorption spectra of some substituted diarylformazans in organic solvents of varying polarities are studied. The absorption bands are assigned to the corresponding electronic transitions in the molecules. The solvent effects on the intramolecular charge transfer bands are discussed using various solvent parameters. The charge transfer nature of the bands was also confirmed by the solvent effects on the absorption spectra of some formazans. Molecular orbital calculations using MNDO-PM3 were performed and indicate atrans configuration as the favoured geometry.

---

Lösungsmitteleinflüsse auf die Absorptionsspektren einiger substituierter Diarylformazane

Zusammenfassung Die Absorptionsspektren einiger substituierter Diarylformazane werden in organischen Lösungsmitteln unterschiedlicher Polarität untersucht. Die Absorptionsbanden werden den entsprechenden Elekronenübergängen in den Molekülen zugeordnet. Die Lösungsmitteleffekte auf die intramolekularencharge-transfer-Banden werden unter Verwendung verschiedener Lösungsmittelparameter diskutiert. Diecharge-transfer-Natur der Banden wurde durch den Einfluß der Lösungsmittel auf die Absorptionsspektren einiger Formazane bestätigt. MO-Rechnungen (MNDO-PM3) wurden durchgeführt und bestätigen einetrans-Konfiguration als bevorzugte Geometrie.

     

Vibrational and electronic absorption spectra of some trisubstituted benzenes

Despite our studies on the Π* ← Π systems in some trisubstituted benzenes, the available data are limited, especially concerning two heavy and one light or one heavy and two light substituents. We therefore report and interpret the vapour phase electronic absorption, infrared and Raman spectra of 1-bromo-2,4-difluoro-, 1-bromo-3,4-difluoro-, 1-bromo-3,5-difluoro-, 1,3-dichloro-2-fluoro- and 1,3-dichloro-4-fluoro-benzenes.     

Infrared and electronic absorption spectra of some trisubstituted benzenes

The electronic absorption spectra of 2,3-, 2,4-, 2,5-, 2,6- and 3,4-difluorobenzonitriles, 3,4-difluoroaniline and 3,4-difluoroanisole in the ultraviolet region in vapour phase have been recorded on medium quartz and Hilger large quartz spectrographs and on a Hitachi model 150-20 UV-VIS ratio recording spectrophotometer. All the molecules investigated have exhibited two π* ← π band systems corresponding to ¹B_2u ← ¹A_1g (λ2600 Å) and ¹B_1u ← ¹A_1g (λ2100 Å) systems of benzene. The infrared absorption spectra of all the molecules studied have also been recorded and analysed. These infrared data have been taken to help analyse the u.v. spectra of the molecules studied.     

Ultraviolet absorption spectra of some pyridine and nicotine derivatives

Summary Comparison of the ultraviolet spectra of nicotine, N-methylanabasine, and their N-oxides shows that though the characters of the absorption of compounds containing the N-oxide group in the aromatic part of the molecule, on the one hand, and in the hydrogenated part, do not differ considerably, they are nevertheless sufficiently specific for a clear distinction to be drawn.For Communication 3 see [1].     

pH-induced changes in electronic absorption and fluorescence spectra of phenazine derivatives

The visible electronic absorption and fluorescence spectra as well as fluorescence polarization degrees of imidazo-[4,5-d]-phenazine (F1), 2-methylimidazo-[4,5-d]-phenazine (F2), 2-trifluoridemethylimidazo-[4,5-d]-phenazine (F3), 1,2,3-triazole-[4,5-d]-phenazine (F4) and their glycosides, imidazo-[4,5-d]-phenazine-N1-beta-D-ribofuranoside (F1rib), 1,2,3-triazole-[4,5-d]-phenazine-N1-beta-D-glucopyranoside (F4gl), were investigated in aqueous buffered solutions over the pH range of 0-12, where the spectral transformations were found to be reversible. The effects of protonation and deprotonation on spectral properties of these dyes were studied. We have determined the ranges of pH, where individual ionic species are predominant. In aqueous buffered solutions the fluorescence was found only for neutral species of F1, F1rib, F2, and F4gl dyes, whereas for the ionic forms of these dyes, as well as for F3 and F4 ones, the fluorescence has not been detected. The concentrational deprotonation pKa values were evaluated from experimental data. It was shown that donor-acceptor properties of the substituent group in the second position of the pentagonal ring substantially affect the values of the deprotonation constants and the character of protonation for chromophore. The substitution of a hydrogen atom in the NH-group by the sugar residue blocks the formation of the anionic species, and results in enhancement of the dye emission intensity. The steep emission dependence for F1 and F1rib over pH range of 0-7 with intensities ratio of IpH 7/IpH 1=60 allows us to propose them as possible indicator dyes in luminescence based pH sensors for investigation of processes accompanied by acidification, e.g. as gastric pH-sensors. A comparative analysis of the studied dyes has shown that F4gl is the most promising compound to be used as a fluorescent probe for investigation of molecular hybridization of nucleic acids.     

