Synthesis, Characterization, Optical Properties and Theoretical Studies of Novel Substituted Imidazo[1,5-a]pyridinyl 1,3,4-Oxadiazole Derivatives

Novel imidazo[1,5-a]pyridinyl 1,3,4-Oxadiazole derivatives were synthesized and characterised by IR, ¹H NMR and HRMS.UV-vis absorption and fluorescence properties of these compounds in different solutions showed that the maximal emission wavelength was not significantly changed in different solvents; however, maximum absorption wavelength was blue-shifted with the increase of solvent polarity. Absorption λ_max and emission λ_max was less correlated with substituent groups on benzene rings. The calculated molecular orbital correlates well with their absorption.     

Synthesis,X-Ray Crystal Structures and Optical Properties of Novel Substituted Pyrazoly 1,3,4-Oxadiazole Derivatives

Novel pyrazoly 1,3,4-oxadiazole derivatives were synthesized and characterized by ¹H NMR, IR, HRMS and X-ray diffraction analysis. UV–vis absorption and fluorescence properties of these compounds in different solutions showed that the maximum absorption wavelength was not significantly changed in different solvents; however, maximal emission wavelength was red-shifted with the increase of solvent polarity. Absorption λ_max and emission λ_max was less correlated with substituent groups on aryl rings.     

New Fluorescent Sensors Based on 1<Emphasis Type="Italic">H</Emphasis>-pyrazolo[3,4-<Emphasis Type="Italic">b</Emphasis>]quinoline Skeleton

Novel fluorescing dyes 1,3,4-triphenyl-6-(1,4,7,10-tetraoxa-13-aza-cyclopentadec-13-ylmethyl)-1H-pyrazolo[3,4-b]quinoline (K1) and 2-[(2-hydroxyethyl)-(1,3,4-triphenyl-1H-pyrazolo[3,4-b]quinolin-6-ylmethyl)-amino]ethanol (L1) have been synthesized and investigated by the means of steady state and time-resolved fluorescence techniques. These compounds act as sensors for the fluorescence detection of small inorganic cations (lithium, sodium, barium, magnesium and calcium) in solvents of different polarities (THF and acetonitrile). The mechanism, which allows application of these compounds as sensors, is an electron transfer from the electro-donative part of molecule to the acceptor part (fluorophore), which is retarded upon complexation of the electro-donative part by inorganic cations. We found that crown ether-containing compound is very sensitive to the addition of any investigated ions but amino alcohol-containing one exhibits better selectivity to the addition of two-valued cations. Two kinds of the complexes (LM⁺ and L₂M⁺) were found in the investigated systems. In addition, the dyes may be used as fluorescence indicators in solvents of lower polarity like tetrahydrofuran.     

Solvatochromic Studies of Fluorescent Azo Dyes: Kamlet-Taft (π*, α and β) and Catalan (Spp, SA and SB) Solvent Scales Approach

A new metal ion-responsive azo-based fluorescent probes have been synthesized and characterized by NMR spectral techniques. Steady-state fluorometric study has been used to analyze the spectroscopic and photophysical characteristics of dye derivatives in various solvents. The fluorescence properties of these dyes are strongly solvent dependent, the wavelength of maximum fluorescence emission shifts to the red. The Kamlet-Taft and Catalan’s solvent scales were found to be the most suitable for describing the solvatochromic shifts of the absorption and fluorescence emission. The hydroxy substituted azo dye formed complexes with several metal ions (Co²⁺, Hg²⁺, Ni²⁺ and Cu²⁺) and fluorescence quenching with metal ions reveal that it can be used as a new fluorescence sensor to detect the Cu²⁺ ion.     

