Near-infrared fluorescent probes: synthesis and spectroscopic investigations of a few amphiphilic squaraine dyes

With the objective of developing near-infrared fluorescence probes for biological applications, a few squaraine dyes 3a-d, containing amphiphilic substituents, were synthesized and their photophysical properties have been investigated in the presence and absence of the organized media. These dyes exhibited absorption in the range 630-650 nm, with significant absorption coefficients (epsilon = 1-3 x 10(5) M(-1) cm(-1)) in the aqueous medium. The fluorescence spectra of these dyes showed emission maximum from 660 to 675 nm, depending on the nature of substituents. The fluorescence quantum yields were in the range from 0.15 to 0.21 in ethanol, but 10 times lower values were observed (phi(f) = 0.01-0.02) in the aqueous medium. In the presence of micelles such as cetyltrimethylammonium bromide, sodium dodecyl sulfate, and Triton X-100, these dyes showed negligible changes in their absorption properties, whereas a significant enhancement (5-10-folds) in their fluorescence yields was observed. Picosecond time-resolved studies indicated that these dyes show single-exponential decay in ethanol and ethanol-water mixtures; however, they exhibit biexponential decay with longer lifetimes in the presence of the micellar media. The results indicate that these novel amphiphilic squaraine dyes 3a-d, which exhibit favorable photophysical properties, good solubility in the aqueous medium, and interact efficiently with micelles, can have potential biological applications as near-infrared fluorescence sensors.     

THE FLUORESCENCE PROPERTIES OF ORTHO AMINOBENZOATE ANESTHETICS IN DEFINED SOLVENTS AND PHOSPHOLIPID VESICLES

Abstract— The fluorescence properties of three ortho aminobenzoate local anesthetics have been determined in a variety of solvents. Results from these studies have been used to deduce how these drugs interact with phosphatidylcholine bilayers. The emission energy, fluorescence quantum yield and lifetime exhibited a biphasic dependence on solvent polarity. In aprotic solvents, alcohols and in ethanol-water mixtures containing less than 40% water, quantum yields and lifetimes were high (approximately 0.55 and 8.5 ns respectively). In ethanol-water mixtures containing >40% water, the strong fluorescence quenching was primarily due to an increase in the rate of non-radiative deactivation of the excited state. Both the radiative ( k_r ) and non-radiative ( k_nr ) rate constants show a biphasic dependence on solvent polarity. These studies suggest the presence of two singlet excited states for these molecules, a polar singlet excited state, S_1-p and a charge transfer excited state, S_1-ct with the latter predominating in ethanol-water mixture containing >40% water. In egg phosphatidylcholine bilayers, the fluorescence, lifetime and quantum yield are consistent with the view that these drugs are localized within the lipid head group region where the charge-transfer excited state can be stabilized by intermolecular hydrogen bonding.     

Synthesis and characterization of fluorescent pyrrolyldipyrrinato Sn(IV) complexes

A series of neutral, 5-coordinate pyrrolyldipyrrinato Sn(IV) complexes have been synthesized via reaction of a pyrrolyldipyrrin, or its corresponding hydrochloride salt, with dibutyltin or diphenyltin oxide. The complexes are structurally unique in that all three nitrogen atoms of the pyrrolyldipyrrinato ligand bind to the tin center, making these complexes the first examples of pyrrolyldipyrrins behaving as LX(2) ligands. The complexes are highly fluorescent, exhibiting fluorescence quantum yields between 0.28 and 0.61, and display interesting preliminary biological activity.     

疏水作用对光化学和光物理过程的影响II: 不良溶剂中长链水杨酸烷基酯的簇集和荧光光谱的变化

本文报道证明长链分子在不良溶剂中发生簇集的实验事实.长链水杨酸烷基酯在二甲基亚砜-水(DMSO-H2O)和乙二醇-水(EG-H2O)混合溶剂中的荧光光谱分布以及荧光量子产率与短链水杨酸烷基酯的显著不同,这些差别可以用长链分子发生簇集来加以解释.     

FLUORESCENCE PROPERTIES OF ETHENOTHIAMINE*

Abstract— The absorption and fluorescence properties of ethenothiamine in neutral and acidic solution are reported, and some are found to be in contradiction to previous findings. The low fluorescence quantum yields of ethenothiamine make it a poor substitute for the vitamin in biological systems.     

