Excited state dipole moments of N,N-dimethylaniline from thermochromic effect on electronic absorption and fluorescence spectra

The effect of temperature on absorption and fluorescence spectra of N,N-dimethylaniline (DMA) in ethyl acetate has been studied for temperature ranging from 293 to 388 K. The permittivity ε and refractive index n of the solvent decrease with temperature increase and the absorption and fluorescence bands are blue shifted (so-called “thermochromic shift”). Based on this phenomenon, the dipole moment μ_e in the excited singlet state and the Onsager interaction radius a for DMA were determined using the Bilot and Kawski theory [L. Bilot, A. Kawski, Z. Naturforsch. 17a (1962) 621; 18a (1963) 10, 256].

For the known dipole moment in the ground state μ_g = 1.61 D and for /a³ = 0.54 ( is the polarizability of the solute) the average value of μ_e = 3.55 D and a = 3.1 Å were determined. The obtained values for DMA are compared with the experimental values determined by other authors.     

The permanent electric dipole moments of iron monoxide, FeO

The Q(4) and R(4) branch features of the (0,0)D (5)Delta(4)-X (5)Delta(4) band system and the Q(3) and R(3) branch features of the (0,0)D (5)Delta(3)-X (5)Delta(3) band system of iron monoxide FeO have been studied by optical Stark spectroscopy. The Stark splittings in the high resolution laser induced fluorescence spectra were analyzed to produce values for the magnitude of the permanent electric dipole moments /mu/ of 4.50+/-0.03, 4.29+/-0.05, 2.53+/-0.04, and 2.58+/-0.06 D for the X (5)Delta(4) (nu=0), X (5)Delta(3) (nu=0), D (5)Delta(4) (nu=0), and D (5)Delta(3) (nu=0) states, respectively. The results are compared to several ab initio predictions and to FeC. The qualitative trends are explained in terms of a molecular orbital correlation picture.     

Effects of solvent on the electronic absorption and fluorescence spectra of quinazolines,and determination of their ground and excited singlet-state dipole moments

The electronic absorption, and fluorescence excitation and emission spectra of 11 quinazolines have been measured at room temperature (298 K) in several solvents of different polarities (cyclohexane, dioxane, ethylether, chloroform, ethylacetate, 1-butanol, 2-propanol, ethanol, methanol, acetonitrile, dimethylformamide and dimethyl sulfoxide). The effects of the solvent upon the spectral properties are discussed. Experimental ground-state dipole moments were measured for quinazolines and were used in combination with the spectral results to evaluate their first excited singlet-state dipole moments by means of the solvatochromic shift method. The theoretical ground and excited singlet-state dipole moments for selected quinazolines were calculated as a vector sum of the π-component (obtained by the PPP method) and the σ-component (obtained from σ-bond moments). A reasonable agreement was observed between the experimental and the theoretical values. Excited singlet-state dipole moments are higher than the ground-state values for most quinazolines.     

Electronic absorption and fluorescence spectra and excited singlet-state dipole moments of biologically important pyrimidines

Electronic absorption and fluorescence emission spectra of several biologically important pyrimidines were measured at room temperature (298 K) in the following solvents: dioxane, ethyl ether, chloroform, ethyl acetate, 1-butanol, 2-propanol, methanol, dimethylformamide, acetonitrile, and dimethyl sulfoxide. The compounds studied were uracil, thymine, cytosine, 5-fluorouracil, 5-chlorouracil, 5-bromouracil, 5-iodouracil, 2-thiouracil, barbituric acid, and orotic acid. In combination with the ground-state dipole moments of the above compounds, these spectral data were used to determine their lowest excited singlet-state dipole moments using the soivatochromic method. The effects of the solvent upon the spectral properties and of the structure upon the ground and excited singlet-state dipole moments are discussed. For most of the compounds, the excited singlet-state dipole moments are higher than their ground-state counterparts.The theoretical dipole moments for all the pyrimidines listed above, as well as for pyrimidine, alloxan, and uracil-5-carboxylic acid, were calculated by two methods. One approach involved a combination of the PPP (-LCI-SCF-MO) method for the -contribution to the overall dipole moment and the -contribution obtained as a vector sum of the -bond moments and group moments. The second set of theoretical values was obtained by the CNDO/2 method. The results were compared with the experimental dipole moments.Presented, in part, at the XIth IUPAC Symposium on Photochemistry, Lisbon, Portugal, July 27–August 1, 1986, and at the 192nd National Meeting of the American Chemical Society, Anaheim, CA, September 7–12, 1986. Part of this work was carried out at the University of Texas at El Paso, El Paso, TX, during the tenure of one of the authors there (C. P.). This paper is dedicated to Dr. Rudolf Zahradník, the teacher of one of the authors (C. P.) and the authors' friend and colleague.     

