Photophysical behaviour of 2,6-diaminoanthraquinone in different solvents and at various pH

The absorption and fluorescence spectral properties of 2,6-diaminoanthraquinone (DAAQ) have been investigated in a series of organic solvents of different polarity and in aqueous solutions with H o/pH/H_ in the range -10 to 17. The Stokes shift of DAAQ is correlated with various polarity scales. The study reveals the fluorescence of DAAQ dication is red shifted on protonation. The abnormal fluorescence of DAAQ dication is found to be due to large solvent relaxation in polar medium. The acidity constants for various prototropic reactions in S o and S1 states are determined and discussed.     

Quadrupolar solvatochromism: 4-amino-phthalimide in toluene

We present calculations of the temperature dependence of the solvent reorganization energy of 4-amino-phthalimide chromophore in quadrupolar toluene. The reorganization energy is a sum of the contributions from quadrupolar and induction solvation. We employ several calculation formalisms in order to evaluate their performance against the experiment. The point-dipole and full atomic distributions of solute charge are compared to show that the point-dipole approximation works well for this chromophore. We also show that most of the reorganization entropy comes from the quadrupolar response. Induction solvation amounts to about 10% of the entropy. Both the reorganization energy and the reorganization entropy are greatly affected by the local solute-solvent density profile (density reorganization) which contributes about half of their values. The induction reorganization energy is strongly affected by the microscopic, nonlocal nature of the density fluctuations of the solvent around the solute.     

Pronounced solvatochromism of charge-transfer complexes in strongly hydrogen bonding solvents

A large bathochromic shift is reported for the charge-transfer (CT) transition in complexes of π-electron donors with electron acceptors containing CO groups in strongly H-bonding solvents such as trifluoroacetic acid and hexafluoroisopropanol. The results of ¹³C-NMR measurements and SCF-LCAOMO calculations indicate that this effect can be attributed to an increased electronegativity of the acceptor upon hydrogen bond formation with the solvent.     

Photophysical studies of Merocyanine 540 dye in aqueous micellar dispersions of different surfactants and in different solvents

The fluorescence spectra of Merocyanine 540 (MC 540), an anionic dye have been studied in aqueous solution of different nonionic surfactants. The results show the enhancement and red shift of fluorescence bands, indicating electron transfer from the surfactants to the excited dye. This is also supported by the photovoltage generation by the dye-surfactant systems in a photoelectrochemical cell. Possible mechanisms of the excited state interaction and photovoltage generation have been suggested. From the thermodynamic, spectrophotometric and photogalvanic results, it can be concluded that the electron donating abilities of the nonionic surfactants towards MC 540 are in the order: Tween 80 approximately Tween 60>Tween 40>Tween 20>Triton X-100. The spectral studies (both absorption and fluorescence) of Merocyanine 540 have been carried out in solvents of varying polarities as well as in an aqueous micellar dispersions of nonionic surfactants. The Stokes shifts of the fluorescence from the absorption have been found to increase with increasing polarity of the solvents. An attempt has been made to ascertain the polarity of the microenvironment of Merocyanine 540 in the nonionic surfactant media from the photophysical characteristics of the dye in different solvents of known polarities.     

Photophysical properties of a 1,2,3,4,5,6-hexasubstituted fullerene derivative

The photophysical properties of a novel 1,2,3,4,5,6-hexasubstituted fullerene derivative (1) are examined in this study. In addition to the ground state absorption spectrum of 1, we report its triplet-triplet absorption spectrum and molar extinction coefficient (Deltae(T-T)), as well as the triplet quantum yield (PhiT), lifetime (tauT), and energy (ET). The saturation of a single six-member ring on the fullerene cage results in significant changes in the triplet state properties as compared to that of pristine C60. The triplet-triplet absorption spectrum shows a hypsochromic shift in long wavelength absorption, and both the triplet state lifetime and the triplet quantum yield are decreased. The triplet energy was found to be similar to that of C60. In addition, the quantum yield (PHI(delta)) of singlet oxygen generated by 1 was calculated and is found to be significantly less than in the case of C60.     

