The influence of solvent polarity and viscosity on fluorescence of quinolizinium salts

The effects of dielectric constant, viscosity and polarity of the solvents used on the relative fluorescent emission of 2,3-diphenylquinolizinium bromide and 2(p-dimethyl-amino)styryl-3-methylquinolizinium bromide are described. These salts were entirely dissolved in ten different solvents. The 2(p-dimethylamino)styryl derivative produced different ionic species, and was a fluorescent acid-base indicator. The fluorescence of these quinolizinium salts is shown to increase with greater viscosity of the medium.     

Influence of micellar media on the fluorescence of various benzo- and methyl-quinolizinium salts

The bebaviour of several different micelar systems (anionic, cationic and non-ionic) on the fluorescence of quinolizinium salts is studied. Important factors, such as pH and ionic strength that influence fluorescence parameters, are discussed. Fourteen quinolizinium salts (benzo and methyl derivatives) are examined as fluorescent probes in micellar media. All of them showed a marked increase of fluorescence intensity when sodium dodecyl sulfate solutions of critical micelle concentration (CMC) are added. The presence of non-ionic surfactants did not change the fluorescent emission of the probes. The emission intensity is much decreased when N-cetyl-N,N,N- trimethylammonium bromide concentrations are above the CMC. Changes in pH ido not significantly affect the fluorescence intensity of the benzo derivatives. Increasing the ionic strength decreases the fluorescence. For 9-cyanobenzo[a]phenanthro [9,10-g] quinolizinium chloride, the spectrum changes when the surfactant concentration is high than the CMC thereforre this compound is considered to be a good fluorescent probe in icell     

Ultrasensitive fluorescent probe for the hydrophobic range of solvent polarities

The new 3-hydroxychromone derivative 2-(6-diethylaminobenzo[b]furan-2-yl)-3-hydroxychromone (FA) displays a dramatic solvent-dependent transformation of fluorescence spectra in the range of low-polarity solvents. The two well-separated emission bands change their relative intensities so that the short-wavelength band being of a very low intensity in hexane becomes dominant in the more polar ethyl acetate and trichloromethane. We suggest the participation in this effect of excited-state intramolecular proton transfer, which is characteristic for other 3-hydroxychromone and 3-hydroxyflavone derivatives, in the range of solvents of much higher polarities. Because of these unique properties, a number of spectroscopic parameters (positions of absorption and two fluorescence maxima, the ratio of their intensities and the fluorescence quantum yield) can be measured in this solvent range with multiparametric analysis of the data. In terms of solvent polarity, the shifts in both emission bands and their intensity ratio demonstrate a good correlation with empirical polarity scales E_T^N, P_y and SPP, while the absorption spectra reveal some deviations for the tested oxygen-containing solvent molecules. A good cross-correlation is observed between fluorescence spectral shifts and the ratio of band intensities. The latter provides the means for a dramatic amplification of solvent response. Thus, a new approach for ultrasensitive scaling and probing the solvent polarity in the low-polararity range can be suggested. It involves very simple ratiometric measurements at two emission bands and can be posed for a variety of applications. We present examples of these applications for distinguishing of polarities between methylated benzene derivatives, for quantitative assay of polar impurities in low-polar solvents and for detection of the changes of solvent polarity as a function of temperature.     

High boron content carboranyl-functionalized aryl ether derivatives displaying photoluminescent properties

The reaction of alpha,alpha'-bis(3,5-bis(bromomethyl)phenoxy-p-xylene (3) with 4 equiv of the monolithium salt of 1-Ph-1,2-C2B10H11 or 1-Me-1,2-C2B10H11 gave the corresponding neutral carboranyl-functionalized aryl ether derivatives closo-4 and closo-5, respectively. These compounds contain four closo clusters that were degraded using basic conditions with KOH in EtOH, affording the corresponding nido-6 and nido-7 as potassium salts. Nido species were also isolated with tetramethylammonium as cation giving compounds nido-8 and nido-9 in good yield. The potassium salts showed good solubility in water and polar solvents. All these compounds were characterized by 1H, 11B and 13C NMR spectroscopy and UV-vis. The electronic data in different solvents indicated a solvatochromic shift for all compounds and a red shift of the absorption maxima for the nido species with respect to the closo derivatives. These neutral and anionic carboranyl-functionalized aryl ether derivatives represent a new family of high boron content luminescent compounds that show strong fluorescence emission in different solvents at room temperature. This phenomenon is very interesting considering the fact that none of the precursors have such a property. The fluorescence emission depends on the cluster substituent (Ph or Me) and the solvent polarity. Additionally, the fluorescence emission intensity was clearly dependent on the solvent polarity; the closo species showed strongest fluorescence intensities in the non-polar solvents, while anionic species were highly emissive in polar solvents.     