含吡啶环的芳香醚-噁二唑类化合物的合成及其光谱研究

为开发新的高强度的有机电致发光材料, 用含烷氧基的取代苯甲酸(2)与2,6-吡啶二甲酰肼(3)在POCl3作用下, “一锅煮”法合成6个结构对称的含吡啶环的芳香醚-噁二唑4a～4f. 通过MS, IR, 1H NMR, 元素分析等手段对其结构进行了表征. 化合物的荧光性能测定结果显示此类化合物具有良好的荧光性, 其荧光发射波长均在347～507 nm范围内, 最大荧光发射波长在384 nm附近处, 且荧光强度较强. 在芳环上引入5-Br基团(4e, 4f), 化合物的荧光发射波长发生红移, 荧光强度有所减弱. 以硫酸奎宁作参比, 测定6个目标产物的荧光量子产率, 5-Br基团的引入对荧光量子产率没有明显影响. 同时讨论了代表性产物4a在不同溶剂中最大荧光激发波长处的荧光量子产率, 发现溶剂极性对该类化合物的荧光量子产率基本没有影响.     

Systematic atomic number effects in complexes exhibiting ligand luminescence: Part 2. Salicylidene-o-aminophenolates

The room-temperature fluorescence properties of Group IIIA metal complexes with salicylidene-o-aminophenol (SoAP) in aqueous 20% methanol are reported. The data include absorption, emission and excitation maxima, quantum yields and luminescence lifetimes. A systematic heavy atom effect influences the fluorescence decay to an extent sufficient for simultaneous kinetic analysis of ternary metal ion mixtures, based on decayrate measurements.     

反-1,2-双[2-(5-取代苯基恶唑基)]环丙烷的合成与光性能的研究

合成了8个反 -1,2-双[2-(5-取代苯基恶唑基)]环丙烷和2个1,2-双[2-取代苯基恶唑基)]乙烷,其中9个为新化合物.讨论了化合物的结构与其电子光谱及荧光量子产率间的关系.发现恶唑环与三元环间存在一定程度的共轭,并解释了上述化合物荧光量子产率较低的现象.     

Photophysicochemical and fluorescence quenching studies of benzyloxyphenoxy-substituted zinc phthalocyanines

Photochemical and photophysical measurements were conducted on peripheral and non-peripheral tetrakis- and octakis(4-benzyloxyphenoxy)-substituted zinc phthalocyanines (1, 2 and 3). General trends are described for photodegradation, and fluorescence quantum yields, triplet lifetimes and triplet quantum yields as well as singlet oxygen quantum yields of these compounds in dimethylsulphoxide (DMSO) and toluene. The fluorescence of the complexes is quenched by benzoquinone (BQ), and fluorescence quenching properties are investigated in DMSO and toluene. The effects of the solvents on the photophysical and photochemical parameters of the zinc(II) phthalocyanines (1, 2 and 3) are also reported. Photophysical and photochemical properties of phthalocyanine complexes are very useful for PDT applications.     

Fluorescent Molecular Probes II. The Synthesis, Spectral Properties and Use of Fluorescent Solvatochromic Dapoxyl Dyes

Abstract— 2,5-Diphenyloxazoles that embody a dimethylamino group at position 4 of the 5-phenyl ring and a sulfonyl group at position 4 of the 2-phenyl ring were prepared as new fluorescent solvatochromic dyes. In these molecules, there is a "push-pull" electron transfer system from the 5-phenyl moiety to the 2-phenyl ring. These compounds show strong solvent-dependent fluorescence that is well correlated with the empirical solvent polarity parameter ET (30). The solvent polarity dependence suggests that the fluorescence arises from an intramolecular charge transfer. The fluorescence-environment dependence, long emission wavelength, large extinction coefficients, high fluorescence quantum yields and large Stokes shift of the fluorophores can be used to develop ultrasensitive fluorescent molecular probes to study a variety of biological events and processes.     

Insights into the AIEE of 1,8‐Naphthalimides (NPIs): Inverse Effects of Intermolecular Interactions in Solution and Aggregates

Systematic structural perturbation has been used to fine‐tune and understand the luminescence properties of three new 1,8‐naphthalimides (NPIs) in solution and aggregates. The NPIs show blue emission in the solution state and their fluorescence quantum yields are dependent upon their molecular rigidity. In concentrated solutions of the NPIs, intermolecular interactions were found to quench the fluorescence due to the formation of excimers. In contrast, upon aggregation (in THF / H₂O mixtures), the NPIs show aggregation‐induced emission enhancement (AIEE). The NPIs also show moderately high solid‐state emission quantum yields (ca. 10–12.7 %). The AIEE behaviour of the NPIs depends on their molecular rigidity and the nature of their intermolecular interactions. The NPIs 1 – 3 show different extents of intermolecular (π–π and C?H???O) interactions in their solid‐state crystal structures depending on their substituents. Detailed photophysical, computational and structural investigations suggest that an optimal balance of structural flexibility and intermolecular communication is necessary for achieving AIEE characteristics in these NPIs.     