Calculation of the electronic structure and dipole moments of 4-substituted tetrabromopyridines

It is demonstrated from the results of a quantum-chemical calculation by the CNDO/2 (complete neglect of differential overlap/2) method and the experimental dipole moments for a number of 4-substituted tetrabromopyridines that the character of the intramolecular interactions in the investigated compounds differs little from that observed for 4-substituted nonhalogenated pyridines. A linear relationship between the charge on the heteroatom and the p constants for the substituents in the 4 position was observed. A similar relationship was obtained for the experimental dipole moments and the substituent constants.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 927–931, July, 1981.     

The polar nature of 2,1,3-benzoxadiazole, -benzothiadiazole, -benzoselenadiazole and derivatives as determined by their electric dipole moments

Permanent electric dipole moments have been determined in benzene solutions at 25° for the oxygen, sulfur, and selenium series of 2,1,3-benzodiazoles. The derivatives studied contained 4, 5, and 6 substituted methyl, chloro, nitro, and amino groups. The dipole moment data of the derivatives were analyzed relative to that of the parent species which allowed deductions to be made about the mesomeric structures operating in the compounds. The mesomeric charge transfer increases regularly from the oxygen to the selenium structures, being nearly undetected in 2,1,3-benzoxadiazole derivatives and very pronounced in the 2,1,3-benzoselenadiazoles.     

Vibrational spectra,dipole moments,and conformations of acylic sulfoxides

Conclusions Acyclic aliphatic and aliphatic-aromatic sulfoxides exist in the form of equilibrium mixtures of conformations. In the case of bromomethyl methyl sulfoxide, a conformational equilibrium of three forms is observed, and an equilibrium between two forms basically exists for chloromethyl methyl sulfoxide and halomethyl aryl sulfoxides.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2758–2764, December, 1980.We thank S. A. Katsyub for supplying the programs for the calculations of the frequencies and the normal modes of vibration.     

Geometrical derivatives of dipole moments and polarizabilities

Molecular dipole moments and polarizabilities, as well as their geometrical derivatives, are given analytical expressions for multiconfiguration self-consistent-field and configuration interaction wavefunctions. By considering the response of the electronic wavefunction induced by electric field and geometrical displacement terms in the Hamiltonian, the response of the total electronic energy to these terms is analyzed. The dipole moment and polarizability are then identified through the factors in the energy which are linear and quadratic in the electric field, respectively. Derivatives with respect to molecular deformation are obtained by identifying factors in these moments which are linear, quadratic, etc., in the distortion parameter. The analytical derivative expressions obtained here are compared to those which arise through finite-difference calculations, and it is shown how previous configuration-interaction-based finite difference dipole moment and polarizability derivatives are wrong. The proper means of treating such derivatives are detailed.     

Photoelectron spectra and electronic structure of aza-boron-dipyridomethene derivatives

The electronic structure of three aza-boron-dipyridomethene derivatives containing different hydrocarbon groups at the boron atom is studied by ultraviolet photoelectron spectroscopy and calculations at the density functional theory level. According to the experimental and theoretical data, the higher occupied molecular orbitals of anthracene, acridine, and the studied complexes are of the same character. For the three studied compounds, the effect of alkyl and phenyl substituents on the electronic structure is determined. The parameters of the electronic structure of aza-boron-dipyridomethene (phenyl groups at the boron atom) and its β-diketonate analogue are compared. It is shown that in an energy range up to 11 eV the calculated results correlate with the ultraviolet photoelectron spectra.     

Schiff base compounds derived from (R)-3-phenyl-2-phthalimidopropionic acid: photochromism, solvatochromism, and fluorescence

The photochromic behaviors of four Schiff bases derived from (R)-3-phenyl-2-phthalimidopropionic acid were studied to reveal the substituent effect on the photosensitivity. Upon ultraviolet light radiation, all of compounds 1–4 exhibit photochromic behavior in solution through intramolecular hydrogen atom transfer. In solid state, only compound 2 is photochromic, which may be due to the presence of meta-site methoxyl. In solution, the photochromic behavior of compound 3 is remarkable than the other compounds, which may be ascribed to the presence of para-site hydroxyl. Only compound 4 exhibits solvatochromism, which may be ascribed to the large dissociation tendency of the naphthol hydroxyl. The influences of acidity on the UV–Vis absorption spectra of the title compounds were also studied.     

Synthesis,characterization and spectroscopic investigation of a novel phenylhydrazone Schiff base with solvatochromism

A novel Schiff base of 4,5-diazafluorene-9-p-nitrophenylhydrazone (DAFND) has been synthesized and characterized. The crystal structures of DAFND and its analogue 4,5-diazafluorene-9-phenylhydrazone (DAFPD) were determined by single crystal X-ray diffraction method. X-ray analyses reveal that DAFPD comprise of a nonplanar molecule and all atoms of DAFND are essentially coplanar. The color of DAFND changes from brown to blue when heated, so called thermochromism and the spectroscopic properties of the two compounds are investigated by electronic absorption spectra, showing DAFND possess solvatochromism, while DAFPD does not have thermochromic and solvatochromic properties. The λ_max of DAFND within various pure solvents are different ranging from 370 nm in toluene to 614 nm in pyridine. The imaginable mechanisms of thermochromism and solvatochromism are proposed.     

