Non-covalent interactions of coumarin dyes with cucurbit[7]uril macrocycle: modulation of ICT to TICT state conversion

Non-covalent interaction of coumarin laser dyes, namely coumarin-1 (C1), coumarin-481 (C481) and coumarin-6H (C6H), with a versatile macrocyclic host molecule cucurbit[7]uril (CB7), has been investigated in aqueous solution using photophysical methods. Steady-state and time-resolved fluorescence studies illustrate significant enhancements/modifications in the fluorescence yields, lifetimes and spectral features of C1, C481 and C6H on interaction with CB7, and are assigned to 1 : 1 complex formation between the dyes and the CB7 host. The complex formation is mainly driven by charge-dipole interaction, as evident from the binding constant values (K ~ 10(4)-10(5) M(-1)). The large changes in the excited state behaviour of C1 and C481 as compared to C6H in the presence of CB7 indicate that CB7 binds C1 and C481 through the encapsulation of the 7-N,N'-diethylamino group of the dyes and the structural rigidity imposed by this interaction dramatically alters the excited state properties of the dyes by preventing the conversion of their emissive intramolecular charge transfer (ICT) state to the non-radiative twisted intramolecular charge transfer (TICT) state. The present results direct towards the probable supramolecular approach using water soluble macrocyclic CB7, in the development of aqueous dye laser systems in the blue-green region.     

First Highly Efficient and Photostable E and C Derivatives of 4,4‐Difluoro‐4‐bora‐3a,4a‐diaza‐s‐indacene (BODIPY) as Dye Lasers in the Liquid Phase,Thin Films,and Solid‐State Rods

A new library of E‐ and C‐4,4‐difluoro‐4‐bora‐3a,4a‐diaza‐s‐indacene (BODIPY) derivatives has been synthesized through a straightforward protocol from commercially available BODIPY complexes, and a systematic study of the photophysical properties and laser behavior related to the electronic properties of the B‐substituent group (alkynyl, cyano, vinyl, aryl, and alkyl) has been carried out. The replacement of fluorine atoms by electron‐withdrawing groups enhances the fluorescence response of the dye, whereas electron‐donor groups diminish the fluorescence efficiency. As a consequence, these compounds exhibit enhanced laser action with respect to their parent dyes, both in liquid solution and in the solid phase, with lasing efficiencies under transversal pumping up to 73 % in liquid solution and 53 % in a solid matrix. The new dyes also showed enhanced photostability. In a solid matrix, the derivative of commercial dye PM597 that incorporated cyano groups at the boron center exhibited a very high lasing stability, with the laser emission remaining at the initial level after 100 000 pump pulses in the same position of the sample at a 10 Hz repetition rate. Distributed feedback laser emission was demonstrated with organic films that incorporated parent dye PM597 and its cyano derivative. The films were deposited onto quartz substrates engraved with appropriate periodical structures. The C derivative exhibited a laser threshold lower than that of the parent dye as well as lasing intensities up to three orders of magnitude higher.     

Uptake of Hydrocarbons in Aqueous Solution by Encapsulation in Acyclic Cucurbit[n]uril‐Type Molecular Containers

The ability of two water‐soluble acyclic cucurbit[n]uril (CB[n]) type containers, whose hydrophobic cavity is defined by a glycoluril tetramer backbone and terminal aromatic (benzene, naphthalene) sidewalls, to act as solubilizing agents for hydrocarbons in water is described. ¹H NMR spectroscopy studies and phase‐solubility diagrams establish that the naphthalene‐walled container performs as well as, or better than, CB[7] and CB[8] in promoting the uptake of poorly soluble hydrocarbons into aqueous solution through formation of host–hydrocarbon complexes. The naphthalene‐walled acyclic CB[n] container is able to extract large hydrocarbons from crude oil into aqueous solution.     