Experimental and quantum chemical studies of the electronic absorption spectra of pyrimidine derivatives

The electronic absorption spectra of different pyrimidine derivatives have been measured experimentally and calculated theoretically by the PPP and CNDO/S methods. These pyrimidine derivatives are: 4,6-dichloro-pyrimidine (I), 4,6-dichloro, 5-amino-pyrimidine (II), 2,4,6-trichloro-pyrimidine (III), 4,6-dihxdroxy-pyrimidine (IV), 4,6-dihxdroxy-5-nitro-pyrimidine (V), 2,4-diamino-pyrimidine (VI), 2,4-diamino-6-hydroxy-pyrimidine (VII), 2,4-dihydroxy-5-carboxy-pyrimidine (VIII), 2,4-dimethyl-6-hydroxy-pyrimidine (IX), 5-nitro-uracil (X), and orotic acid (XI). The observed electronic spectral shifts are quantitatively analyzed in relation to different solute–solvent interaction mechanisms. The effects of solvent polarity and hydrogen bonding on the spectra are discussed in the light of theoretical predictions. This comparative analysis provides a reasonable picture of the solvent effects on the absorption spectral properties of pyrimidine nucleobases.     

The electronic absorption spectra of some acyl azides molecular orbital treatment

The electronic absorption spectra of benzoyl azide and its derivatives: p-methyl, p-methoxy, p-chloro and p-nitrobenzoyl azide were investigated in different solvents. The observed spectra differ basically from the electronic spectra of aryl azides or alkyl azides. Four intense pi-pi* transitions were observed in the accessible UV region of the spectrum of each of the studied compounds. The contribution of charge transfer configurations to the observed transitions is rather weak. Shift of band maximum with solvent polarity is minute. On the other hand, band intensity is highly dependent on the solvent used. The observed transitions are delocalized rather than localized ones as in the case with aryl and alkyl azides. The attachment of the CO group to the azide group in acyl azides has a significant effect on the electronic structure of the molecule. The arrangements as well as energies of the molecular orbitals are different in acyl azides from those in aryl azides. The first electronic transition in phenyl azide is at 276 nm, whereas that of bezoyle azide is at 251 nm. Ab initio molecular orbital calculations using both RHF/6-311G* and B3LYP/6-31+G* levels were carried out on the ground states of the studied compounds. The wave functions of the excited states were calculated using the CIS and the AM1-CI procedures.     

Infrared absorption spectra of some derivatives of 1,2,3,4-tetrahydro-Β-carboline

The IR absorption spectra in 3800-1400 cm^–1 region of 1-propyl-, 1-carboxy-, 1-carboxy-1-methyl-, and 1-benzyl-1-carboxy-6-hydroxy-1,-tetrahydro--carbolines, their O-methyl derivatives, and their hydrochlorides are discussed. An assignment of the bands due to the stretching vibrations of NH, NH ₂ ⁺ , OH, COO^–, and COOH groups is proposed. The hypothesis has been put forward that strong intermolecular and intramolecular hydrogen bonds exist in the substances studied.Translated from Khimiya Geterotsiklicheskikh Soedinenii, Vol. 6, No. 6, pp. 775–778, June, 1970.     