Bichromophoric hemicyanine dyes as fluorescence probes applied for monitoring of the photochemically initiated polymerization

The spectroscopic properties of series homodimmeric hemicyanine dyes based on (p-N,N-dimethylaminostyryl)benzothiazolium, (p-N,N-dimethylaminostyryl)benzoxazolium, (p-N,N-dimethylaminostyryl)-2,3,3-trimethyl-3H-indolium residues were determined. The absorption and fluorescence spectra of the dyes under study were measured in different polarity solvents at room temperature. On the basis of the solvatochromic behavior the ground state (μ_g) and excited state (μ_e) dipole moments of bis-(N,N-dimethylaminostyryl) derivatives were evaluated. The dipole moments (μ_g and μ_e) were estimated from solvatochromic shifts of absorption and fluorescence spectra as function of dielectric constant (ε) and refractive index (n) of applied solvents. The absorption and fluorescence spectra are only slightly affected by the solvent polarity. The analysis of solvatochromic behavior of the fluorescence spectra as a function of Δf (ε, n) revealed that the emission occurs from a high polarity excited state. The large dipole moment changes along with the red-shifted fluorescence, as the solvent polarity is increased, demonstrates the formation of an intramolecular charge transfer state (ICT). Six bichromophoric hemicyanine dyes, possessing benzothiazole, benzoxazole or indolinium group linked by 5 or 10 methylene groups were evaluated as fluorescence probes applied for monitoring of the polymerization process. The study on the changes in fluorescence intensity and spectroscopic shift of studied compounds were carried out during photochemically initiated polymerization of 2-ethyl-2-(hydroxymethyl)-propane-1,3-diol triacrylate (TMPTA).     

Synthesis and spectral properties of long-wavelength fluorescent dyes

Benzo[a]phenoxazinium salts were synthesised by reacting 5-alkylamino-2-nitrosophenol hydrochloride with N-alkylated-naphthylamine in good to excellent yields. Photophysical properties of these fluorophores with emphasis in solvent effects were studied. Remarkable shifts in the absorption and emission maximum have been observed as a function of polarity and proton accepting capability of the solvents. The influence on the fluorescence quantum yield was also studied.     

苯乙烯基吡嗪类化合物的构象研究

有选择地合成了四种结构不同的苯乙烯吡嗪衍生物，测定了它们在不同极性溶剂中的吸收光谱和荧光光谱，根据其在基态条件下可能的分子构象和所得到得到的光谱数据，进一步对该类分子的最佳发光构象做出较为肯定的结论。     

两个新的苯并噻唑衍生物的合成与光物理性质

以苯并噻唑、苯乙酰基和吡啶阳离子为电子受体,二乙烯基苯为共轭桥,合成了两个新的A-π-A′型苯并噻唑衍生物:4-(2-苯并噻唑)-乙烯基查尔酮(1)和4-{4-[2-(苯并噻唑)乙烯基]苯乙烯基}-N-甲基吡啶碘盐(2).研究了它们在溶液和固体基质中的光物理性质.研究发现:染料2由于具有较强的极性和较好的平面性,从而具有较长的吸收、发射峰和较强的荧光发射.有机染料在聚甲基丙烯酸甲酯/溶胶-凝胶复合玻璃中的发光行为与聚甲基丙烯酸甲酯和溶胶-凝胶玻璃二者的基质性质有关,同时由于固体基质中分子发生聚集的可能性降低,荧光强度相对于同浓度溶液增强,稳定性提高.     

Photophysics of benzazole derived push–pull butadienes: A highly sensitive fluorescence probes

Two new homologues of 1,4-diphenylbutadiene, namely, 1-(2-benzazolyl)-4-(p-dimethylaminophenyl)buta-1,3-diene have been synthesized and their absorption and fluorescence properties have been investigated in different organic solvents. The absorption spectra are less sensitive to the solvent polarity than the corresponding fluorescence spectra, which show dual emission and high solvatochromic effect in polar solvents. Using an efficient solvatochromic method, a large excited state dipole moment parallel to the smaller ground state dipole moment was calculated. Other properties of the lowest excited state such as the planar ICT B_u nature, fluorescence quantum yield and the basicity of the two nitrogen atoms (of the benzoxazole or benzothiazole ring as well as the amino group) were studied by spectroscopic techniques and semiempirical AM1 quantum chemical calculations. The findings have been presented and discussed along with the promising fluorescence probing and pH-sensing properties of these two dienes. The main spectroscopic properties of the two derivatives have been also compared.     