Near‐Infrared Croconaine Rotaxanes and Doped Nanoparticles for Enhanced Aqueous Photothermal Heating

The photothermal effect is the generation of heat by molecules or particles upon high‐energy laser irradiation, and near‐infrared absorbers such as gold nanoparticles and organic dyes have a range of potential photothermal applications. The favourable photothermal properties of thiophene‐functionalised croconaine dyes were recently discovered. The synthesis and properties of novel croconaine rotaxane and pseudorotaxane architectures capable of efficient photothermal performance in both organic and aqueous environments are reported. The versatility of this dye‐encapsulation strategy was demonstrated by the preparation of two organic croconaine rotaxanes using different synthetic methods: the formation of an aqueous pseudorotaxane association complex, and the synthesis of water‐soluble, croconaine‐doped silicated micelle nanoparticles. All of these near‐infrared‐absorbing systems exhibit excellent photothermal behaviour, with pseudorotaxane and rotaxane formation vital for effective aqueous heat generation. Dye encapsulation provides steric protection to enhance the stability of a water‐sensitive croconaine dye, while rotaxane‐doped nanoparticles avoid detrimental band broadening caused by chromophore coupling.     

Modulation of Excited‐State Proton Transfer of 2‐(2′‐Hydroxyphenyl)benzimidazole in a Macrocyclic Cucurbit[7]uril Host Cavity: Dual Emission Behavior and pKa Shift

The effect of the macrocyclic host, cucurbit[7]uril (CB7), on the photophysical properties of the 2‐(2′‐hydroxyphenyl)benzimidazole (HPBI) dye have been investigated in aqueous solution by using ground‐state absorption and steady‐state and time‐resolved fluorescence measurements. All three prototropic forms of the dye (cationic, neutral, and anionic) form inclusion complexes with CB7, with the largest binding constant found for the cationic form (K≈2.4×10⁶ M ^?1). At pH≈4, the appearance of a blue emission band upon excitation of the HPBI cation in the presence of CB7 indicates that encapsulation into the CB7 cavity retards the deprotonation process of the excited cation, and hence reduces its subsequent conversion to the keto form. Excitation of the neutral form (pH≈8.5), however, leads to an increase in the keto form fluorescence, indicating an enhanced excited‐state intramolecular proton‐transfer process for the encapsulated dye. In both the ground and excited states, the two pK_a values of the HPBI dye show upward shifts in the presence of CB7. The prototropic equilibrium of the CB7‐complexed dye is represented by a six‐state model, and the pH‐dependent changes in the binding constants have been analyzed accordingly. It has been observed that the calculated pK_a values using this six‐state model match well with the values obtained experimentally. The changes in the pK_a values in the presence of CB7 have been corroborated with the modulation of the proton‐transfer process of the dye within the host cavity.     

Complexation and Fluorescence of Tricyclic Basic Dyes Encapsulated in Cucurbiturils

Tricyclic basic dyes (proflavine, acridine orange, pyronine, pyronine Y, oxonine, thionine and methylene blue) often form one‐to‐one or two‐to‐one complexes with CB[7] and CB[8], respectively. In the case of pyronine Y, the complexes with CB[7] and CB[8] have a one‐to‐one and three‐to‐one stoichiometry, respectively. The binding constants for CB[7] complexes range from 3.07×10⁶ to 1.70×10⁷ m ^?1. In the case of CB[8], the association constant varies between 3.24×10¹³ and 2.50×10¹⁶ m ^?2. Overall, these binding constants are four orders of magnitude higher than those reported for the same dyes in β and γ‐cyclodextrins. Formation of the host–guest complexes leads to an increase in the fluorescence quantum yields in the case of CB[7], while the dimeric or trimeric dye encapsulated in CB[8] are remarkably less fluorescent than the same dye in diluted solutions.     

Local Extraction and Condensation under a Microscope Using the Optically Controlled Phase Separation of a Thermoresponsive Polymer

In‐situ extraction and condensation of various dyes were carried out in a phase‐separation region of a thermoresponsive polymer aqueous solution generated by near infrared (NIR) laser heating under a microscope. The NIR laser irradiation was directed at a chromium line deposited on a glass substrate, thereby causing local heating of the solution due to the photothermal effect. A phase‐separation region was formed by dehydration of the thermoresponsive polymer followed by ejection of water outside of the phase‐separation region. When various dyes were included in the solution, some dye molecules were extracted into the phase‐separation region, where they condensed. In the case of poly(N‐isopropylacrylamide) (PNIPAM, 10 wt % in an aqueous solution) as the thermoresponsive polymer and crystal violet (CV) as the dye (0.1 mM ), CV condensed by about 25 times. It was found that one of the necessary conditions for the extraction/condensation is the hydrophobicity of the dye molecule; however, the dominant cause for accumulating inside the PNIPAM chain is the molecular interaction between the amide group in the side chain of PNIPAM and the functional groups such as carbonyl or amino groups in the dye molecules.     