反-1,2-双[2-(5-取代苯基恶唑基)]环丙烷的合成与光性能的研究

本文合成了8个反-1,2-双[2-(5-取代苯基恶唑基)]环丙烷和2个1,2-双[2-(5-取代苯基恶唑基)]乙烷,其中9个为新化合物。讨论了化合物的结构与其电子光谱及荧光量子产率间的关系。我们发现恶唑环与三元环间存在一定程度的共轭,并解释了上述化合物荧光量子产率较低的现象。     

Spectroscopic properties of anisole in mixed polar solvents

Absorption and emission spectra, fluorescence quantum yields and lifetimes were studied for anisole in binary ethanol-water mixtures. The spectroscopic and photophysical properties show an exceptional behaviour in the aqueous solution. In water a strong nonradiative process, originating from the fluorescent state decreases the emission yield and lifetime. The results are discussed in terms of short range interactions between the solute and solvent.     

THE PHOTOPHYSICAL CONSTANTS OF SEVERAL FLUORESCENT DYES PERTAINING TO ULTRASENSITIVE FLUORESCENCE SPECTROSCOPY

Abstract— The successful implementation of ultrasensitive fluorescence spectroscopy of biological and chemical species depends upon certain photophysical parameters associated with the fluorescent dye used in the investigation. These parameters include the fluorescence quantum efficiency, photodestruction quantum efficiency, absorption cross section and fluorescence lifetime. These photophysical constants were measured for several fluorescent dyes that are used for the tagging of biological species. Three different solvents, ethanol, water and a cationic surfactant used above its critical micelle concentration, were studied. The effective photon yield (ratio of the fluorescence quantum yield to the photodestruction quantum efficiency) for the dyes is nearly 100 times greater in ethanol than it is in water because of the superior photostabilities of these dyes in ethanol solvents. The implications of these parameters for the design of an ultrasensitive fluorescence experiment are discussed.     

Synthesis, photophysical and photochemical properties of poly(oxyethylene)-substituted zinc phthalocyanines

The synthesis, photophysical and photochemical properties of the tetra- and octa-poly(oxyethylene)substituted zinc (II) phthalocyanines are reported for the first time. The new compounds have been characterized by elemental analysis, IR, 1H and 13C NMR spectroscopy, electronic spectroscopy and mass spectra. General trends are described for photodegradation, singlet oxygen, triplet state and fluorescence quantum yields, and triplet and fluorescence lifetimes of these compounds in dimethylsulfoxide (DMSO). Photophysical and photochemical properties of phthalocyanine complexes are very useful for PDT applications. The effects of the substituents on the photophysical and photochemical parameters of the zinc(II) phthalocyanines (3a, 5a and 6a) are also reported. The singlet oxygen quantum yields (Phi(Delta)), which give an indication of the potential of the complexes as photosensitizers in applications where singlet oxygen is required (Type II mechanism) ranged from 0.60 to 0.72. Thus, these complexes show potential as Type II photosensitizers. The fluorescence of the complexes was quenched by benzoquinone (BQ).     

PUVA-Induced Cell Mortality in NCTC 2544 Keratinocytes: Is It Related to the Microenvironmental Properties of the Excited States of Psoralens?

The phototoxic effect of psoralen (PSO), 5-methoxypsoralen (5MOP), 8-methoxypsoralen (8MOP) and 4,5',8-trimethylpsoralen (TMP) has been compared on the NCTC 2544 keratinocyte cell line in terms of cell mortality and lipid peroxidation. The order of effectiveness for cell photokilling is TMP, 5MOP >> 8MOP, PSO, whereas a little lipid peroxidation is observed for the four psoralens under study. Oxygen-independent membrane damage seem to play a key role in the lethal photodamage because the biological effectiveness of the most hydrophobic lipid-soluble psoralens, TMP and 5MOP, is about an order of magnitude higher than that of the more water-soluble 8MOP and PSO. In relation to this hypothesis, and in contrast to 8MOP, TMP is readily extracted from cells by ethyl acetate, a good membrane solvent, as shown by GC/MS analysis on cell extracts. The results are discussed in terms of the highly microenvironment-dependent photophysical properties of psoralens. By the measure of the intracellular psoralen concentration, the neutral red uptake and the lipid peroxidation products, this work provides evidence that PUVA therapy-mediated cell mortality is a lipid peroxidation-independent phenomenon.     