Bay Functionalized Perylenediimide with Pyridine Positional Isomers: NIR Absorption and Selective Colorimetric/Fluorescent Sensing of Fe<Superscript>3+</Superscript> and Al<Superscript>3+</Superscript> Ions

Bay functionalized perylene diimide substituted with pyridine isomers, (2-pyridine (2HMP-PDI), 3-pyridine (3-HMP-PDI) and 4-pyridine (4-HMP-PDI)) have been synthesized and explored for selective coloro/fluorimetric sensing of heavy transition metal ions. HMP-PDIs showed strong NIR absorption (760–765 nm) in DMF. The absorption and fluorescence of HMP-PDIs have been tuned by make use of pyridine isomers. Reddish-orange color was observed for 2-HMP-PDI (λ_max = 437, 551, 765 nm) whereas 4-HMP-PDI exhibited light green (λ_max = 432, 522, 765 nm). 3-HMP-PDI showed orange-yellow (λ_max = 431, 524, 762 nm). The fluorescence spectra of 2-, 3- and 4-HMP-PDI showed λ_max at 585, 538, 546 nm, respectively. Interestingly, HMP-PDI dyes showed selective color change (intense pink color) and fluorescence quenching for Fe³⁺ and Al³⁺ metal ions in DMF. Absorbance spectra revealed complete disappearance of NIR absorption and intensification/appearance of new peak at lower wavelength. The concentration dependent studies suggest that 4-HMP-PDI can detect up to 36.52 ppb of Fe³⁺ and 43.12 ppb of Al³⁺ colorimetrically. The interference studies in presence of other metal ions confirmed the good selectivity for Fe³⁺ and Al³⁺. The mechanistic studies indicate that Lewis acidic character of Fe³⁺ and Al³⁺ ions were responsible for selective color change and fluorescence quenching.     

Investigation of Solvent Effects on Photophysical Properties of New Aminophthalimide Derivatives-Based on Methanesulfonate

Novel aminophthalimide derivatives were synthesized starting from (3aR,7aS)-2-(2-hydroxypropyl)-3a,4,7,7a–tetrahydro-1H-isoindole-1,3(2H)-dione (9) , and solvent effects on the photo-physical properties of these newly synthesized aminophthalimide derivatives (compounds 14 and 15) were investigated using UV-Vis absorption spectroscopy, steady-state and time-resolved fluorescence measurements. Both absorption and fluorescence spectra exhibited bathochromic shift with the increased polarity of the solvents for both molecules. Solute-solvent interactions were analyzed using the Lippert-Mataga and Bakhshiev polarity functions, and Kamlet-Taft and Catalan multiple linear regression approaches. The results revealed that these two molecules experienced specific interactions. Furthermore, photo-physical parameters were calculated for both molecules in all of the solvents, such as the fluorescence quantum yield, fluorescence lifetime, radiative (k_r) and non-radiative (k_nr) rate constant values. It was observed that the fluorescence quantum yield values decreased linearly with increasing solvent polarity. This study proved the new dyes including isopropyl methanesulfonate group displayed different behavior from previous studies of aminophthalimide derivatives in water. It was recommended that these new dyes having interesting properties by changing solvent can be used various applications such as environmentally sensitive fluorescent probes, labels in biology, laser industry.     

Fluorescence of N,N-di(2-carboxyethyl)-<Emphasis Type="Italic">p</Emphasis>-anisidine in solution and crystalline states

The fluorescence properties of N,N-di(2-carboxyethyl)-p-anisidine (I) in solvents of various nature and in the crystalline state have been studied at room temperature (273 K) and at the boiling point of liquid nitrogen (77 K). Fluorescence in aqueous solutions of I with protonated (λ _ex /λ _fl ^max = 225/290 nm) and unprotonated (λ _ex /λ _fl ^max = 270/380 nm) amino nitrogen has been detected. On going from aqueous solutions to nonaqueous, the fluorescence band of unprotonated I experiences a blue shift and its intensity rises. The fluorescence intensity of the band in aprotic polar solvents is higher than that in protic solvents. A linear dependence of the fluorescence intensity of deprotonated I on Cu(II) concentration (ranging from 1.0 to 5.0 mg/dm³) in aqueous solution has been found. The fluorescence intensity of I in aqueous solutions at 77 K and pH 1–6 has been shown to increase in the presence of Zn(II) (1–170 mg/dm³) and Cd(II) (2–330 mg/dm³) although a similar dependence is not observed at 293 K.     