Solvent effects on the electronic absorption spectra and acid strength of some substituted pyridinols.

The electronic absorption spectra of some substituted pyridinols in organic solvents of different polarities are studied. Also, the solvent effects on the intramolecular charge transfer bands are discussed using various solvent parameters. The acid-base equilibria of the compounds used are studied spectrophotometrically in various mixed aqueous solvents at 25 degrees C and 0.1 M ionic strength (NaClO4). Furthermore, the influence of the solvents on the dissociation constants and tautomeric equilibria of a pyridinol derivatives are discussed. The effect of molecular structure of the pyridinols on the pK's is also examined.     

An experimental and theoretical study of the electronic absorption spectra of 3-hydroxypyridine derivatives

Theoretical and Experimental Chemistry -     

The effect of solvents on the electronic absorption spectra of mesoionic 1,8,4 thiadiazolium-2-thiolate derivatives

The electronic absorption spectra of 4,5-diphenyl-, 4-pheriyl-5-(4-fluorophenyl)-, 4-phenyl-5-(4-chlorophenyI)-, and 4-phenyl-.5-methyl-1,3,4-lhiadiazolium-2-thiolates have been measured in twenty-one pure solvents, aqueous ethanol and acetone solutions and cyclohexane-chloroform mixtures. They were found to exhibit three characteristic absorption bands; the first in the range 330-440 nm, the second at 260-280 run and the third near 200 ran. The first band was assigned to n → π* transition whereas the other two bands were assigned to π →π* transition. The n → π* transition band was found to be very sensitive, and the polarity of solvents, and some correlations between well-known solvent polarity parameters and the transition energies of these compounds have been presented.     

Nature of electronic transitions in absorption spectra of phenyl derivatives of 1,3,4-sym-triazole

The electronic absorption spectra of 1,3,4-sym-triazole and its monophenyl, diphenyl, and triphenyl derivatives have been calculated in the -electron approximation by the PPP CI method. On the basis of special quantumchemical excitation indexes, transitions can be classified as either local or overall-molecular. For the latter, the dependence of properties on the structure of the -system was investigated.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 29, No. 2, pp. 169–173, March–April, 1993.     

Syntheses and electronic absorption spectra of some new penta- and di-methine cyanine dyes

The reaction of a ratio of 1 mole of 5-chloro-3-methyl-1-phenyl pyrazolo-4[2(4)]-dimethine cyanine ( 1a,b ) or (5-chloro-4-formyl-3-methyl-1-phenylpyrazole) 2 with 2 moles of an appropriate 2(4)-heterocyclic quaternary salt afforded the novel pentamethine cyanine dyes ( 3a–3e ). Other reactions of 2 with heterocyclic nitrogen bases, followed by condensation of the newly formed quaternary nitrogen salts ( 4a–4c ) with methoheterocyclic iodide salts provided the corresponding unsymmetrical dimethine cyanine dyes ( 5a–5g ). The new pentamethine and dimethine cyanine dyes were identified by elemental analyses and IR and ¹H-NMR spectral data. The visible absorption spectra of some selected dyes were investigated in pure and mixed solvents as well as in universal buffer solutions. The measure of the variation of absorbance with pH was utilized for the determination of the pK_a values for compounds 3b, 3d, 3e, 5e , and 5f , and these data are discussed. © 1997 John Wiley & Sons, Inc. Heteroatom Chem 8 : 259–266, 1997.     

Studies on mesoionic compounds,II. The solvent effect on the electronic absorption spectra of mesoionic 2,3-diaryl-2H-tetrazolium-5-thiolate derivatives

The electronic absorption spectra of 2,3-di(2-fluorophenyl)-, 2,3-di(4-fluorophenyl)-, 2,3-di-(2-chlorophenyl)-, 2,3-di(2-methylphenyl)-, 2,3-di(4-methylphenyl)- and 2,3-di(2-methoxyphenyl)-2H-tetrazolium-5-thiolates have been measured in pure and mixed solvents. They were found to exhibit three characteristic absorption bands at 480-380 nm, near 250 and near 210; the longest wavenlength band of which was assigned to an n → π* transition.