Symmetrical Dyes Research Articles

Synthesis and Characterization of Multifunctional Symmetrical Squaraine Dyes for Molecular Photovoltaics by Terminal Alkyl Chain Modifications

Novel far-red sensitive symmetric squaraine (SQ) dyes with terminal alkyl chain modifications were designed, synthesized, and characterized, aiming towards imparting multifunctionalities such as photosensitization, dye aggregation prevention, and source of electrolyte components. The dye sensitizer SQ-80 with alkyl chain terminal modifications consisting of 1-methylimidazolium iodide was designed and synthesized as a new dye sensitizer for DSSCs based on symmetric SQ-4 without any terminal modification used as reference. Upon adsorption on the mesoporous TiO2 surface, SQ-80 demonstrated reduced dye aggregation and stronger binding to the TiO2 surface, leading to enhanced durability of DSSCs. Apart from the most common photosensitization behavior, the newly designed dye demonstrated multifunctionalities such as aggregation prevention and electrolyte functionality, utilizing iodine-based redox electrolytes in the presence and absence of I2 and LiI additives. In the absence of LiI and I2, a mixture of SQ-77 with alkyl chain terminal modifications consisting of iodide and SQ-80 demonstrated a photoconversion efficiency of 1.54% under simulated solar irradiation, which was about six times higher compared with the reference dye SQ-4 (0.24%) (having no alkyl chain terminal modification).

Synthesis of 1,3-Dibromopyrene as Precursor of 1-, 3-, 6-, and 8-Substituted Long-Axially Symmetric Pyrene Derivatives.

Pyrene derivatives bearing substituents at positions 1, 3, 6, and 8 find numerous applications, as exemplified by their use in lasers, sensors, and bioimaging probes. However, these derivatives typically have point-symmetric or short-axially symmetric structures, whereas long-axially symmetric derivatives remain underexplored because of the difficulty in obtaining their precursor, 1,3-dibromopyrene. To address this problem, we herein synthesized 1,3-dibromopyrene from 1-methoxypyrene in an overall yield (71 % over four steps) considerably exceeding those of existing methods. 1,3-Dibromopyrene was converted into 13OPA, a long-axially symmetric pyrene dye with electron-donor (alkoxy) groups at positions 1 and 3 and electron-acceptor (formyl) groups at positions 6 and 8. 13OPA exhibited photophysical properties distinct from those of its point-symmetric and short-axially symmetric isomers, featuring a broad and strongly redshifted absorption, strong fluorescence with reduced sensitivity to protic solvents, and small dipole moment change upon photoexcitation. The derivatization of 13OPA into a Schiff base and its functionalization via Lewis acid-base pairing were also demonstrated. Thus, our work expands the design scope of pyrene-based molecules, particularly those used as emitters.

Rigid symmetric Rhodamine fluorescent dyes as fast selective detection of aluminum and iron ions applied to cell imaging

Fluorescent probe molecules have the advantages of good selectivity, high sensitivity, and easy operation, which have attracted much attention. In this paper, a novel symmetric rhodamine fluorescent probe with structural rigidity was synthesized by a simple reaction using rhodamine 6G as raw material. And it was characterized by NMR and electrospray spray mass spectrometry. Single crystal was prepared by solvent evaporation method, which was the first single crystal of the compound reported domestically and internationally. Special spiral ring structures were observed inside the crystal. Among different competing cations, the probe exhibited high selectivity and good sensitivity towards Al3+ and Fe3+ metal ions. The limits of detection were 0.76 nM and 0.49 nM, respectively. In the presence of Al3+ and Fe3+, the solution changed from colorless to pink. At the same time, there was a significant shift in the UV–vis spectrum and fluorescence emission spectrum. The UV–vis absorption peak appeared at 530 nm, while the emission at 556 nm was turned on. In addition, biological experiments have shown that the RP probe has good membrane permeability and has the potential to detect Al3+ and Fe3+ in Hela cells.

