Pyrazole‐substituted Near‐infrared Cyanine Dyes Exhibit pH‐dependent Fluorescence Lifetime Properties

Near‐infrared heptamethine cyanine dye is functionalized with pyrazole derivatives at the meso‐position to induce pH‐dependent photophysical properties. The presence of pyrazole unsubstituted at ¹N‐position is essential to induce pH‐dependent fluorescence intensity and lifetime changes in these dyes. Replacement of meso‐chloro group of cyanine dye IR820 with ¹N‐unsubstituted pyrazole resulted in the pH‐dependent fluorescence lifetime changes from 0.93 ns in neutral media to 1.27 ns in acidic media in DMSO. Time‐resolved emission spectra (TRES) revealed that at lower pH, the pyrazole consists of fluorophores with two distinct lifetimes, which cor‐responds to pH‐sensitive and non‐pH‐sensitive species. In contrast, ¹N‐substituted pyrazoles do not exhibit pH response, suggesting excited state electron transfer as the mechanism of pH‐dependent fluorescence lifetime sensitivity for this class of compounds.     

Synthesis and functionalization of dendron‐polymer conjugate based hydrogels via sequential thiol‐ene “click” reactions

Fabrication and functionalization of hydrogels from well‐defined dendron‐polymer‐dendron conjugates is accomplished using sequential radical thiol‐ene “click” reactions. The dendron‐polymer conjugates were synthesized using an azide‐alkyne “click” reaction of alkene‐containing polyester dendrons bearing an alkyne group at their focal point with linear poly(ethylene glycol)‐bisazides. Thiol‐ene “click” reaction was used for crosslinking these alkene functionalized dendron‐polymer conjugates using a tetrathiol‐based crosslinker to provide clear and transparent hydrogels. Hydrogels with residual alkene groups at crosslinking sites were obtained by tuning the alkene‐thiol stoichiometry. The residual alkene groups allow efficient postfunctionalization of these hydrogel matrices with thiol‐containing molecules via a subsequent radical thiol‐ene reaction. The photochemical nature of radical thiol‐ene reaction was exploited to fabricate micropatterned hydrogels. Tunability of functionalization of these hydrogels, by varying dendron generation and polymer chain length was demonstrated by conjugation of a thiol‐containing fluorescent dye. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 926–934     

Novel Cyanine Dyes: Synthesis,Characterization and Photosensitization‐Structure Correlation

Novel furo, thieno and pyrrolo[2,3‐b]pyrazole cyanine dyes were synthesized. The structure‐photosensitization properties correlation of the dyes were examined in 95% ethanol solution by absorption spectroscopy. The chemical structure of the starting biheterocyclic compounds and their derived cyanine dyes were confirmed by elemental analysis, IR and ¹H NMR spectroscopy.     

Thiol‐ene and thiol‐yne‐based synthesis of glycodendrimers as nanomolar inhibitors of wheat germ agglutinin

Alkene and alkyne functional polyester‐based dendrimers of generation 1 to 4 have been prepared and reacted under free‐radical conditions with 2‐acetamido‐2‐deoxy‐1‐thio‐β‐D ‐glucose (GlcNAc‐SH). As the alkene‐dendrimers underwent the addition of one thiyl radical per ene group whereas each yne group of alkyne‐dendrimers was saturated by two thiyl radicals, a collection of glycodendrimers with glycan density ranging from six to ninety‐six GlcNAc per dendrimer was obtained. The recognition properties of the prepared glycodendrimers toward the wheat germ agglutinin (WGA) were evaluated by enzyme‐linked lectin assay (ELLA). The eight glycodendrimers were excellent ligands showing IC₅₀ values in the nanomolar range and relative potencies per sugar unit up to 2.27 e⁶ when compared to monosaccharidic GlcNAc used as monovalent reference. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2422–2433     

Mechanistic Understanding of the Divergent Cyclizations of o‐Alkynylbenzaldehyde Acetals and Thioacetals Catalyzed by Metal Halides