A bicyclic cispentacin derivative as a novel reverse turn inducer in a GnRH mimetic

A cispentacin-derived bicyclic beta-amino acid (Bic) has been synthesized and incorporated into the 6-position of GnRH. The new GnRH analogue has been characterized with respect to its structure in solution and its activity and affinity toward the human GnRH receptor.     

Photophysical processes of a fluorene derivative containing 1,3,4-oxadiazole

The photophysical processes of 9,9-bis[4'-[2'-phenyl-5'-(3'-(methacryl-amido)phenyl)]-1',3',4'-oxadiazolylphenyl]fluorene (F-MAOP) formed by Heck reaction of 9,9-bis(4'-iodophenyl)fluorene (F-IP) and 2-phenyl-5-[3'-(methacrylamido)phenyl]-1,3,4-oxadiazole (OXD) have been carefully studied. The results show that the compound emits blue and blue-violet light and the emission spectra exhibit obvious solvent effect. With the increase of polarity of solvents, the fluorescence spectra change obviously and appear blue shift at room temperature. In addition, the light-emitting can be quenched by both electron donor (N,N-dimethylaniline, DMA) and electron acceptor (C60). When N,N-dimethylaniline is gradually added into the solution of F-MAOP, the emission intensities of fluorescence are unusually increased. But when the concentration of DMA beyond a certain scope, the emission intensities of fluorescence are gradually decreased. The dimolecular exciplex between F-MAOP and C60 are formed and the quenching effect follows the Stern-Volmer equation. Moreover, interaction between F-MAOP and carbon nanotubes (CNTs) is also studied by fluorescent quenching.     

Photophysical processes of a fluorene derivative containing carbazole unit

The photoluminescence properties of 9,9-bis[4'-(9'-carbazovinylene)phenyl]fluorene (F-CZV) formed by Heck reaction of 9,9-bis(4'-iodophenyl)fluorene (F-IP) and N-vinylcarbazole have been carefully studied. The results show that the compound emits blue light and the dimolecular excimer is formed with gradual increase in concentration of F-CZV. The results also indicate the interaction between F-CZV and electron donors (N,N-dimethylaniline) or electron acceptors (dimethylterephthalate, fullerene carbon nanotubes) can be efficiently generated where the processes follow the Stern-Volmer equation. Moreover, when dimethylterephthalate (DMTP) or carbon nanotubes (CNTs) is gradually added into the solution of F-CZV, the emission intensities of fluorescence are unusually increased. But when concentration of dimethylterephthalate or carbon nanotubes beyond a certain scope, the emission intensities of fluorescence are gradually decreased.     

Photophysical properties of safranine O in protic solvents

Spectroscopic and photophysical properties of safranine O (Sf) were investigated in binary water/solvent mixtures. It was found that these properties are strongly solvent-dependent. A blue shift is observed for both the ground-state absorption and the triplet-triplet main absorption band when the solvent polarity augments. At the same time a red shift of the fluorescence emission band takes place. These facts are interpreted in terms of higher dipole moment of the dye molecule in the S(1) state as compared with the S(0) state, while a decrease in the dipole moment of the triplet state T(n) with respect to the triplet state T(1) occurs. The Stokes' shift and the fluorescence lifetime shows a linear correlation with the E(T)(30) parameter, while a non-linear behavior is observed when a correlation with models of a continuous dielectric solvent is attempted. These results suggest the operation of strong specific interactions of Sf with solvent molecules, most likely hydrogen bonding. From fluorescence lifetime and quantum yield determinations, as well as intersystem-crossing quantum yields, the solvent dependence of the photophysical kinetic parameters were obtained. The radiative fluorescence rate constant can be adequately reproduced by calculations based on the UV-Vis absorption and emission spectra, as given by the Strickler-Berg equation.     

