Hierarchical self-organization of perylene bisimide--melamine assemblies to fluorescent mesoscopic superstructures

A series of three perylene tetracarboxylic acid bisimide dyes 3a-c bearing phenoxy substituents at the four bay positions of the perylene core were synthesized and their complexation behavior to complementary ditopic dialkyl melamines 8a-c was investigated. Binding constants and Gibbs binding energies for the hydrogen bonds between the imide and the complementary melamine moiety have been determined in several solvents by NMR and UV/Vis titration experiments with monotopic model compounds 5 and 9. The effects of the solvent polarity and specific solvent-solute interactions on the degree of polymerization of (3 x 8)n are discussed, and a general formula to estimate the chain length of [AA-BB]n nylon-type supramolecular polymers is derived. In addition to the formation of a hydrogen-bonded supramolecular chain. pi-pi interactions were observed for perylene bisimide-melamine assemblies 3b x 8b and 3b x 8c in aliphatic solvents. The orthogonal nature of hydrogen bonding and pi-pi interactions leads to three-dimensional growth yielding large-sized aggregates already in dilute solution. On suitable substrates, densely intertwined networks of nano- to mesoscopic strands are formed which have been investigated by electron microscopy, confocal fluorescence microscopy and optical polarization microscopy. The high fluorescence and excellent photostability of these superstructures is promising for future studies on energy migration and artificial light harvesting at the nano- and mesoscopic length scale.     

A method for calculating the Gibbs energy of nonspecific solvation

A method for calculating the Gibbs energy of nonspecific solvation of nonelectrolytes was suggested. The new equation for the Gibbs energy of nonspecific solvation contains one solvent parameter that characterize nonspecific solvent-solute interactions and two experimental Gibbs energies of solvation in two standard solvents. The method is applicable to a wide range of solutes and solvents. It was successfully used to describe some 800 Gibbs energies of solvation for systems without specific solvent-solute interactions.     

Weak complexes of sulphur and selenium: a thermodynamic view on solvent effects in mixed solvents

The effect of mixed solvent on complex stability is discussed from a thermodynamic standpoint. The variation in the free energy of formation for a complex species in different solvent mixtures is an indication of solvent-solute and solvent-solvent interactions. The complexity of the systems in mixed solvents makes entropy data difficult to interpret. Evidence is given on solvent-solvent interactions.     

苯并吲哚半菁、二次甲基菁染料的微波合成、光谱性能及其与生物分子的相互作用

采用微波技术,分别以N-烷基-2,3,3-三甲基-4,5-苯并吲哚六氟合磷酸盐与二甲氨基苯甲醛或3-吲哚甲醛为原料,在哌啶的催化下快速合成了4种苯并吲哚半菁染料H1～H4和4种苯并吲哚二次甲基菁染料F1～F4,并采用UV-Vis,1H NMR,IR,元素分析确证了产物的结构.研究了染料在不同溶剂中的吸收光谱性质,结果显示:两类染料在质子性溶剂中随着溶剂极性的增加最大吸收波长出现蓝移;而在非质子性溶剂中随着溶剂极性的减小最大吸收波长发生红移.同时,研究了染料H3和F2在生理条件下与鲑鱼精DNA、牛血清白蛋白、溶菌酶、淀粉酶和糜蛋白酶的相互作用,发现染料H3的荧光强度随着DNA浓度的增加而增强.     

Studies on the electronic absorption spectra of some monoazo derivatives

The electronic absorption spectra of a series of azo dye compounds containing -Cl, -SO3H and -OH groups were recorded in twenty one solvents with different polarities. The solvents were selected to cover a wide range of parameters (refractive index, dielectric constant and hydrogen bonding ability). Solvent-induced effect on the maximum absorption band frequencies of azo dye compounds are described in terms of solute-solvent interactions. Multiple linear regression equation for νmax was performed using polarizability-polarity parameters and Kamlet-Taft solvatochromic parameters. The results help to assign the solvent-solute interactions and the solvatochromic potential of the investigated compounds. It is concluded that the electronic of the substituent and hydrogen bonding acceptor ability of the solvents are the major factors to the interaction in solutions.     