The mechanisms of regiodivergent cyclizations of o‐alkynylbenzaldehyde acetals and thioacetals catalyzed by Pd and Pt halides are studied. DFT calculations found that both reactions are initiated by electrophilic activation of the acetylenic moiety instead of the previously proposed metal‐triggered C?X (X=O, S) cleavage. Both the regioselective cyclization of the π‐alkyne complex and the chemoselective [1,2]‐migration in the carbenoid intermediate were determined as key steps to achieving the observed divergence. For acetal derivatives containing an internal alkyne, the 6‐endo‐dig cyclization is more favorable and leads to the carbenoid intermediate easily through further steps of C?X fragmentation and carbocation cyclization. Then, from the carbenoid intermediate, the [1,2]‐migration of sulfur is easier than that of H, Me, and Ph; whereas, a reversed aptitude was predicted for the oxygen analogue, which is consistent with the greater ability of sulfur atoms to stabilize β‐carbocations. However, for precursors containing a terminal alkyne, the 5‐exo‐dig pathway is preferred and only the 1,2‐disubstituted indene product is seen, irrespective of the nature of the acetal; thus, a different product from that reported in the literature is predicted for benzaldehyde acetal with a terminal alkyne at the ortho position. This prediction led us to reconsider some of the reported results and hidden realities were uncovered with solid new experimental evidence.     

New 1,3,4‐Oxadiazinoisoquinoline Methine Cyanine Dyes: Synthesis,Photosensitivity and Antibacterial Activity

New heterocyclic ring system including 1,3,4‐oxadiazino[6,5‐c]isoquinoline was prepared and employed as a precursor for preparation of monomethine and trimethine cyanine dyes. The structure of the new compounds was characterized via elemental analysis and mass, ¹H‐NMR, and ¹³C‐NMR spectroscopy. The photosensitivity (electronic transitions inside the dye molecule due to photon absorption) of the new methine cyanine dyes was investigated by studying their visible spectra in absolute ethanol and showed its maxima in the visible range of the spectrum with relatively strong absorption bands. The antibacterial activity of the newly synthesized compounds was evaluated against some bacterial strains, resulting in a promising antibacterial efficacy that recommend the tested compounds as new candidates for further pharmaceutical evaluations.     

Protein purification by aminosquarylium cyanine dye‐affinity chromatography

The most selective purification method for proteins and other biomolecules is affinity chromatography. This method is based on the unique biological‐based specificity of the biomolecule–ligand interaction and commonly uses biological ligands. However, these ligands may present some drawbacks, mainly because of their cost and lability. Dye‐affinity chromatography overcomes the limitations of biological ligands and is widely used owing to the low cost of synthetic dyes and to their resistance to biological and chemical degradation. In this work, immobilized aminosquarylium cyanine dyes are used in order to exploit affinity interactions with standard proteins such as lysozyme, α‐chymotrypsin and trypsin. These studies evaluate the affinity interactions occurring between the immobilized ligand and the different proteins, as a reflection of the sum of several molecular interactions, namely ionic, hydrophobic and van der Waals, spread throughout the structure, in a defined spatial manner. The results show the possibility of using an aminosquarylium cyanine dye bearing a N‐hexyl pendant chain, with a ligand density of 1.8 × 10^?2 mmol of dye/g of chromatographic support, to isolate lysozyme, α‐chymotrypsin and trypsin from a mixture. The application of a decreasing ammonium sulfate gradient resulted in the recovery of lysozyme in the flowthrough. On the other hand, α‐chymotrypsin and trypsin were retained, involving different interactions with the ligand. In conclusion, this study demonstrates the potential applicability of ligands such as aminosquarylium cyanine dyes for the separation and purification of proteins by affinity chromatography. Copyright © 2013 John Wiley & Sons, Ltd.     

Rational Molecular Design and Synthesis of Highly Thermo‐ and Photostable Near‐Infrared‐Absorbing Heptamethine Cyanine Dyes with the Use of Fluorine Atoms

Highly thermo‐ and photostable, near‐infrared‐absorbing heptamethine cyanine dyes were achieved with the use of fluorine‐containing components. In particular, one prepared heptamethine cyanine dye, bearing a tetrakis(pentafluorophenyl)borate as a counter anion and an N‐ethyl‐2,2,2‐trifluoroacetamido group at the meso position, showed not only a high decomposition temperature (T_dt), but also very high photostability toward white LED irradiation.     