Spectral-Luminescent Properties of Cationic Indotricarbocyanine Dyes in Cancerous Cells and Solutions

The spectral-luminescent properties of symmetrical indotricarbocyanine dyes with the same cation and different anions (Br^–, BF₄ ^–) in cancerous HeLa cells, an isotonic solution of NaCl, and organic solvents have been investigated. It is shown that when these dyes are present in cells in nontoxic concentrations, they are in a monomeric state, they are localized in the region with a low dielectric permeability, bonded to biological macromolecules, and do not make contact with an aqueous medium. It has been established for the first time that the molecules of the polymeric dyes are present in cells predominantly in the form of contact ion pairs, and in a dye with the Br^– anion the presence of free cations or solvately separated ionic pairs is revealed. It is shown that the shift of the ion equilibrium toward contact ion pairs for the dyes in the cells (as compared to the low-polarity organic solvents) can be due to the fairly high concentration of salts in the biosystem.     

Singlet and Triplet State Properties and Singlet Oxygen Yield of an Amino-Acyl-Quinoxalinone Yellow Dye

Amino-acyl-quinoxalinone yellow dyes are cyclised analogues of the yellow azomethine dyes developed for, and still used in, silver halide colour photography. Unlike image azomethine dyes, which are rapidly deactivated in their excited states by torsion about the azomethine bond, amino-acyl-quinoxalinone dyes have an interesting photophysics because torsion is not possible due to their cyclised structure. We report results from studies on singlet and triplet state properties, and singlet oxygen yields, of the yellow dye, 7-diethylamino-3-(2,2-dimethyl-propionyl)-5-methyl-1-phenyl-1H-quinoxalin-2-one, in polar and nonpolar solvents. The dye photophysics is characterised by a weak fluorescence, with a solvent dependent emission yield (Φ_F?≈?0.002–0.004), and short singlet state lifetime (τ_expt?≈?20–50 ps), both increasing by a factor of ≈2 in going from polar acetonitrile to non-polar dioxane as solvent. DFT ZINDO calculations show a transition involving significant electron transfer from the diethyl-amino group into the carbonyl region of the molecule. In solution, in the presence of oxygen, the triplet state decays almost exclusively by oxygen quenching, and singlet oxygen is produced in high yield (Φ_??≈?0.5–0.55). The triplet state absorbs across the 450–750 nm region with maxima around 480 and 650 nm, and moderate molar absorption coefficients (ca. 6000–8000 M^?1 cm^?1). In a glass at 77 K, triplet decay gives a red phosphorescence, with λ_max?≈?640–650 nm, and a ?≈?0.25 s lifetime. If singlet oxygen yields are a good indication of triplet yields, then internal conversion and intersystem crossing occur with roughly equal efficiency.

     

Dual fluorescence and laser emissions from fluorescein-Na and eosin-B

Dual laser emissions were observed from fluorescein-Na and eosin-B in ethanolic solutions individually in the concentration range from 10⁻² to 10⁻³ mol dm⁻³ under N₂ laser excitation. The first compound was found to lase at two distinct regions with wavelength maxima around 540, 550 nm, while the second one around 558, 574 nm. Steady-state absorption, fluorescence excitation, fluorescence polarization, fluorescence emission and decays of the dyes in various solvents under varying conditions of excitation and detection systems were carried out to identify the nature of the emitting species responsible for laser emissions in two distinct regions. Both the dyes exhibited concentration and excitation wavelength dependence of fluorescence and the effects were found to be more pronounced in binary solution. The fluorescence decays of dyes were monoexponential in ethanol, while in some other solvents used, the decays showed biexponential behavior. The absorption and excitation studies using thin layers of solutions revealed the formation of dimers with the dye concentration around 1×10⁻³ mol dm⁻³. Fluorescence polarization and decay studies confirmed the presence of dimers. The two laser bands observed in the shorter and longer wavelengths were respectively ascribed to monomeric and dimeric species.     