Glycols as novel solvents for synthesis of squaraine dyes

Glycols are non-volatile, non-flammable solvents for efficient, facile, and environmentally benign syntheses of various types of symmetric and non-symmetric squaraine dyes, thus providing a viable alternative to conventionally used n-butanol/toluene system.

Dual-state emission and two-wavelength amplified spontaneous emission behaviors observed from symmetric dyes based on functionalized fluorene and benzotriazole units.

Structurally symmetric dyes using functionalized fluorenes and benzotriazole as the main building moieties have been synthesized and found to exhibit efficient dual-state emission (DSE) and interesting two-wavelength or dual amplified spontaneous emission (dual-ASE) behaviors in the solution phase, which may benefit the development of organic gain materials with dual-wavelength amplification.

Ru(II)-Cyanine Complexes as Promising Photodynamic Photosensitizers for the Treatment of Hypoxic Tumours with Highly Penetrating 770 nm Near-Infrared Light.

Light-activated treatments, such as photodynamic therapy (PDT), provide temporal and spatial control over a specific cytotoxic response by exploiting toxicity differences between irradiated and dark conditions. In this work, a novel strategy for developing near infrared (NIR)-activatable Ru(II) polypyridyl-based photosensitizers (PSs) was successfully developed through the incorporation of symmetric heptamethine cyanine dyes in the metal complex via a phenanthrimidazole ligand. Owing to their strong absorption in the NIR region, the PSs could be efficiently photoactivated with highly penetrating NIR light (770 nm), leading to high photocytotoxicities towards several cancer cell lines under both normoxic and hypoxic conditions. Notably, our lead PS (Ru-Cyn-1), which accumulated in the mitochondria, exhibited a good photocytotoxic activity under challenging low-oxygen concentration (2% O2) upon NIR light irradiation conditions (770 nm), owing to a combination of types I and II PDT mechanism. The fact that the PS Protoporphyrin IX (PpIX), the metabolite of the clinically approved 5-ALA PS, was found inactive under the same challenging conditions positions Ru-Cyn-1 complex as a promising PDT agent for the treatment of deep-seated hypoxic tumours.

Tunable Optical Properties and Self-Assemblies of a Water-Soluble Perimidinium Imide Dye

AbstractThe synthesis of unsymmetrically peri-annulated naphthalene dyes, perimidinium imides (PrIm), is reported. Compared with the symmetrical and popular analogous naphthalenediimide dyes, PrIm showed a red-shifted absorption maximum. The water-soluble dyes showed tunable self-assembly behaviors and optical properties. The dyes retain their photoluminescence properties in water.

Design and Synthesis of Novel Squaraine Dye with Highly Enhanced Far‐Red Fluorescence and its Interaction with a Model Protein

Novel amine‐functionalized symmetrical squaraine (SQ)‐dye and fluorescein isothiocyanate (FITC)–SQ–FITC dye conjugate are designed and successfully synthesized, followed by their structural and photophysical characterizations. Symmetrical SQ dye exhibits complete fluorescence quenching in polar solvents, which is explained by considering photoinduced electron transfer (PET) as a dominant quenching pathway. In contrast, FITC–SQ–FITC dye conjugate results in a decrease in an aggregation of both SQ and FITC units and about 47 times enhancement in the far‐red fluorescence appearing at 674 nm. This profound enhancement in the far‐red fluorescence is explained by the synergistic influence of suppression of aggregation‐induced quenching (ACQ) and PET. This newly designed FITC–SQ–FITC dye conjugate shows complete quenching of the far‐red fluorescence in phosphate buffer saline (PBS) owing to very strong dye aggregation, as confirmed by spectral absorption investigation. In PBS, it strongly interacts with bovine serum albumin (BSA) (Ka = 1.1 × 104 m−1) used as a model protein breaking the dye aggregation by BSA and increasing far‐red fluorescence associated with SQ as a function of increasing BSA concentration. A profound 117 times increase in fluorescence at 674 nm with 25 times of BSA concentration suggests that the designed FITC–SQ–FITC is an excellent far‐red probe for dye‐protein interaction.