Studies of 2‐Azaazulenium Derivatives: Unsymmetrical Trimethine Cyanine Dyes Bearing a 2‐Azaazulenium Moiety as One of the Terminal Groups

We report here the synthesis of a series of symmetrical and unsymmetrical trimethine cyanine dyes derived from 2‐azaazulene, combined spectral and quantum‐chemical investigations of their molecular geometry and electron structure, as well as the nature of the lowest electron transitions. Based on the analysis of both calculations and experimental data obtained from absorption and ¹³C NMR spectra, it was concluded that the 2‐azaazulene residue can be treated as a weakly basic terminal group; its donor properties are provided with the participation of the HOMO?1, in contrast to the typical Brooker’s terminal residues with their donor HOMOs. The new classification of the terminal groups of cyanine dyes, and hence the classification of types of unsymmetrical cyanines, is proposed. It is shown that the nature of the higher electron transitions (delocalized or local) in the cyanine dyes depends on their type. In the unsymmetrical trimethine cyanine of the mixed type, negative deviations are observed in their absorption spectra.     

Sterically Shielded Heptamethine Cyanine Dyes for Bioconjugation and High Performance Near‐Infrared Fluorescence Imaging

The near‐infrared window of fluorescent heptamethine cyanine dyes greatly facilitates biological imaging because there is deep penetration of the light and negligible background fluorescence. However, dye instability, aggregation, and poor pharmacokinetics are current drawbacks that limit performance and the scope of possible applications. All these limitations are simultaneously overcome with a new molecular design strategy that produces a charge balanced and sterically shielded fluorochrome. The key design feature is a meso‐aryl group that simultaneously projects two shielding arms directly over each face of a linear heptamethine polyene. Cell and mouse imaging experiments compared a shielded heptamethine cyanine dye (and several peptide and antibody bioconjugates) to benchmark heptamethine dyes and found that the shielded systems possess an unsurpassed combination of photophysical, physiochemical, and biodistribution properties that greatly enhance bioimaging performance.     

Stable,Wavelength‐Tunable Fluorescent Dyes in the NIR‐II Region for In Vivo High‐Contrast Bioimaging and Multiplexed Biosensing

Small‐molecule organic fluorophores, spectrally active in the 900–1700 nm region, with tunable wavelength and sensing properties are sought‐after for in vivo optical imaging and biosensing. A panel of fluorescent dyes ( CX ) has been developed to meet this challenge. CX dyes exhibit the wavelength tunability of cyanine dyes and have a rigidified polymethine chain to guarantee their stability. They are chemo‐ and photo‐stable in an aqueous environment and have tunable optical properties with maximal absorbing/emitting wavelength at 1089/1140 nm. They show great potential in high‐contrast in vivo bioimaging and multicolor detection with negligible optical cross talk. Förster resonance energy transfer (FRET) between CX dyes was demonstrated in deep tissue, providing an approach for monitoring drug‐induced hepatotoxicity by detection of OONO^?. This report presents a series of NIR‐II dyes with promising spectroscopic properties for high‐contrast bioimaging and multiplexed biosensing.     

Stable,Wavelength‐Tunable Fluorescent Dyes in the NIR‐II Region for In Vivo High‐Contrast Bioimaging and Multiplexed Biosensing

Small‐molecule organic fluorophores, spectrally active in the 900–1700 nm region, with tunable wavelength and sensing properties are sought‐after for in vivo optical imaging and biosensing. A panel of fluorescent dyes ( CX ) has been developed to meet this challenge. CX dyes exhibit the wavelength tunability of cyanine dyes and have a rigidified polymethine chain to guarantee their stability. They are chemo‐ and photo‐stable in an aqueous environment and have tunable optical properties with maximal absorbing/emitting wavelength at 1089/1140 nm. They show great potential in high‐contrast in vivo bioimaging and multicolor detection with negligible optical cross talk. Förster resonance energy transfer (FRET) between CX dyes was demonstrated in deep tissue, providing an approach for monitoring drug‐induced hepatotoxicity by detection of OONO^?. This report presents a series of NIR‐II dyes with promising spectroscopic properties for high‐contrast bioimaging and multiplexed biosensing.     