Effect of cucurbit[8]uril on the spectral and luminescent properties of alkyl-substituted thiacarbocyanines

In the presence of cucurbit[8]uril, polymethine dyes 3,3’-dimethylthiacarbocyanine (DMCy) and 3,3’-diethylthiacarbocyanine (DECy) in aqueous solution can form both nonfluorescing D@CB8 and fluorescing D@2CB8 dimer complexes. The D@2CB8 complexes with DMCy have a symmetrical narrow absorption band. The substitution of the СН₃ group in DMCy for the С₂Н₅ group in the DECy molecule results in a difference in the absorption spectra of the dimeric dye complexes. Quantum chemical calculations show a difference in structure between the dimeric complexes for DMCy and DECy. The enthalpies of dimerization of DMCy and DECy in water and of the formation of complexes D@CB8 and D@2CB8 are close.     

Click assembly of dye-functionalized octasilsesquioxanes for highly efficient and photostable photonic systems

New hybrid organic–inorganic dyes based on an azide‐functionalized cubic octasilsesquioxane (POSS) as the inorganic part and a 4,4‐difluoro‐4‐bora‐3a,4a‐diaza‐s‐indacene (BDP) chromophore as the organic component have been synthesized by copper(I)‐catalyzed 1,3‐dipolar cycloaddition of azides to alkynes. We have studied the effects of the linkage group of BDP to the POSS unit and the degree of functionalization of this inorganic core on the ensuing optical properties by comparison with model dyes. The high fluorescence of the BDP dye is preserved in spite of the linked chain at its meso position, even after attaching one BDP moiety to the POSS core. The laser action of the new dyes has been analyzed under transversal pumping at 532 nm in both the liquid phase and when incorporated into solid polymeric matrices. The monosubstituted new hybrid dye exhibits high lasing efficiency of up to 56 % with high photostability, with its laser output remaining at the initial value after 4×10⁵ pump pulses in the same position of the sample at a repetition rate of 30 Hz. However, functionalization of the POSS core with eight fluorophores leads to dye aggregation, as quantum mechanical simulation has revealed, worsening the optical properties and extinguishing the laser action. The new hybrid systems based on dye‐linked POSS nanoparticles open up the possibility of using these new photonic materials as alternative sources for optoelectronic devices, competing with dendronized or grafted polymers.     

A Computational and Experimental Study of Thieno[3,4‐b]thiophene as a Proaromatic π‐Bridge in Dye‐Sensitized Solar Cells

Four D ‐π‐A dyes (D=donor, A=accpetor) based on a 3,4‐thienothiophene π‐bridge were synthesized for use in dye‐sensitized solar cells (DSCs). The proaromatic building block 3,4‐thienothiophene is incorporated to stabilize dye excited‐state oxidation potentials. This lowering of the excited‐state energy levels allows for deeper absorption into the NIR region with relatively low molecular weight dyes. The influence of proaromatic functionality is probed through a computational analysis of optimized bond lengths and nucleus independent chemical shifts (NICS) for both the ground‐ and excited‐ states. To avoid a necessary lowering of the TiO₂ semiconductor conduction band (CB) to promote efficient dye–TiO₂ electron injection, strong donor functionalities based on triaryl‐ and diarylamines are employed in the dye designs to raise both the ground‐ and excited‐state oxidation potentials of the dyes. Solubility, aggregation, and TiO₂ surface protection are addressed by examining an ethylhexyl alkyl chain in comparison to a simple ethyl chain on the 3,4‐thienothiophene bridge. Power conversion efficiencies of up to 7.8 % are observed.     