Fluorescence Enhancement and Photostability of Novel Pentamethine Cyanines in Nafion-Na+ Membranes

Four novel pentamethine cyanines have been investigated for their photophysical behaviors and photochemical stability in Nafion-Na⁺ membranes. The incorporation processes of these dyes into Nafion membranes are diffusion-controlled and the apparent diffusion constants have been determined. Fluorescence quantum yields and fluorescence lifetimes of all tested dyes in Nafion membranes have been determined and significant fluorescence enhancements were observed with respect to their fluorescence in aqueous solution. Photolysis of these dyes suggested these dye molecules are stabilized significantly by Nafion membranes. Furthermore, the fluorescence enhancements and the photostabilization of these dyes are more significant in dry Nafion membranes than those in wet ones.     

Photodynamics of intramolecular proton transfer in polar and nonpolar biflavonoid solutions

Using methods of steady state luminescence and femtosecond spectroscopy, we have studied the mechanism of intramolecular proton transfer in synthesized 3,7-dihydroxy-2,8-di(4-methoxyphenyl)-4H,6H-pyrano[3,2-g]chromen-4,6-dion in polar and nonpolar solutions, films, and polycrystals at 293 and 77 K. In an excited singlet state, intramolecular proton transfer occurs in two stages. At the first stage, a tautomer with one transferred proton (OTP tautomer) is formed from the Franck-Condon state within ??₁ = 0.6 ps. At the second stage, the second proton is transferred within ??₂ = 3.1 ps and a tautomer with two transferred protons (TTP tautomer) is formed, which fluoresces in toluene at 293 K with a high quantum yield, ?? _f = 0.66, and the fluorescence spectrum of which is characterized by a large Stokes shift, 9900 cm^?1. At 293 K, polar solvents (dimethylformamide, dimethyl sulfoxide, ethanol, etc.) solvate the BFV molecule in the ground state, while, in the excited state, an OTP tautomer is mainly formed. In polar ethanol at 77 K, a dual fluorescence spectrum is observed, which is caused by the fluorescence emission of polysolvates with ?? _max ^f = 460 nm and TTP phototautomers at ?? _max ^f = 610 nm.     

Spectroscopic Study of the Interaction of Styrylcyanine Dyes Sbo,Sil and Their Derivatives with Bovine Serum Albumin

The spectral-luminescent characteristics of newly synthesized styrylcyanine dyes on the base of dyes Sbo ((E)-2-(4-(dimethylamino)styryl)-3-methylbenzo[d]oxazol-3-ium iodide) and Sil ((E)-2-(4-(dimethylamino)styryl)-1,3,3-trimethyl-3H-indolium perchlorate) in aqueous solutions without and in the presence of bovine serum albumin (BSA) were studied. It was established that the absorption spectra of dyes Tol-6, Dbo-10 and Dil-10 with increasing amount of BSA appear new bands with λ_max = 505 nm, λ_max = 512 nm and λ_max = 566 nm, respectively, whose intensity increases in proportion to the amount of albumin. The intensity of the glow of the main band of fluorescence in the presence of BSA sharply increases. The binding constant (K) and the number of binding sites (N) of studied dyes with BSA were determined. The dependence of binding constants with BSA on the dipole moment of dye molecules was determined, which indicates that besides electrostatic forces of attraction between molecules styrylcyanine dyes with BSA, hydrophobic interactions are essential.     

pH-Responsive Biocompatible Fluorescent Core-Shell Nanogel for Intracellular Imaging and Control Drug Release