Inter- and intramolecular hydrogen bonding in phenol derivatives: a model system for poly-L-tyrosine

The ultrafast dynamics of solutions of phenol and two phenol derivatives--hydroquinone (1,4-benzenediol) and pyrocatechol (1,2-benzenediol)--have been studied with Optically Heterodyne-Detected Optical Kerr-Effect (OHD-OKE) spectroscopy. The solvents, methanol and acetonitrile, were selected to provide strong and weak solvent-solute hydrogen-bonding interactions, respectively, while pyrocatechol features an intramolecular hydrogen bond. Together these provide a series of model systems for polypeptides such as polytyrosine, which facilitate the direct study of inter- and intramolecular hydrogen bonding. A broad contribution to the Raman spectral density of the methanol solutions at frequencies between 150 and 300 cm(-1) has been observed that is absent in acetonitrile. This contribution has been assigned to solvent-solute hydrogen-bond stretching vibrations. The OHD-OKE response of poly-L-tyrosine has been measured and was found to contain a similar contribution. Density functional theory geometry optimizations and normal mode calculations have been performed using the B3LYP hybrid functional and 6-311++G** basis set. These have yielded a complete assignment of the low-frequency Raman and far-infrared spectra of pyrocatechol for the first time, which has provided information on the nature of the intramolecular hydrogen bond of pyrocatechol.     

Solvent effects on infrared spectra of methyl 4-hydroxybenzoate in pure organic solvents and in ethanol/CCl4 binary solvents

Infrared spectroscopy studies of methyl 4-hydroxybenzoate (MHB) in 17 different organic solvents and in ethanol/CCl4 binary solvent were undertaken to investigate the solvent-solute interactions. The frequencies of carbonyl stretching vibration nu(C=O) of MHB in single solvents were correlated with the solvent acceptor number (AN) and the linear solvation energy relationships (LSER). The assignments of the two bands of nu(C=O) of MHB in alcohols and the single one of that in non-alcoholic solvents were discussed. The shifts of nu(C=O) of MHB in ethanol/CCl4 binary solvents showed that several kinds of solute-solvent hydrogen bonding interactions coexisted in the mixture solvents, with a change in the mole fraction of ethanol in the binary solvents.     

Dissolution parameters reveal role of structure and solvent in molecular gelation

The relationship between thermodynamic dissolution parameters (enthalpy and entropy) and gelation ability was examined for two different classes of compounds in three different solvent systems. In total, 11 dipeptides and 19 pyridines were synthesized and screened for gelation in aqueous and organic solvents, respectively. The dissolution parameters were determined from the variable-temperature solubilities using the van't Hoff equation. These studies revealed that the majority of gelators had higher dissolution enthalpies and entropies compared to nongelators, consistent with the notion that gelators have stronger intermolecular interactions and more order in the solid state. The dissolution parameters were also found to be solvent-dependent, suggesting that solvent-solute interactions are also important in gelation. Overall, these results indicate that converting nongelators into gelators is attainable when structural modifications or a change in solvent lead to increases in the dissolution parameters.     

Solvent effects on infrared spectra of 2-acetylthiophene in organic solvents

Infrared spectroscopy studies of 2-acetylthiophene (ACTH) in 18 different organic solvents, both polar and non-polar, were undertaken to investigate the solvent-solute interactions. The frequencies of carbonyl stretching vibration upsilon(C=O) of ACTH were correlated with the properties such as the solvent acceptor number (AN) and the linear solvation energy relationships (LSER). The solvent-induced stretching vibration frequency shifts showed a better correlation with the LSER than the AN. A six-membered ring-like hydrogen bonding structure was presented and the solvent effects of ACTH in alcohol solvents were investigated in detail.     

Spectroscopic properties of fluoroquinolone antibiotics in water-methanol and water-acetonitrile mixed solvents

The fluorescence properties of ofloxacin (OFL), norfloxacin (NOR) and flumequine (FLU) were studied in H2O-CH3OH and H2O-CH3CN mixed solvents because these solvents were thought to behave as a biological mimetic system. The emission spectra of OFL and NOR were very sensitive to the composition of the solvents. In the Lippert-Mataga analysis of the steady-state fluorescence data of OFL and NOR, clear reverse solvatochromism was exhibited in both mixed solvents. This observation can be explained by the twisted excited-state intramolecular charge transfer, which is accelerated by water. Theoretical treatments further support these results. The radiative and nonradiative rate constants were analyzed as a function of solvent dipolarity-polarizability (pi*) and hydrogen-bond donor acidity (alpha). These results were well consistent with the suggested mechanism of the excited-state chemical process of OFL and NOR, which depended upon the solvent-solute interactions such as bulk dielectric effects and specific hydrogen-bonding interactions. However, the influence of dielectric effects was more significant. The solvent structures of H2O-CH3CN and the preferential solvation by water were also examined. The emission spectra of FLU do not exhibit any characteristic responses to the properties of the environment.     