High‐Performance Organic Materials for Dye‐Sensitized Solar Cells: Triarylene‐Linked Dyads with a 4‐tert‐Butylphenylamine Donor

A series of organic dyes were prepared that displayed remarkable solar‐to‐energy conversion efficiencies in dye‐sensitized solar cells (DSSCs). These dyes are composed of a 4‐tert‐butylphenylamine donor group (D), a cyanoacrylic‐acid acceptor group (A), and a phenylene‐thiophene‐phenylene (PSP) spacer group, forming a D‐π‐A system. A dye containing a bulky tert‐butylphenylene‐substituted carbazole (CB) donor group showed the highest performance, with an overall conversion efficiency of 6.70 %. The performance of the device was correlated to the structural features of the donor groups; that is, the presence of a tert‐butyl group can not only enhance the electron‐donating ability of the donor, but can also suppress intermolecular aggregation. A typical device made with the CB‐PSP dye afforded a maximum photon‐to‐current conversion efficiency (IPCE) of 80 % in the region 400–480 nm, a short‐circuit photocurrent density J_sc=14.63 mA cm^?2, an open‐circuit photovoltage V_oc=0.685 V, and a fill factor FF=0.67. When chenodeoxycholic acid (CDCA) was used as a co‐absorbent, the open‐circuit voltage of CB‐PSP was elevated significantly, yet the overall performance decreased by 16–18 %. This result indicated that the presence of 4‐tert‐butylphenyl substituents can effectively inhibit self‐aggregation, even without CDCA.     

Solid‐state lasers based on inorganic–organic hybrid materials obtained by combined sol–gel polymer technology

Sol–gel glass matrices in which organic laser dyes are embedded can be used as the gain medium in solid‐state, continuously tunable lasers. Such lasers are very simple to construct, and potentially very compact and efficient. Unlike the commonly used liquid dye laser systems, solid‐state dye lasers can be made mechanically robust and portable. In this article, the development of sol–gel/dye lasers, including the sol–gel technology, dye properties, and laser operation, is reviewed. In addition, new solid‐state hosts (such as polyurethane/silica ORMOSILs), additional organic dyes (cyanines), and new studies on the stability of the dyes are presented. Copyright © 2004 John Wiley & Sons, Ltd.     

A Supramolecularly Activated Radical Cation for Accelerated Catalytic Oxidation

Tuning the activity of radicals is crucial for radical reactions and radical‐based materials. Herein, we report a supramolecular strategy to accelerate the Fenton reaction through the construction of supramolecularly activated radical cations. As a proof of the concept, cucurbit[7]uril (CB[7]) was introduced, through host–guest interactions, onto each side of a derivative of 1,4‐diketopyrrolo[3,4‐c]pyrrole (DPP), a model dye for Fenton oxidation. The DPP radical cation, the key intermediate in the oxidation process, was activated by the electrostatically negative carbonyl groups of CB[7]. The activation induced a drastic decrease in the apparent activation energy and greatly increased the reaction rate. This facile supramolecular strategy is a promising method for promoting radical reactions. It may also open up a new route for the catalytic oxidation of organic pollutants for water purification and widen the realm of supramolecular catalysis.     

Charge‐selective separation and recovery of organic ions by polymeric micelles

Charge‐selective separation and recovery of organic ionic dyes by polymeric micelles (PMs) are reported. Branched polyethylenimine (PEI) functionalized with 4‐cetyloxybenzaldehyde (CBA) via Schiff‐base bonds (PEI@CBA) can extract an anionic dye from cationic contaminants, and transfer it from an aqueous phase into an apolar oil phase, and thus leading to separation. While a physical micelle of PAA@PS, with polyacrylic acid (PAA) as core and polystyrene (PS) as shell, can selectively extract a cationic dye from anionic contaminants. When polar, yet nonionic groups are eliminated from the core of a PM, charge selectivity can be significantly enhanced. Although many anionic–cationic dyes can form a poorly water‐soluble complex or precipitate, separation is still feasible with a reasonably designed PM. Finally, entrapment of a guest by a PM is found easy but release may be difficult; in this case, PEI@CBA with an acid‐sheddable shell, can recover the entrapped guest. It is also found the encapsulation of a dye is usually accompanied with dye stacking, resulting in a changed UV/vis spectrum. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 872–881     

Investigation on Spectroscopic and Laser Properties of Pyrromethene and Perylene Chromophores in Elastic Polymeric Hosts