Manganese‐Induced Triplet Blinking and Photobleaching of Single Molecule Cyanine Dyes

Irradiation of solutions of the cyanine dyes Cy3, Cy3B, and Cy5 in the presence of Mn²⁺ causes an increase in the yield of formation of the triplet state of the dye. This results in increased photobleaching and triplet blinking. Experiments with other divalent ions and paramagnetic molecules suggest that the enhancement in the intersystem‐crossing rate is related to the paramagnetic nature of the Mn²⁺ cation. The results are consistent with a model in which the formation of a weak collisional complex between the dye and the ion results in mixing of the singlet and triplet states of the dye. These findings are particularly significant in single‐molecule spectroscopy and super‐resolution imaging methods, in which photobleaching and blinking play an important role.     

Synthesis and Characterization of γ‐Heteroaryl‐substituted Pentamethine Cyanine Dyes with Carboxy or Methoxycarbonyl Substituents at the Two Heterocyclic End Groups

Seven novel pentamethine cyanine dyes with 3,5‐dimethylpyridinium‐1‐yl, pyridinium‐1‐yl, and 1‐quinolinum‐1‐yl substituents in the γ position of the methine chain containing ester or carboxylic acid groups in the ring of the dyes were synthesized via a three‐step procedure. The visible spectral behavior of the pentamethine cyanine dyes was examined in DMSO. Elemental analysis, IR, ¹H‐NMR, ¹³C‐NMR, and mass spectral (MS) data confirmed the molecular structure of the newly synthesized compounds.     

Ethoxy‐substituted Oligo‐phenylenevinylene‐Bridged Organic Dyes for Efficient Dye‐Sensitized Solar Cells

Organic dyes with ethoxy‐substituted oligo‐phenylenevinylene as chromophores were synthesized for dye‐sensitized solar cells (DSSCs), and the detailed relationships between the dye structures, photophysical properties, electrochemical properties, and performances of DSSCs were described. The dye S3O showed broad IPCE spectra in the spectral range of 350–750 nm, and the dye S1P showed solar energy‐to‐electricity conversion efficiency (() of up to 4.23% under AM 1.5 irradiation (100 mW/cm²) in comparison with the reference Ru‐complex (N719 dye) with an η value of 5.90% under similar experimental conditions.     

Structure–Performance Correlations of Organic Dyes with an Electron‐Deficient Diphenylquinoxaline Moiety for Dye‐Sensitized Solar Cells

The high performances of dye‐sensitized solar cells (DSSCs) based on seven new dyes are disclosed. Herein, the synthesis and electrochemical and photophysical properties of a series of intentionally designed dipolar organic dyes and their application in DSSCs are reported. The molecular structures of the seven organic dyes are composed of a triphenylamine group as an electron donor, a cyanoacrylic acid as an electron acceptor, and an electron‐deficient diphenylquinoxaline moiety integrated in the π‐conjugated spacer between the electron donor and acceptor moieties. The DSSCs based on the dye DJ104 gave the best overall cell performance of 8.06 %; the efficiency of the DSSC based on the standard N719 dye under the same experimental conditions was 8.82 %. The spectral coverage of incident photon‐to‐electron conversion efficiencies extends to the onset at the near‐infrared region due to strong internal charge‐transfer transition as well as the effect of electron‐deficient diphenylquinoxaline to lower the energy gap in these organic dyes. A combined tetraphenyl segment as a hydrophobic barrier in these organic dyes effectively slows down the charge recombination from TiO₂ to the electrolyte and boosts the photovoltage, comparable to their Ru^II counterparts. Detailed spectroscopic studies have revealed the dye structure–cell performance correlations, to allow future design of efficient light‐harvesting organic dyes.     

Organic Dyes Containing Pyrenylamine‐Based Cascade Donor Systems with Different Aromatic π Linkers for Dye‐Sensitized Solar Cells: Optical,Electrochemical, and Device Characteristics