Influence of the solvent on the surface-enhanced raman spectra of ruthenium(II) bipyridyl complexes

In the present work a new dye, [Ru(dcbpyH2)2(bpy-TPA2)](PF6)2, and the well-known (Bu4N)2[Ru(dcbpyH)2(NCS)2] complex were investigated. The electronic transitions of both dyes showed solvatochromic shifts due to specific interactions of the ligands with the solvent molecules. The surface-enhanced Raman (SER) spectra of the dyes dissolved in water, ethanol, and acetonitrile were measured in silver and gold colloidal solutions. The results demonstrate that the dyes were adsorbed on the metallic nanoparticles in different ways for different solvents. It was also found that in the gold colloid, the aqueous solutions of both dyes did not produce any SERS signal, whereas in ethanolic solution the SERS effect was very weak. Deprotonation, H-bonding, and donor-acceptor interactions seem to determine these different behaviors. Our results indicate the important role of the charge-transfer mechanism in SERS.     

Bidirectional switching of near IR emitting boradiazaindacene fluorophores

Two novel distyryl-boradiazaindacene dyes with dimethylaminostyryl and pyridylethenyl substituents display opposite spectral shifts on protonation with TFA in organic solvents. This bidirectional switching of the dyes can be shown to be directly related to ICT donor and acceptor characteristics of the substituents attached to the BODIPY core. The observed spectral response of these dyes could be very useful in the design of novel NIR fluorescent ratiometric probes for pH.     

Hydrogen bonding properties of Coumarin 151, 500, and 35: the effect of substitution at the 7-amino position

The steady-state spectral properties (absorption and emission) of three structurally similar Coumarin dyes, C151, C500, and C35 were investigated in 13 different solvents. A Kamlet-Taft (KT) analysis of the spectral peak frequencies reveals that, in addition to polarity, hydrogen bonding between the carbonyl oxygen and a protic solvent in the excited state imparts maximum stabilization for C151 and minimum for C35, while that for C500 lies in between. The spectral properties of the three dyes in two solvents, chloroform and THF, which have similar polarity in the KT scale but have only hydrogen-bond donor (chloroform) and hydrogen-bond acceptor (THF) properties, are seen to be sensitive to the substitution pattern at the 7-amino position. In addition, a slow emission spectral relaxation is observed for C151 and C500 having a time constant of approximately 500 ps in chloroform. For C35 this was too fast to be detected by the time resolution of our setup. The exact reason for this slow spectral relaxation in chloroform is unclear at present, and further studies are needed to understand clearly the structural effects on the hydrogen bonding dynamics of these dyes.     

Influence of the solvent nature on the association processes of different dye molecules

The spectral characteristics of mixture of Rhodamine dyes with Methylene Blue have been studied in different solvents. The influence of the solvent nature on the development of different associations of the molecules of the investigated dyes has been established. It has been shown that the main influence on these processes is exerted by the medium through its microproperties.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 26, No. 6, pp. 669–675, November–December, 1990.     

Spectral properties and orientation of voltage-sensitive dyes in lipid membranes

Voltage-sensitive dyes are frequently used for probing variations in the electric potential across cell membranes. The dyes respond by changing their spectral properties: measured as shifts of wavelength of absorption or emission maxima or as changes of absorption or fluorescence intensity. Although such probes have been studied and used for decades, the mechanism behind their voltage sensitivity is still obscure. We ask whether the voltage response is due to electrochromism as a result of direct field interaction on the chromophore or to solvatochromism, which is the focus of this study, as result of changed environment or molecular alignment in the membrane. The spectral properties of three styryl dyes, di-4-ANEPPS, di-8-ANEPPS, and RH421, were investigated in solvents of varying polarity and in model membranes using spectroscopy. Using quantum mechanical calculations, the spectral dependence of monomer and dimer ANEPPS on solvent properties was modeled. Also, the kinetics of binding to lipid membranes and the binding geometry of the probe molecules were found relevant to address. The spectral properties of all three probes were found to be highly sensitive to the local environment, and the probes are oriented nearly parallel with the membrane normal. Slow binding kinetics and scattering in absorption spectra indicate, especially for di-8-ANEPPS, involvement of aggregation. On the basis of the experimental spectra and time-dependent density functional theory calculations, we find that aggregate formation may contribute to the blue-shifts seen for the dyes in decanol and when bound to membrane models. In conclusion, solvatochromic and other intermolecular interactions effects also need to be included when considering electrochromic response voltage-sensitive dyes.     