In this work, two types of chromophore i.e. the pyrromethene and perylene families dyes were doped into elastic polymeric host materials based on polydimethylsiloxane (PDMS), which had been widely employed in various applications. The solubilities, spectroscopic and laser properties of these dyes doped into PDMS matrices were systematically investigated. Tunable laser output with high conversion efficiencies and low laser thresholds were observed and calculated. The laser longevity of pyrromethene dyes doped in PDMS matrices could exceed 1 × 10⁵ pulses through a fast self‐recovery on the laser output with the elapse of aging time. The efficient and stable laser output of the dopants and the flexibility of the PDMS host provided the feasibility of such gain media as mechanically tunable laser sources, which might be employed as cost‐effective components on integrated bio‐chips.     

Dye removal by a novel hydrogel‐clay nanocomposite with enhanced swelling properties

Acrylamide (AAm)‐2‐acrylamide‐2‐methylpropanesulfonic acid sodium salt (AMPSNa) hydrogel and AAm‐AMPSNa/clay hydrogel nanocomposite having 10 w% clay was prepared by in situ copolymerization in aqueous solution in the presence of a crosslinking agent (N,N′‐methylenebisacrylamide (NMBA)). Swelling properties and kinetics of the hydrogel samples were investigated in water and aqueous solutions of the Safranine‐T (ST) and Brilliant Cresyl Blue (BCB) dyes. The swelling and diffusion parameters were also calculated in water and dye solutions. It was observed that the AAm‐AMPSNa/clay hydrogel nanocomposite exhibits improved swelling capacity compared with the AAm‐AMPSNa hydrogel. It was also found that the diffusion mechanisms show non‐Fickian character. Adsorption properties of the hydrogel samples in the aqueous solution of ST and BCB dyes were also investigated. Clay incorporation into the hydrogel structure increased not only the adsorption capacity but also the adsorption rate. Adsorption capacity values of the hydrogel nanocomposite were found to be 484.2 and 494.2 mg g^?1 for the ST and BCB dyes, respectively. It was seen that the adsorption of dyes by the hydrogel nanocomposite completed in 10 min while the AAm‐AMPSNa hydrogel adsorbed dyes approximately in 90 min. Adsorption data of the samples were modelled by the pseudo‐first‐order and pseudo‐second‐order kinetic equations in order to investigate dye adsorption mechanism. It was found that the adsorption kinetics of hydrogel nanocomposite followed a pseudo‐second‐order model. Equilibrium isotherms were analyzed using the Langmuir and Freundlich isotherms. It was seen that the Langmuir model fits the adsorption data better than the Freundlich model. Copyright © 2008 John Wiley & Sons, Ltd.     

Cucurbituril Encapsulation of Fluorescent Dyes

The potential of cucurbiturils, water-soluble macrocyclic host molecules composed of glycoluril units, for tuning the properties of fluorescent dyes and advancing new applications is illustrated. Cucurbit[7]uril (CB7), which presents a particularly attractive derivative due to its intermediary size and high water solubility, has been shown to display a variety of advantageous effects on fluorescent dyes, which include increased fluorescence intensity and brightness, enhanced photostability, protection towards fluorescence quenchers, solubilization, and deaggregation. Particularly noteworthy is the prolongation of the fluorescence lifetimes of different dyes, which can be traced back to the low polarizability of the host cavity. In addition, the host serves as cation receptor, which causes a considerable shift of protonation equilibria and assists the protonation of fluorescent dyes. The latter effect can be exploited in the design of protolytic fluorophore displacement assays. The perspective of cucurbiturils as stabilizers for laser dyes, enhancement agents in time-resolved fluorescence (TRF) assays, contrast agents for fluorescence lifetime imaging (FLIM), and dyes for fluorescent collectors for solar cells is mentioned. Original experimental results for the effect of CB7 on the fluorescence properties of three dyes (Macrolex Yellow 10 GN, Dapoxyl, and 4-(dimethylamino)benzonitrile) are presented.     