Microwave-assisted solvent-free catalyzed synthesis and luminescence properties of 1,2,4,5-tetrasubstituted imidazoles bearing a 4-aminophenyl substituent

A solvent-free microwave-assisted four-component synthesis of 1,2,4,5-tetrasubstituted imidazoles bearing a 4-aminophenyl substituent was studied by condensation of p-phenylenediamine, aryl diketone, benzaldehyde derivatives and ammonium acetate in the presence of solid support silica gel and catalyst Keggin-H₃[PW₁₂O₄₀]. The effects of four components molar ratio along with catalyst loading, irradiation time on the yields were investigated. Also, the structures of synthesized compounds were characterized by FT-IR, HRMS, ¹H NMR and ¹³C NMR spectroscopy. Furthermore, their ultraviolet–visible maximum absorption, liquid fluorescence emission maximum and quantum yields were, respectively, measured in 0.05 M H₂SO₄ aqueous solution and in dichloromethane. Simultaneously, solid fluorescence spectra were determined in the powder state. The relationships between the optical behavior and the polarity of the solvents for some compounds were assessed. The results showed that the fluorescence quantum efficiency was increased by introducing amino phenyl in comparison with benzyl on 1-position of trisubstitued imidazoles. The compounds synthesized were sensitive to the polarity of the solvents.     

Effect of reaction medium on the ionizing radiation-initiated cationic copolymerization of styrene derivatives

The influence of reaction medium polarity on the ionizing radiation-initiated copolymer-ization of styrene derivatives involving unpaired carbocations is examined. In the copo-lymerization of nonpolar monomers such as p-CH3styrene/styrene, a small effect consistent with that predicted by Laidler-Eyring theory is found. In the copolymerization of nonpolar/polar monomer pairs such as p-CH3styrene/p-Clstyrene and styrene/p-Clstyrene, any such effect is masked by specific solvation phenomena. A competition between such phenomena appears to exist, in which the different cations are dominated by different interactions. The p-Clstyryl cation appears to undergo strong intramolecular complexation with the penultimate aromatic ring in nonpolar conditions; thus, this cation displays increased se-lectivity toward monomers best able to disrupt the complex. The p-CH₃styryl and styryl cations do not appear to be subject to such strong complexation; thus, in nonpolar solvent, their selectivity tends towards monomers with the highest cation-solvating ability. The differing copolymerization behavior of the p-Clstyryl cation is consistent with the findings of previous investigations of the effect of reaction medium on chain transfer with these monomers. © 1995 John Wiley & Sons, Inc.     

The rearrangement and solvolysis of furfuryl arenesulfinates

Furfuryl benzenesulfinate, furfuryl p-toluenesulfinate and 5-nitrofurfuryl benzenesulfinate were synthesized, and their behaviour under various conditions was investigated. The first two esters were found to undergo readily rearrangement to sulfone. In nonhydroxylic solvents, a mixture of furfuryl aryl sulfone and 2-methyl-3-furyl aryl sulfone is obtained. The ratio between the two sulfones changes with the polarity of the solvent. In hydroxylic solvents, only rearrangement to the furfuryl aryl sulfone takes place, and this is accompanied by solvolysis of the ester. A kinetic study of the reaction in ethanol and aqueous ethanol solvents indicated an ionization mechanism. It is suggested that under these conditions the sulfone is formed by recombination of ion pairs. A kinetic study of the rearrangement under nonsolvolytic conditions was also performed in order to obtain the effect of the solvent and the effect of added salts on the rate of rearrangement. This study has shown that the rate of rearrangement is sensitive to the ionizing power of the solvent. The addition of perchlorate was found to have a stronger effect on the formation of the furfuryl sulfone than on the 2-methyl-3-furyl sulfone. In this case an ionic mechanism is also suggested, and the two sulfones may arise by recombination from two different species of ion pairs.     

Synthesis and fluorescence properties of 2-aryl-3-hydroxyquinolones, a new class of dyes displaying dual fluorescence

A series of 2-aryl-3-hydroxyquinolones (3HQs) with different electron donating aryl substituents at the position 2 were synthesized. Their absorption and fluorescence properties were studied in solvents of medium and high polarity. Almost all the synthesized 3HQs display dual fluorescence in the tested solvents, in line with an excited state intramolecular proton transfer reaction. For N-methyl substituted compounds, the intensity ratio of the two emission bands was found to be exquisitely sensitive to solvent polarity, with a two orders of magnitude change from toluene to dimethylsulfoxide. Consequently, these compounds appear as prospective polarity fluorescent labels for proteins and nucleic acids.     

Polymerization of acrylamide in various solvents in the presence of Lewis acids

The radical polymerization of acrylamide in various solvents in the presence of Lewis acids has been investigated. Considerable effects of LiBr, LiCl and CaCl₂ on the total reaction rate and the values of k_p and k₁ for polymerization in DMSO or THF have been shown. For the polymerization of acrylamide in aqueous solution, addition of the salts does not affect the kinetic behaviour of the process. The observed effect of salts arises from complexation between the salt and the monomer and/or the propagating radicals.     