Multi-wavelength spectrophotometric determination of the protolytic constants of tetracycline hydrochloride in some nonaqueous-water mixed solvents: a solvatochromism study

Annihilation of the contribution of one chemical component from the original data matrix is a general method in rank annihilation factor analysis (RAFA). However, RAFA is not applicable for studying the protonation equilibria of multiprotic acids but in this study two-rank annihilation factor analysis (TRAFA) was used as an efficient chemometrics algorithm for determination of the protolytic constants (pKa) of tetracycline hydrochloride (TCHC) in some nonaqueous-water mixed solvents such as acetonitrile (AN)-water and methanol (MeOH)-water from the spectral pH-absorbance data. The spectral data was obtained from spectrophotometric acid-base titrations of different solutions of TCHC at (25.0±0.10)°C and an ionic strength of 0.10 M. In TRAFA algorithm the pKa values were obtained with relationship between residual standard deviation (R.S.D.) and hypothetical pKa values. In the case of TCHC, the spectra were divided in two consecutive subdivisions according to their pH range having two pKa and TRAFA was run twice. The validity of the obtained pKa values was checked with well-known chemometrics algorithms such as DATAN, EQUSPEC, SPECFIT/32 and SQUAD. The effects of changing solvent composition on the protolytic constants were explained by linear solvation energy relationships (LSER) utilizing solvatochromic parameters.     

Photocyclization reaction of a diarylmaleimide derivative in polar solvents

Photochromism of a symmetric diarylmaleimide derivative, having two thiophene rings (1), and a non-symmetric derivative having a S,S-dioxide thiophene ring and a thiophene ring (2) as the aryl moieties, was studied in various solvents. The photocyclization quantum yield of gradually decreased with increasing the solvent polarity and the reaction was not observed in polar solvents, such as ethanol and acetonitrile; on the other hand, such a strong solvent dependence of the photocyclization reaction was not observed for ; the different behavior is attributed to the weaker electron donating ability of the S,S-dioxide thiophene ring.     

UV-VIS spectroscopic study of the solvatochromism and chelating reaction of a benzothiazoline merocyanine in mixed solvents

Solvatochromism and chelating reaction of a benzothiazoline merocyanine are studied by UV-VIS spectra in DMF-H₂O, DMF-1,4-dioxane and DMSO-1,4-dioxane. The effect of solvent polarity on UV-VIS absorption maxima and on equlibrium constant K of the chelating reaction is discussed. A linear correlation is obtained between lnK and E_T.     

Studies on the structure behavior of triphenyldichlorophosphorane in different solvents

Triphenyldichlorophosporane, which was prepared according to Appel reaction, was an efficient reagent for alkyl halide synthesis by virtue of having two replaceable groups on "pentavalent" phosphorus. The reaction of triphenylphosphine with hexachloroethane was investigated in different solvents and 31P NMR traced the processes of these reactions. As results, it was found that there was similar high coordinated phosphorus species formed in aromatic solvents and in ring ether type solvents, which had large 1J(P-C) (about 140 Hz) according to 13C NMR experiments. It is indicated that, for some solvent such as benzene or dioxane, solvent molecules might be locked in the high coordinated phosphorus compounds, which in turn would affect the triphenyl groups situated at the equatorial position.     

Reversal in solvatochromism in some novel styrylpyridinium dyes having a hydrophobic cleft

The influence of solvent polarity on the electronic transition of four different N-hexadecyl styrylpyridinium dyes has been investigated in 15 solvents. The E(T)(30) scale has been used to propose a quantitative approach towards the relative stability of the electronic ground and excited state species. The extents of contribution of dipolar aprotic solvents towards the solvation of the excited species have been determined to be 42-48% for some of the dyes. Instead of a steady solvatochromism, all the dyes suffer a reversal in solvatochromism. The transitions of the solvatochromism, referred to as solvatochromic switches, are found to be at E(T)(30) values of approximately 50 for methyl and N,N-dimethylamino substituted dyes while at 37.6 for hydroxyl substituted dye and approximately 45 for 4-(1-methyl-2-phenylethenyl) pyridinium dye. A reversal in the trend of solvent effect in the later dye corresponding to 4-(4-methyl styryl)pyridinium dye has been attributed to an analogy of series and parallel electron flow.     