Encapsulation-Controlled Photoisomerization of a Styryl Derivative: Stereoselective Formation of the Anti Z-Isomer in the Cucurbit[7]uril Cavity

The photochemical isomerization of a styrylpyridinium dye ( SP ) bearing an unsymmetrically attached benzo-15-crown-5 ether has been studied in aqueous solution in the absence and presence of cucurbit[7]uril (CB[7]). The detailed analysis of the UV/Vis and NMR spectra showes that the isomeric composition of the photostationary mixtures of SP can be modulated by the host-guest complexation with CB[7]. It was found that steric hindrance caused by encapsulation of SP in the host cavity induces the exclusive formation of the anti conformer of Z- SP in contrast with the mixture of both anti and syn conformers obtained during photoisomerization of the dye without CB[7]. Remarkably, the displacement of anti Z- SP from CB[7] does not lead to the transformation of the anti Z-isomer into the syn Z-isomer pointing out the conformational memory of the system. The results provide an interesting example of the supramolecular stereorecognition by the achiral CB[7] host.     

Host-guest complexation of neutral red with macrocyclic host molecules: contrasting pK(a) shifts and binding affinities for cucurbit[7]uril and beta-cyclodextrin

The photophysical properties of the phenazine-based dye neutral red were investigated in aqueous solution in the presence of the macrocyclic host molecule cucurbit[7]uril (CB7) using ground-state absorption as well as steady-state and time-resolved fluorescence measurements. The results are contrasted to those previously obtained for beta-cyclodextrin (beta-CD; Singh et al. J. Phys. Chem. A 2004, 108, 1465). Both the neutral (NR) and cationic (NRH+) forms of the dye formed inclusion complexes with CB7, with the larger binding constant for the latter (K = 6.5 x 10(3) M(-1) versus 6.0 x 10(5) M(-1)). This result differed from that for beta-CD, where only the neutral form of the dye was reported to undergo sizable inclusion complex formation. From the difference in binding constants and the pK(a) value of protonated neutral red in the absence of CB7 (6.8), an increased pK(a) value of the dye when complexed by CB7 was projected (approximately 8.8). This shift differed again from the behavior of the dye with beta-CD, where a decreased pK(a) value (ca. 6.1) was reported. The photophysical properties of both NR and NRH+ forms showed significant changes in the presence of CB7. Fluorescence anisotropy studies indicated that the inclusion complexes of both forms of the dye rotate as a whole, giving rotational relaxation times much larger than that expected for the free dye in aqueous solution. The thermodynamic parameters for the NRH+.CB7 complex were investigated in temperature-dependent binding studies, suggesting an entropic driving force for complexation related to desolvation of the cation and the removal of high-energy water molecules from the CB7 cavity.     

Red‐Emitting Rhodamines with Hydroxylated,Sulfonated, and Phosphorylated Dye Residues and Their Use in Fluorescence Nanoscopy

Fluorescent dyes emitting red light are frequently used in conventional and super‐resolution microscopy of biological samples, although the variety of the useful dyes is limited. We describe the synthesis of rhodamine‐based fluorescent dyes with absorption and emission maxima in the range of 621–637 and 644–660 nm, respectively and demonstrate their high performance in confocal and stimulated emission depletion (STED) microscopy. New dyes were prepared by means of reliable chemical transformations applied to a rhodamine scaffold with three variable positions. They feature polarity, water solubility, variable net charges, improved stabilities of N‐hydroxysuccinimidyl (NHS) esters, as well as large fluorescence quantum yields in dye solutions and antibody conjugates. The photophysical and imaging properties of dyes containing three different polar groups, namely primary phosphate, sulfonic acid (in two different positions), and hydroxyl were compared. A dye with two primary phosphate groups was explored as a valuable alternative to dyes with “classical” sulfonic acid groups. Due to the increased net charge of the phosphorylated dye (q=?4 at pH 8), it demonstrated a far better electrophoretic mobility compared with analogues with two sulfonic acid groups (q=?2). As an example, one fluorescent dye was designed to be especially convenient for practical use. It is characterized by sufficiently high chemical stability of the NHS ester, its simple isolation, handling, and solubility in aqueous buffers, as well as in organic solvents. All these features, accompanied by a zero net charge in conjugates, were accomplished by the introduction of hydrophilic groups of two types: two hydroxyl groups and one sulfonic acid residue.