Synthesis, optical, electrochemical, and computational investigation of new cyanopyridine-centered organic dyads

Herein we report the molecular design, synthesis, and inclusive investigation of four novel di-anchored symmetric dyes (CP1-4) centered on electron deficient cyanopyridine scaffold as possible photosensitizers for DSSC application. These new chromogens (CP1-4) comprise a powerful electron-withdrawing cyanopyridine moiety linked with additional electron attracting functionalities such as cyanoacetic acid (CP1), 3-(carboxymethyl) rhodanine (CP2), 2,4,6-pyrimidinetrione (CP3), and 2,6-dihydroxy-2-mercaptopyrimidine (CP4), as effective acceptor/anchoring units via biphenyl donor units. Their in-depth optical and electrochemical behaviour were investigated to assess their suitability as photosensitizers. Further, the molecular modeling calculations were undertaken to understand their ground state properties and energy level potentials. The comprehensive studies revealed that they own all the requisites to performance as a potential photosensitizer for DSSC application.

Aggregates of Cyanine Dyes: When Molecular Vibrations and Electrostatic Screening Make the Difference.

Aggregates of cyanine dyes are currently investigated as promising materials for advanced electronic and photonic applications. The spectral properties of aggregates of cyanine dyes can be tuned by altering the supramolecular packing, which is affected by the length of the dye, the presence of alkyl chains, or the nature of the counterions. In this work, we present a joint experimental and theoretical study of a family of cyanine dyes forming aggregates of different types according to the length of the polymethinic chain. Linear and nonlinear optical spectra of aggregates are rationalized here in terms of an essential-state model accounting for intermolecular interactions together with the molecular polarizability and vibronic coupling. A strategy is implemented to properly account for screening effects, distinguishing between electrostatic intermolecular interactions relevant to the ground state (mean-field effect) and the interactions relevant to the excited states (excitonic effects). To the best of our knowledge, this is the first attempt to simulate nonlinear spectral properties of aggregates of symmetric dyes accounting for molecular vibrations.

How Does Pseudo-Jahn-Teller Effect Induce the Photoprotective Potential of Curcumin?

In this paper, the molecular and electronic structure of curcumin is studied. High-symmetric gas-phase tautomers and their deprotonated forms in various symmetry groups are identified. The stability of lower-symmetry structures was explained by using the Pseudo-Jahn-Teller (PJT) effect. This effect leads to stable structures of different symmetries for the neutral enol and keto forms. The presented analysis demonstrated the potential significance of the PJT effect, which may modulate the setting of electronic and vibrational (vibronic) energy levels upon photodynamic processes. The PJT effect may rationalize the photoprotection action and activity of naturally occurring symmetric dyes.

Trimethine Cyanine Dyes as NA-Sensitive Probes for Visualization of Cell Compartments in Fluorescence Microscopy.

We propose symmetrical cationic trimethine cyanine dyes with β-substituents in the polymethine chain based on modified benzothiazole and benzoxazole heterocycles as probes for the detection and visualization of live and fixed cells by fluorescence microscopy. The spectral-luminescent properties of trimethine cyanines have been characterized for free dyes and in the presence of nucleic acids (NA) and globular proteins. The studied cyanines are low to moderate fluorescent when free, but in the presence of NA, they show an increase in emission intensity up to 111 times; the most pronounced emission increase was observed for the dyes T-2 in the presence of dsDNA and T-1 with RNA. Spectral methods showed the binding of all dyes to nucleic acids, and different interaction mechanisms have been proposed. The ability to visualize cell components of the studied dyes has been evaluated using different human cell lines (MCF-7, A2780, HeLa, and Hs27). We have shown that all dyes are cell-permeant staining nucleus components, probably RNA-rich nucleoli with background fluorescence in the cytoplasm, except for the dye T-5. The dye T-5 selectively stains some structures in the cytoplasm of MCF-7 and A2780 cells associated with mitochondria or lysosomes. This effect has also been confirmed for the normal type of cell line-human foreskin fibroblasts (Hs27). The costaining of dye T-5 with MitoTracker CMXRos Red demonstrates specificity to mitochondria at a concentration of 0.1 μM. Colocalization analysis has shown signals overlapping of dye T-5 and MitoTracker CMXRos Red (Pearson's Coefficient value = 0.92 ± 0.04). The photostability study shows benzoxazole dyes to be up to ∼7 times more photostable than benzothiazole ones. Moreover, studied benzoxazoles are less cytotoxic at working concentrations than benzothiazoles (67% of cell viability for T-4, T-5 compared to 12% for T-1, and ∼30% for T-2, T-3 after 24 h). Therefore, the benzoxazole T-4 dye is proposed for nucleic acid detection in vitro and intracellular fluorescence imaging of live and fixed cells. In contrast, the benzoxazole dye T-5 is proposed as a good alternative to commercial dyes for mitochondria staining in the green-yellow region of the spectrum.