Spectral behaviour of eosin Y in different solvents and aqueous surfactant media

Photophysical behaviour of the anionic xanthene dye, eosin Y (EY) was investigated in solvents of different polarities as well as in the presence of aqueous cationic surfactants. From the correlation between E(T)(30) and Kosower Z values of EY in different solvents, subsequent parameters for EY were determined in the presence of surfactants. A red shift, both in the absorption and emission spectra of EY, was observed with decreasing solvent polarity. Dimerisation of EY was found to be dependent on solvent polarity. Cationic surfactants retarded the process of dimerisation, which were evident from the lower dimerisation constant (K(D)) values, compared to that of in pure water. Dye-surfactant interaction constants were determined at different temperatures (298-318 K) and subsequently the thermodynamic parameters, viz., ΔG°, ΔH° and ΔS° were evaluated using the interaction constant values. The fluorescence spectra of EY followed the same trend as in the absorption spectra, although with lesser extents. Stokes shifts were calculated and correlated with the polarity of the medium. Fluorescence of EY was initially quenched by the cationic surfactants in their pre-micellar region, which then followed a red shift with intensity enhancement. Fluorescence quenching was found to be of Stern-Volmer type where the excited state lifetime of EY remained unchanged in different surfactant media. However, the anisotropy value of EY was changed in the post micellar region of surfactants.     

Flow injection determination of cationic surfactants by using N-bromosuccinimide and N-chlorosuccinimide as new oxidizing agents for luminol chemiluminescence

Two highly sensitive chemiluminescence (CL) systems are described. The method is based on the CL generated during the oxidation of luminol by N-bromosuccinimide (NBS) and N-chlorosuccinimide (NCS) in alkaline medium. The emission intensity is reduced by the presence of some surfactants at concentrations lower than critical micelle concentration (cmc).A new, simple, rapid and selective flow injection CL method for the determination of cationic surfactants such as dodecyltrimethylammonium bromide (DTAB), cetyltrimethylammonium bromide (CTAB) and cetylpyridinium chloride (CPC) is proposed. Their determinations are based on the reducing effect on the emission intensity of NBS-luminol and NCS-luminol chemiluminescent reactions. The effect of analytical and flow injection analysis (FIA) variables on these CL systems and on the determination of the cationic surfactants are discussed. The optimum parameters for the determination of cationic surfactants were studied and were found to be the following: luminol, 1×10⁻⁶ M; NBS and NCS both, 5×10⁻² M; NaOH, 5×10⁻² M and flow rate, 3.5 ml min⁻¹.     

Synthesis of novel aryl-1,2-oxazoles from ortho-hydroxyaryloximes

The reaction of ortho-hydroxyaryloximes with p-toluenesulfonyl chloride in the presence of an amine base efficiently generates the corresponding aryl-1,2-oxazole. Investigations revealed that solvent polarity greatly affected the rate of the reaction with faster rates observed in more polar solvents. The reaction proceeds to completion in only a few minutes in acetonitrile at room temperature, and the synthesis of four novel aryl-1,2-oxazoles is presented.     

Effect of solvent polarizability on dual fluorescence of EE-1-phenyl,4-(1′-pyrenyl)-1,3-butadiene

The properties of the lowest excited states of EE-1-phenyl,4-(1′-pyrenyl)-1,3-butadiene were studied by absorption and emission spectrometry in solvents of different polarity and polarizability. The effect of the latter on the energy and relative position of the two lowest excited singlet states (of B_u and A_g parentage) was investigated. Dual fluorescence was observed in low polarizability solvents at room temperature. The emission from a thermally populated upper state disappears at low temperature and in higher polarizability solvents, such as CS₂, where the lowest excited state acquires an allowed character. The excited molecule relaxes mainly by the radiative pathway. Internal conversion also plays an important role while the triplet population is scarce and photoisomerization is practically negligible. The behaviour is compared with those of related compounds.     

Design and Synthesis of Novel Organic Luminescent Materials Based on Pyrazole Derivative

Five new materials based on pyrazole derivatives have been synthesized and characterized as organic light‐emitting devices. This report presents a novel approach to combine pyrazole with aromatic hydrocarbons via methylene. The formed molecules exhibited twisted structures, which resulted in high glass transition temperatures (T_g), which ranged from 83.0 to 101.1°C. They also had high optical band gaps (E_g); most of their optical band gaps are determined by the absorption edge technique as 3.43 to 3.66 eV, evaluated photophysical properties of these synthesized novel chromophores, the optical properties such as maximum absorption and emission wavelengths (λ; nm), molar extinction coefficients (ε; cm^?1·M^?1), Stokes' shifts (Δλ_ST; nm), and quantum yields (φ_F). These compounds exhibited intense absorption bonds between 230 and 350 nm, and the effect of solvent polarity on emission of these pyrazole derivatives was also studied. In addition, they showed blue fluorescence in different solvents and bathochromic shift with the increase in the solvent polarity.