THE PHOTOPHYSICS OF MEROCYANINE 540. A COMPARATIVE STUDY IN ETHANOL AND IN LIPOSOMES

Abstract— Absorption and fluorescence emission spectra, fluorescence lifetimes, fluorescence quantum yields, photoisomerization quantum yields and triplet quantum yields were measured for Merocyanine 540 (MC540) in ethanol and in large unilamellar dimyristoyl phosphatidylcholine vesicles. The major differences in the photophysics between the two media are the increase of the fluorescence quantum yield from 0.15 in ethanol to 0.6 in vesicles at 25° C, and the appearance of a second fluorescence decay with a lifetime of 1.87 ns in the latter medium. Upper and lower limits for the photoisomerization quantum yields were determined by combining the data from laser flash photolysis and optoacoustic spectroscopy. The decrease in photoisomerization quantum yield upon incorporation of the dye into the lipid bilayer by a factor 2 suggests that this process competes directly with fluorescence. The temperature dependence of the fluorescence and photoisomerization quantum yields in solution supports this model. In both media MC540 has a very low triplet quantum yield with values 0.002 > (> ø_T > 0.02 in ethanol and 0.01 > ø_T- > 0.09 in liposomes Our data are consistent with the model whereby the dye is incorporated into the lipid bilayer as a monomer with two different orientations and this model is adopted on the basis of the biexponential behaviour of the fluorescence and photoisomer decay.     

Spectral luminescence properties of 1- and 2-alkyl(cycloalkyl) derivatives of benzo[f]quinoline

The absorption and fluorescence spectra of alcohol solutions of 3-aryl-substituted benzo[f]-quinolines were investigated, and the fluorescence quantum yields were measured. It was established that the indicated compounds have intense absorption in the UV region and fluorescence at 350–450 nm. The fluorescence quantum yields range from 5 to 70%, depending on the substituents. The introduction of aromatic substituents in the 1 and 3 positions of benzo-[f]quinoline ring raises the fluorescence quantum yields. A methyl group in the 2 position of the molecule leads to a decrease in the fluorescence quantum yield. Benzo[f]quinoline derivatives that contain a cyclopentene ring in the 1 and 2 positions fluoresce intensely (=40–60%), while cyclohexene and cycloheptene condensed in the same positions cause a decrease in the fluorescence yield to 7–13%; this is associated with the three-dimensional structure of these molecules.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1237–1240, September, 1977.     

Effect of the solvent composition in methanol-pentane and methanol-acetonitrile mixtures on the spectral and luminescent properties of 1,2-dihydroquinolines

The dependence of absorption and fluorescence spectra, quantum yields, and lifetimes of fluorescence on the solvent composition in the MeOH-C₅H₁₂ and MeOH-MeCN mixtures was studied for 2,2,4,6-tetramethyl-1,2-dihydroquinoline (TMDHQ). The variations in the parameters of deconvolution of the absorption and fluorescence spectra by the Gaussian functions in the MeOH-C₅H₁₂ mixtures of various compositions indicate the specificity of methanol clustering in saturated hydrocarbons and hydrogen bonding between TMDHQ and the methanol clusters of different compositions. At low MeOH concentrations (∼0.2 vol %), TMDHQ molecules are practically completely bound with the MeOH molecules by hydrogen bonds. In the MeOH-MeCN mixtures, the changes in the absorption and fluorescence spectra are observed at a substantially higher MeOH concentration (≥10 vol %) and monotonically change at the further increase in the MeOH concentration that is caused by the peculiarities of MeOH clustering in acetonitrile and the distribution of the TMDHQ molecules between the solvent components. At 50–95 vol % of MeOH in the mixture with MeCN, the fluorescence decay kinetics is described by the biexponential curve with the lifetime of the major component (τ₁) decreasing from 7.5 to 1.1 ns in pure MeCN and MeOH, respectively, and the lifetime of the minor component τ₂ ≈ 4 ns corresponding to the fluorescence lifetime in the solution containing 50 vol % MeOH. This indicates the existence of the free TMDHQ molecules, which are not bound with MeOH molecules or their clusters.     

Solvent Effect on the Spectral Characteristics and Quantum Yields of the Photolysis of Alkylated 1,2-Dihydroquinolines

On the basis of spectral data and the reaction of photolysis and fluorescence quantum yields in different pure solvents and solvent mixtures, it has been concluded that hydrogen bonding between 1,2-dihydroquinolines (DHQs) and a solvent, where the solvent is a proton donor, plays the key role in the reaction of photoinduced solvent addition to the DHQ double bond. The high sensitivity of DHQ photolysis to the solvent composition was shown, allowing us to suggest this reaction as a probe for studying the microenvironment of related compounds in mixtures.