Ratiometric fluorescence and colorimetric sensing of anion utilizing simple Schiff base derivatives

Two ratiometric fluorescence and colorimetric anion sensors were designed and synthesized according to simple Schiff base reaction. Two compounds 1 and 2 were characterized by ESI–MS, elemental analyses and ¹H NMR. The sensors could give fast and visible color changes from yellow to red upon presence of the strong basic anions such as acetate ion. In particular, two compounds exhibited marked blue shifts (about 136 nm) in their emission spectra, when interacting with anions. Accordingly, the compounds 1 and 2 could act as real-time ratiometric fluorescence and colorimetric sensors for anions.     

Synthesis, characteristic and theoretical investigation of the structure, electronic properties and second-order nonlinearity of salicylaldehyde Schiff base and their derivatives

A series of asymmetric donor-acceptor substituted salen-type Schiff-bases have been synthesized and their structures, electronic properties and second order nonlinearities were investigated by DFT methods. In order to verify the stable of these Schiff-base derivates, the IR spectrum of these Schiff-base derivates were calculated, the result showed that these compounds are stable. The results of TD-DFT calculation indicate that the derivatives with the electron-donating group (CH3, OCH3 or N(C2H5)2) have a red shift absorption compared to derivatives with the electron-withdrawing group (NO2). The analysis of MOS indicates that the CN group has contribution to the LUMO orbital while the groups of OCH3, N(C2H5)2 and NO2 have contribution to the HOMO orbital. OCH3, N(C2H5)2 as electron rich groups, made the derivates have a larger first static hyperpolarizability. However, the compound (II) with a NO2 substituent, also has a large first static hyperpolarizability. This is probably because of the special transition model, namely the values of two oscillator strength f (fHOMO-1-LUMO=0.405, fHOMO-LUMO=0.321) are almost equal. In order to understand the influence of the energy gap (ΔE) between the HOMO and the LUMO orbitals on the first static hyperpolarizability, we calculated the energy gap (ΔE) of all Schiff-base compounds. The results show that the smaller the HOMO-LUMO energy gap is, the larger the first static hyperpolarizability is.     

Synthesis of new cyclotriphosphazene derivatives bearing Schiff bases and their thermal and absorbance properties

In this study, a series of cyclotriphosphazene derivatives containing a Schiff base (3a–3d) were synthesized by the reactions of hexachlorocyclotriphosphazene (1) with bis-aryl Schiff bases ( 2a – 2d ) having different terminal groups (H, F, Cl, and Br). The products ( 3a – 3d ) were characterized by elemental and mass analyses, FT-IR, and ¹ H, ¹³ C, and ³¹ P NMR spectroscopies. Furthermore, the structure of compound 3a was also determined by X-ray crystallography. The thermal behaviors and the spectral properties of the new cyclotriphosphazene compounds ( 3a – 3d ) were investigated and the results were compared in the series.     

A new method for estimating excited state dipole moments of molecules from the solvent effect on their electronic spectra

Some comments are made on the paper entitled “Excited state dipole moments of some monosubstituted benzenes from the solvent effect on electronic absorption spectra” by Prabhumirashi et al. (Spectrochim. Acta 39A, 663,1983) and a new method, which has been tested on some molecules and found satisfactory, is suggested for estimating the excited state dipole moment of molecules from the solvent effect on their electronic spectra.     

Photoelectron spectra and electronic structure of derivatives of imidazoline

We have obtained for the first time the photoelectron spectra (PES) of 20 diamagnetic and paramagnetic derivatives of imidazole. On the basis of calculations in the MNDO approximation, analysis of the vibrational structure, and comparisons in a series we have interpreted the bands in the range 7–11 eV. In the nitroxyl radicals of 3-imidazoline the highest occupied molecular orbital is the _NO ^* orbital, having also a contribution on the C⁴ atom. On introducing N-oxide groups there is a considerable rearrangement of the electronic structure of the radicals. In the PES of the nitroxyl radicals of 3-imidazoline-3-oxide there is multiplet splitting of the ionization band of the n_o·MO, amounting to 0.3–0.4 eV. Replacement of the methyl groups on the C² atom by methoxyl groups leads to an increase in the interactions of the unshared pairs of the O atoms of the nitronium and nitroxyl groups, while the same replacement on the C⁵ atoms leads to a considerable decrease in this interaction. When the substituent on the N¹ atom in derivatives of 3-imidazoline-3-oxide is varied the energy of ionization of the _C-NO MO decreases in the series: CH₃ < H OH < O < NO.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1769–1777, August, 1990.