含萘酰亚胺基元的水杨醛席夫碱的合成及其溶致变色效应

将N-2-（-2-羟乙氧基）乙基4肼基-1,8-萘酰亚胺与水杨醛缩合得到-种新型席夫碱化合物N-（2-（2-羟乙氧基）乙基）4-（2-羟基苯甲醛腙肼基）-1,8-萘酰亚胺（Ⅰ）,对化合物Ⅰ在不同溶剂中的光谱性质研究发现,其表现出特殊的紫外吸收和荧光双重溶致变色效应,可作为荧光分子探针获得应用．对化合物Ⅰ在不同pH值的乙醇水溶液中的光谱性质进行研究,发现该化合物不仅表现出酸碱变色行为,而且具有质子调控荧光分子开关功能及化学荧光传感器特性,有望在酸碱指示剂、分子开关和化学荧光传感器等方面获得应用．     

Polymorphism in a benzo[b][1,4]diazepine derivative: Crystal structure,phase behavior and selective influence of solvents

Ethyl 4-[(Z)-3-ethoxy-2,3-dioxopropylidene]-4,5-dihydro-1H-benzo[b][1,4]diazepine-2-carboxylate forms two polymorphic modifications α and β, which differ in molecular conformations, as well as in the dimension of H-bonded supramolecular motifs in crystals that are a 1D chain or a 0D dimer, respectively. The formation of polymorphs can be controlled by choice of the solvent used. Crystallization from a solution in a polar protic solvent, ethanol, results in the thermodynamically favorable α-form, while using a low-polarity solvent, chloroform, and melt crystallization lead to the metastable β-form.     

Hydrogenation of 4-tert-butylphenol over supported catalysts in different solvents

It has been established that in hydrogenation of 4-tert-butylphenol over Rh/-Al₂O₃ in isopropanol the addition of CH₃COOH increases the yield of 4-tert-butylcyclohexanol.

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, CH₃COOH -4- 4- Rh/-Al₂O₃ .

     

Leaching behavior of metal-containing species in residual oils with different organic solvents

The leaching behavior of two different residual oils is investigated with 24 organic solvents including alkanes, aromatics, esters, ethers ketones, alcohols and nitrogen compounds. A 2-g portion of sample oil is shaken with 20 ml of the organic solvent. The leaching of the organic matrix of the oil is determined by weighing the dissolved organic matrix after removal of solvent. The leaching of vanadium, iron and nickel was determined by flame atomic absorption spectrophotometry after ashing of the dissolved fraction. The leaching of those metals depends strongly on the solvent used; for example, vanadine is almost completely leached into toluene, but only slightly into methanol. The leaching of iron is poor compared with that of vanadium or nickel. In most solvents, leaching of those metal-containing species is poorer than that of organic material. Exceptionally, N,N-dimethylformamide is more efficient in leaching vanadium species than organic material.     

Thermo-cage opening of 4-iodo-1-vinylcubane to a novel styrene derivative

Cubane (1) and its derivatives have been cited for exhibiting unusual properties, including explosive and antiviral activity. An additional characteristic of these compounds is their tendency to undergo cage opening under certain conditions. In our attempt to polymerize 4-iodo-1-vinylcubane (4), 4-vinyl-trans-β-iodostyrene (10) was formed quantitatively. By examining both the thermolytic and Lewis acid-assisted rates, a possible mechanism for the rearrangement of 4→10 has been proposed.