Janus-Type AIE Fluorophores: Synthesis and Properties of π-Extended Coumarin-Bearing Triskelions.

Janus-type triskelion-shaped fluorophores comprising coumarins bearing various electron-donating substituents (1aad, 1add, 1ccd, and 1cdd) were successfully synthesized via an intramolecular Ullmann coupling. Density functional theory (DFT) calculations indicated that all the compounds presented two different molecular surfaces, similar to Janus-type molecules. The absorption and fluorescence spectra of asymmetrical derivatives 1aad, 1add, 1ccd, and 1cdd exhibited a bathochromic shift due to their narrow highest occupied molecular orbital (HOMO) -lowest unoccupied molecular orbital (LUMO) gap. Natural transition orbital (NTO) analysis indicated that the excited state orbital overlaps differ among the C3 symmetrical and asymmetrical dyes. These triskelion-shaped fluorophores were found to form molecular nanoaggregates in THF/H2O mixtures and demonstrated aggregation-induced emission (AIE) enhancement characteristics as a result of restricting their molecular inversion. These results indicate that Janus-type AIE fluorophores are potentially applicable as solid-state fluorescent chiral materials, which can be optimized by controlling their molecular rearrangement in the solid state.

Modeling the Effect of H-Bonding of Excited Quadrupolar Molecules with a Solvent on Charge Transfer Symmetry Breaking.

A model of the H-bonding effect on charge transfer symmetry breaking in excited quadrupolar dyes is proposed. A dye is assumed to have two symmetrically arranged H-bond acceptors. The effect of H-bonding is described in terms of two quantities: (i) the free energy of H-bond formation by an excited symmetric dye with a protic solvent and (ii) a parameter that determines the susceptibility of the H-bond strength to the charge of the H-bond acceptor. The model assumes that an increase in dye dissymmetry results in a charge shift from one acceptor to the other, making one acceptor more negative and the other less negative. As a result, the strength of the H-bond on one branch increases, while on the other branch, it decreases. An analytical solution of the mathematical model is obtained. Regardless of the strength of the H-bond, the effect of the H-bonding on the symmetry breaking degree is shown to be small, as long as the free energy of formation of the weaker H-bond is negative. A strong effect is expected only if this free energy becomes positive, that is, when the H-bond is formed on only one arm. An unexpected result of weakening of the dissymmetry degree caused by the strengthening of the H-bond is predicted and discussed. An approach for quantitative determination of the susceptibility of the H-bond strength to the charge of the H-bond acceptor is proposed.