New organic dyes containing pyrenylamine donors in a cascade arrangement and cyanoacrylic acid acceptors have been synthesized and characterized by optical, electrochemical, and theoretical studies. The dyes inherit a D ‐π¹‐D ‐π²‐A (D=donor, A=acceptor) molecular architecture where the π linkers π¹ are changed from phenyl to biphenyl and fluorene, whereas the π linker π² that connects the donor fragment with the acceptor is a phenyl unit. The conjugation pathway linking the two donor segments has been found to play a major role in the optical and electrochemical properties. Shorter π linkers such as phenyl groups facilitate the donor–acceptor interaction while the nonplanar biphenyl spacer decreases the electronic communication between the donors and enhances the oxidation propensity of the corresponding dye. All the dyes display an intense longer wavelength electronic transition,which is attributable to the amine‐to‐cyanoacrylic acid charge transfer. The extinction coefficient of this peak grows dramatically on increasing the conjugation pathway length between the two donor segments. The dyes were used as sensitizers in nanocrystalline TiO₂‐based dye‐sensitized solar cells (DSSCs) and the cascade donor system contributed to the enhancement in the device efficiency due to favorable absorption and redox properties.     

Bis(phenothiazyl‐ethynylene)‐Based Organic Dyes Containing Di‐Anchoring Groups with Efficiency Comparable to N719 for Dye‐Sensitized Solar Cells

A new series of acetylene‐bridged phenothiazine‐based di‐anchoring dyes have been synthesized, fully characterized, and used as the photoactive layer for the fabrication of conventional dye‐sensitized solar cells (DSSCs). Tuning of their photophysical and electrochemical properties using different π‐conjugated aromatic rings as the central bridges has been demonstrated. This molecular design strategy successfully inhibits the undesirable charge recombination and prolongs the electron lifetime significantly to improve the power conversion efficiency (η ), which was proven by the detailed studies of electrochemical impedance spectroscopy (EIS) and open‐circuit voltage decay (OCVD). Under a standard air mass (AM) 1.5 irradiation (100 mW cm⁻²), the DSSC based on the dye with phenyl bridging unit exhibits the highest η of 7.44 % with open‐circuit photovoltage (V _oc) of 0.796 V, short‐circuit photocurrent density (J _sc) of 12.49 mA cm⁻² and fill factor (ff) of 0.748. This η value is comparable to that of the benchmark N719 under the same conditions.     

Mechanistic Study of the Rhodium‐Catalyzed [3+2+2] Carbocyclization of Alkenylidenecyclopropanes with Alkynes

A systematic theoretical study has been performed on the recently reported Rh^I‐catalyzed [3+2+2] carbocyclization reactions between alkenylidenecyclopropanes (ACPs) and alkynes. With the aid of theoretical calculations, two possible mechanisms, that is, alkene‐carbometalation‐first and alkyne‐carbometalation‐first mechanisms, are examined in this study. In the oxidative addition step, the possibility of reaction on either the distal or proximal C? C bond of the cyclopropane group has been evaluated. The calculations indicate that the alkene‐activation‐first mechanism is more favored for the overall catalytic cycle. This mechanism involves four steps, that is, oxidative addition of the distal (rather than the proximal) C? C bond of cyclopropane group, alkene carbometalation, alkyne carbometalation, and reductive elimination. The rate‐determining step in the overall catalytic cycle is the carbometalation of the alkyne (i.e., the alkyne‐insertion step) and this step also determines the regioselectivity. Finally, the origin of the regioselectivity is determined by the steric effect (i.e., the steric crowding between the electron‐withdrawing group on alkyne and other ligands on the rhodium center) in the alkyne‐insertion step.     

Ultrafast Photoinduced Electron Transfer in Viologen‐Linked BODIPY Dyes

New boron‐dipyrromethene (BODIPY) dyes linked to viologen are prepared and their photophysical and electrochemical properties are investigated. Both synthesized molecules have similar electronic absorption spectra with the absorption maximum localized at 517 and 501 nm for dye 1 and dye 2 , respectively. They exhibit well‐defined redox behavior, highlighting the presence of BODIPY and viologen subunits, with little perturbation of the redox potential of both subunits with respect to the parent compounds. Both dyes are heavily quenched by photoinduced electron transfer from the BODIPY to the viologen subunit. The transient absorption technique demonstrates that dye 2 forms the viologen radical within a timeframe of 7.1 ps, and that the charge‐separated species has a lifetime of 59 ps. Sustained irradiation of dye 2 in the presence of a tertiary amine allows for the accumulation of BODIPY–methyl‐4,4′‐bipyridinium (BODIPY–MV⁺), as observed by its characteristic absorption at 396 and 603 nm. However, dye 2 does not generate catalytic amounts of hydrogen under standard conditions.