新型水溶性不对称五甲川菁染料的合成、光稳定性及蛋白质的荧光标记

合成并表征了系列水溶性五甲川菁染料, 研究了其在不同溶剂中的光谱性能. 结果表明, 染料在水中的最大吸收和荧光光谱在647~665 nm波长范围内, 荧光量子产率达到0.1左右. 考察了N位取代基对染料水溶液光稳定性的影响, 结果表明, 在N原子上引入带有苯环结构和大体积的磺酸基, 可以提高染料的光稳定性. 高效液相色谱(HPLC)分析结果表明, 染料4a的N-羟基琥珀酰亚胺(NHS)活性酯标记牛血清白蛋白(BSA)的检测限为1.2×10^-8 mol/L, 与紫外检测相比, 检测灵敏度提高了近2个数量级.     

Solvatochromic behaviours and structure–spectra relationships of 4-carboxyl-2,6-dinitrophenylazohydroxynaphthalenes

Comprehensive electronic absorption spectra of a new dye series, 4-carboxyl-2,6-dinitrophenylazohydroxynaphthalenes have been investigated in solvents of varying polarities. The solvent dependent UV–vis spectral shifts were analysed using some solvent physical parameters such as refractive index, dielectric function, hydrogen bonding acceptor ability, orientation of polarization and others. The observed spectral shifts were correlated with different solute–solvent interaction mechanisms using simple and multiple linear regression analyses. The results of the curve fitting coefficients enabled us to classify the various interactions of solvents with the dyes and relate the solvatochromic behaviours to the substituent effects on the dye molecules. Charge-transfer complexation occurring between one of the congeners and N,N′-dimethylformamide was extensively studied and discovered to be both concentration- and temperature-dependent.The electronic character and the chemical nature of the solvents as well as the chemical nature of the other substituents, apart from the common hydroxyl group, are important factors for the observed solvatochromic properties of the 4-carboxyl-2, 6-dinitrophenylazohydroxynaphthalenes.     

Solvatochromism and Preferential Solvation of 4-Pentacyanoferrate 4′-Aryl Substituted Bipyridinium Complexes in Binary Mixtures of Hydroxylic and Non-hydroxylic Solvents

The intense solvatochromic behavior of several pentacyanoferrate complexes with aryl substituted 4,4′-bipyridines acting as ligands, was investigated in six hydroxylic and non hydroxylic solvents using UV-Visible spectroscopy. The metal-to-ligand-charge-transfer bands of the visible spectra of these compounds proved to be markedly affected by solvent polarity. In order to quantify the extent of the observed solvatochromism and reveal the dominant interactions which take place in the cybotactic region, resulting in solvatochromism, the Kamlet-Taft equation was used. This is a multiparametric linear-solvation-energy-relationship (LSER) widely used for the study of solvent effects on various physicochemical properties. Through this analysis it was proved that both specific and non specific interactions contribute to the observed solvatochromism. Furthermore, the preferential solvation of the complex salts was studied in binary solvent mixtures. Solvatochromism was used as the key approach to rationalize solvent-solute and solvent-solvent interactions in the binary solvent mixtures studied.     

A time-resolved fluorescence study of the dynamic stokes shift of trans-4-dimethylamino-4'-cyanostilbene

The time-resolved fluorescence Stokes shift of trans-4-dimethylamino-4'-cyanostilbene has been measured as a function of temperature in polar solvents. Fluorescence spectra were found to exhibit exponential rise times of 80 to 640 ps between 297 and 250 K. These observations are attributed to two independent relaxation processes in alcohols: to reorientation of the solvent cage and to relaxation of the solute. The rate of the former process depends on the strength of specific solvent-solute interactions.