This study reports a fluorescence iron core-carbonized biocompatible hybrid poly(ethylene glycol) (PEG)-oriented nanogel (Fe₂O₃@C@PEG-COOH nanogel). The fluorescence Fe₂O₃@C@PEG-COOH nanogel is prepared using a facile one-pot polycondensation reaction without organic solvents or catalysts. The properties of the fluorescenceFe₂O₃@C@PEG-COOH nanogel are investigated by fluorescence spectroscopy, transmission electron microscopy, X-ray diffraction, and thermogravimetric analysis. A change in pH as a stimulus can trigger the release of loaded doxorubicin (DOX). Under acidic conditions, the nanogel releases the highly loaded drug slowly compared to the neutral and basic conditions, which is important for cancer treatment. The synthesized fluorescenceFe₂O₃@C@PEG-COOH nanogel is well dispersed in water and shows fluorescence with high photostability, good biocompatibility with a paramagnetic nature. Furthermore, the nanogel can act as a potential fluorescent probe for cell imaging.     

Electronic structure and fluorescent properties of malononitrile-based merocyanines with positive and negative solvatochromism

The behavior of the positions and shapes of the fluorescence bands of di-, tetra-, and hexamethine merocyanine dyes with 3H-indolyliden (dyes 1–3) and benzoimidazolyliden (dyes 4–6) as electron-donating substituents and malononitrile as an electron-accepting substituent is studied by the method of moments in solvents of different polarity. The solvatofluorochromic shifts have been found to be smaller than the solvatochromic shifts not only for negatively solvatochromic merocyanines 4–6, but also for dyes 1–3 whose solvatochromism is positive. For dyes 4–6, cases of a change of the sign of solvatofluorochromism with respect to the sign of solvatochromism are revealed. These nontrivial effects are accounted for by transitions between the polyene and polymethine electronic structures of merocyanines in the fluorescence state S ₁ that occur with increasing medium polarity. In contrast to the absorption spectra of merocyanines 1–3, an increase in the chain length results in an increase in the vinylene shifts in the fluorescence spectra of these dyes, as well as in a decrease in the deviations and in the narrowing of the bands. This is explained by the fact that the electronic structure of these merocyanines in the S ₁ state is closer to that of the ideal polymethine (the cyanine limit) than in the S ₀ state. The fluorescence bands of merocyanines 4–6 are observed to be broader compared to the absorption bands. This broadening is caused by a change in the relation between intermolecular and vibronic interactions during absorption and emission of light. The interactions of these types have a decisive effect on the behavior of the Stokes shifts and fluorescence quantum yields of merocyanines 1–6.     

Water Soluble Metallo-Phthalocyanines: The Role of the Functional Groups on the Spectral and Photophysical Properties

Strategies are reported that produce symmetrical metal-free and metallo-phthalocyanine dyes, Pc and MPc, respectively, containing various numbers of water solubilizing carboxylic acid groups on their periphery that provide a dual role by also serving as functional groups to covalently link primary amine-containing targets to these dyes. In order to induce water compatibility and to minimize the degree of aggregation, the periphery of the macrocycle was decorated with various numbers of water-solubilizing groups and/or altering the identity of the metal center. The influence of the number of solubilizing groups and metal center on the spectral and photophysical properties were evaluated. MPc dyes containing 4, 8, or 16 carboxylic acid groups exhibited similar absorption and emission maxima (677 and 686 nm, respectively) with the molar absorptivity of the Q-band ∼10⁵ M⁻¹ cm⁻¹. Results indicated that the fluorescence lifetimes and quantum yields varied as a function of the metal center; the degree of carboxylation did not significantly alter these properties in DMSO, but did mediate the solubility and aggregation states when placed in aqueous solvents. The water solubilizing groups could also serve as labeling moieties for targets bearing primary amines. Results showed that the conjugate, produced by covalently linking an MPc to streptavidin through one of its carboxylate groups, generated a red-shift in the emission maximum with a fluorescence lifetime shorter than that of the native MPc dye.     