Near‐Infrared Squaraine Dyes as Bright Fluorescent Probes: A Structure–Activity Photophysical Investigation in Liposomes

AbstractThe efficient investigation of biological membranes is a constant demand in chemical biology. Several families of Near Infra‐Red (NIR) dyes have been already studied for the selective staining of a plethora of biological structures, macro and supramolecular assemblies. In this context, a small library of symmetrical and unsymmetrical NIR squaraine dyes have been synthetized and investigated as fluorescent probes to stain the lipid bilayer membrane in large unilamellar vesicles (LUVs) as cell membrane model. The hydrophobic‐hydrophilic character of the NIR dyes has been modulated by introducing carboxylic moieties on the aromatic core, as well as by varying the length of the alkyl chains used in the quaternarization of the indolenine nitrogen. The photophysical properties and the kinetic of the insertion into different LUVs models have been analysed with respect to the probe structures. The discussed results represent versatile key data to support the design of new NIR sensors for bioimaging.

Luminescence spectral peculiarities of polymethine dye, bonded covalently to polyurethane matrix

Luminescence spectral properties of the two symmetrical indocyanine dyes with different substituents near nitrogen atoms have been investigated in the polyurethane matrices. The analysis of the IR-spectra, measured for the product of a reaction between indolenine salt, being a terminal heterocyclic fragment in one of these dye molecules, and phenyl isocyanate, and this salt and isocyanate as single bulk compounds has shown possibility of covalent bonding between this indocyanine and polyurethane. Such covalent bonding of the dye with the polymer matrix results in improvement of its luminescence spectral properties, compared to the dye-polymer solutions.

Effect of halide/pseudohalide anions on the association and semimicroextraction of substituted chloroaurates with a symmetric carbocyanine dye: A complex study and analytical application

The present work is focused on investigating the interaction of halide/pseudohalide-substituted chloroaurates with a symmetric carbocyanine dye 1,3,3-trimethyl-2-[5-(1,3,3-trimethyl-1,3-dihydroindol-2-yliden)-penta-1,3-dienyl]–3H-indolium chloride (DIDC), and on the optimization of formation and further semimicroextraction of Au ion associate for the spectrophotometric Au determination at 647 nm. Ligand changing in chloroaurates significantly improves the sensitivity and selectivity of the method. The molar absorptivity of the ion associates has been found in the range (10.7–15.6) × 10−4 L mol−1 cm−1, depending on the ligand. For the Au determination, a novel analytical system has been developed. The appropriate reaction conditions were found to be: the N3− ligand, pH 5.0, 5 × 10−5 mol L−1 of DIDC, amyl acetate as extraction solvent. The limit of detection (LOD) and limit of quantification (LOQ) were found to be 0.10 µg mL−1 and 0.31 µg mL−1 of Au, respectively. The proposed method was applied to the determination of gold in artificial and pharmaceutic samples with reliable results. QTAIM analysis of DIDC chloroaurates electron density calculated at the CPCM(water)-B3LYP/ma-def2-SVP level of theory allowed to build a selectivity row which correlates well with the experimental data.

CB[10]-driven self-assembly of a homotrimer from a symmetric organic dye: tunable multicolor fluorescence and higher solid-state stability than that of a CB[8]-included homodimer

A symmetric organic dye can form a highly stable homotrimer in the cavity of CB[10], which exhibits unique multicolour fluorescence different from that of the single molecule or its dimer.

Self-template biomass-derived nitrogen and oxygen co-doped porous carbon for symmetrical supercapacitor and dye adsorption

Self-template biomass-derived nitrogen and oxygen co-doped porous carbon for symmetrical supercapacitor and dye adsorption

Covalent bonding effects on spectral, photophysical and generation properties of indocarbocyanine dyes in polyurethanes

Spectral, photophysical and generation properties of symmetrical cationic cyanine dyes have been investigated in the polyurethane matrices, similar by the structure, but different by the polymerization method. The cyanine dye doped polyurethane, synthesized by a polycondensation reaction, provides laser active elements with significantly improved photostability, efficiency and operation lifetime, compared to those for the polyurethane acrylate matrix, hardened by a radical photopolymerization method. Changing the liquid (ethanol) medium to polymers causes an increase of fluorescence quantum yield and efficiency. For the first time, covalent bonding between a cyanine dye and a polyurethane has been studied, and high fluorescence quantum yield and generation efficiency have been observed.