Novel,Monomeric Cyanine Dyes as Reporters for DNA Helicase Activity

The dimeric cyanine dyes, YOYO-1 and TOTO-1, are widely used as DNA probes because of their excellent fluorescent properties. They have a higher fluorescence quantum yield than ethidium homodimer, DAPI and Hoechst dyes and bind to double-stranded DNA with high affinity. However, these dyes are limited by heterogeneous staining at high dye loading, photocleavage of DNA under extended illumination, nicking of DNA, and inhibition of the activity of DNA binding enzymes. To overcome these limitations, seven novel cyanine dyes (Cyan-2, DC-21, DM, DM-1, DMB-2OH, SH-0367, SH1015-OH) were synthesized and tested for fluorescence emission, resistance to displacement by Mg²⁺, and the ability to function as reporters for DNA unwinding. Results show that Cyan-2, DM-1, SH-0367 and SH1015-OH formed highly fluorescent complexes with dsDNA. Of these, only Cyan-2 and DM-1 exhibited a large fluorescence enhancement in buffers, and were resistant to displacement by Mg²⁺. The potential of these two dyes to function as reporter molecules was evaluated using continuous fluorescence, DNA helicase assays. The rate of DNA unwinding was not significantly affected by either of these two dyes. Therefore, Cyan-2 and DM-1 form the basis for the synthesis of novel cyanine dyes with the potential to overcome the limitations of YOYO-1 and TOTO-1.     

AIE Based Coumarin Chromophore - Evaluation and Correlation Between Solvatochromism and Solvent Polarity Parameters

A new class of red emitting extensively conjugated donor-π-acceptor type dyes bearing coumarin units have been synthesized by condensation of 7-(diethylamino)-2-oxo-2 H-chromene-3-carbaldehyde with different active methylenes. All the dyes are characterized by ¹H NMR, ¹³C NMR and HRMS spectroscopy. The photophysical behaviour and the relation between structure and properties of the coumarin “push–pull” derivatives were investigated experimentally. The dyes exhibited positive solvatochromism and solvatofluorism in solution of varying polarity. These coumarin dyes show aggregation induced emission properties with red emitting fluorescence. They show absorption in the range of 501–528 and emission in the range of 547–630 nm. We evaluated photophysical properties of coumarin dyes using solvotochromism and solvent dependent shift in the emission wavelength. All the synthesized coumarin dyes COS1-COS4 are showing very good solvatochromic properties.     

Synthesis of Novel Carbazole based Styryl: Rational Approach for Photophysical Properties and TD-DFT

The synthesis and solvatochromic behavior of four novel carbazole based fluorescent styryl dyes were explained. In chlorinated solvents such as DCM and chloroform, these dyes show bathochromic shift in their absorption as well as emission. The styryl dyes 6b and 6c show solid state yellow fluorescence. DFT and TD-DFT computations were performed to study structural, molecular, electronic and photophysical properties of these dyes. The computed absorption and emission wavelength values are found to be in good agreement with the experimental results. The photophysical properties of these 1-styryl carbazole dyes are also compared with the recently reported 3-styrl carbazole dyes. The unique behavior of dye 6d is well explained by its optimized geometry found in the excited state. Ratio of ground to excited state dipole moment of the synthesized novel styryl compounds were calculated by Bakhshiev and Bilot-Kawski correlations.     

Anti-stokes fluorescence of polymethine dyes excited by a titanium-sapphire laser

Fluorescence of symmetric polymethine dye solutions (λ _abs ^max ≈ 700 nm) upon anti-Stokes excitation by cw radiation of a titanium-sapphire laser (781 nm) is first investigated. A series of six compounds with analogous composition and spectral and luminescent properties is investigated. It is demonstrated that in addition to the anti-Stokes component, the Stokes component with a maximum at 820 nm (referred to the H-aggregates of initial dyes) is observed in the fluorescence spectra of solutions of the examined molecules when dye concentration increases to 10⁻³ M. Dependences of the anti-Stokes and Stokes component intensities on the exciting radiation power are obtained that confirm a linear excitation character. On examples of xanthene and polymethine dyes, the use of organic fluorophors for anti-Stokes laser cooling and some other possible applications of the anti-Stokes fluorescence are discussed. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 63–70, March, 2007.