Dye Dimers Research Articles

Color‐Change Photoswitching of an Alkynylpyrene Excimer Dye

AbstractWe describe a photoswitchable DNA‐based dimeric dye that visibly changes fluorescence from green to blue upon UV irradiation. A novel bis‐alkyne‐dependent [2+2+2] cycloaddition is proposed as a mechanism for the color change in air. The photoinduced structural switching results in spatial separation of stacked pyrene units, thereby causing selective loss of the excimer emission. We demonstrate and suggest several applications for this novel photoswitch.

Color-Change Photoswitching of an Alkynylpyrene Excimer Dye.

We describe a photoswitchable DNA-based dimeric dye that visibly changes fluorescence from green to blue upon UV irradiation. A novel bis-alkyne-dependent [2+2+2] cycloaddition is proposed as a mechanism for the color change in air. The photoinduced structural switching results in spatial separation of stacked pyrene units, thereby causing selective loss of the excimer emission. We demonstrate and suggest several applications for this novel photoswitch.

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.

Formation of trans-2-[4-(Dimethylamino)Styryl]-3-Ethyl-1,3-Benzothiazolium Perchlorate Dimers in the Presence of Sodium Polystyrene Sulfonate

The spectral properties of a novel thioflavin T derivative, trans-2-[4-(dimethylamino)styryl]-3-ethyl-1,3-benzothiazolium perchlorate (DMASEBT), were studied in aqueous solutions in the presence of sodium polystyrene sulfonate (SPS). It was shown that SPS either could interact with dye monomers or initiate the formation of non-fluorescent dye dimers depending on the concentration ratio of dye and polyelectrolyte. DMASEBT dimer formation in the presence of SPS produced a hypsochromic shift by 40 nm in the absorption spectrum and quenched fluorescence. A bathochromic shift of the absorption spectrum and an increase of the fluorescence intensity by an order of magnitude were observed if DMASEBT monomers interacted with SPS. Quantum-chemical analysis found that sandwich dimers (H-aggregates) were most stable. A comparison of DMASEBT spectra in the presence of SPS and amyloid fibrils showed that DMASEBT molecules were incorporated into amyloid fibrils as monomers. The spectral changes associated with this incorporation could not be explained by the formation of dye aggregates.

Polymeric Self-Assemblies with Boron-Containing Near-Infrared Dye Dimers for Photoacoustic Imaging Probes.

Polymers containing pyrrolopyrrole aza-BODIPY (PPAB) and thiophene-bridged BODIPY dimers (TBD) having poly(ethylene glycol) (PEG) or PEGylated hyaluronic acid (HA) were prepared by facile conjugation approaches. Self-assemblies consisting of TBD-conjugated polymers more efficiently generated photoacoustic (PA) signals than PPAB-PEG conjugate upon irradiation with near-infrared pulsed laser light. Among dye-conjugated polymers examined, TBD-HA-PEG conjugates efficiently generated photoacoustic signals, 1.49-1.83 times stronger than that of commercially available indocyanine green (ICG). We found that the following two factors are essential to enhance PA signals from self-assemblies: (1) the formation of strongly interacting TBD aggregates and (2) enhancement of the elastic modulus of self-assemblies by conjugating TBDs with HA. TBD-conjugated HA derivatives circulated in blood vessels for a longer time (15.6 ± 4.9% injected dose (ID) in blood 24 h after injection) and more specifically accumulated in tumor tissues (17.8 ± 3.5% ID/g in tumor 24 h after injection) than ICG-conjugated HA derivatives, visualizing a tumor site more clearly. The cell uptake experiment of dye-HA conjugates indicates that ICG-conjugated polymers internalized into cells or merged with cell walls to emit strong fluorescence, while TBD-conjugated polymers were not internalized into cells. Because the disassembly of the TBD-conjugated HA derivatives is suppressed, aggregated TBDs emit weak fluorescence but efficiently generate strong PA signals in tumor tissues.

Neutral Aminyl Radicals Derived from Azoimidazolium Dyes.

The synthesis and characterization of a new class of neutral aminyl radicals is reported. Monoradicals were obtained by reduction of azoimidazolium dyes with potassium. Structural, spectroscopic, and computational data suggest that the spin density is centered on one of the nitrogen atoms of the former azo group. The reduction of a dimeric dye with an octamethylbiphenylene bridge between the azo groups resulted in the formation of a biradical with largely independent unpaired electrons. Both the monoradicals and the biradical were found to display high stability in solution as well as in the solid state.

Nature of phosphorescence kinetics of xanthene dyes in biological media

In the paper the experimental results on the nature of the phosphorescence of xanthene dyes in biological media are discussed. Phosphorescence is a monomolecular process and should have exponential type. However, the kinetics of the phosphorescence of xanthene dyes has two-exponential type in biological media. Analysis of data by experimental and theoretical methods showed that the second exponent connects on the phosphorescence of dye dimers. It can be used in biomedical investigation for dose selection of preparation delivery.

Small molecule probes finely differentiate between various ds- and ss-DNA and RNA by fluorescence, CD and NMR response

Two small molecules showed intriguing properties of analytical multipurpose probes, whereby one chromophore gives different signal for many different DNA/RNA by application of several highly sensitive spectroscopic methods. Dyes revealed pronounced fluorescence ratiomeric differentiation between ds-AU-RNA, AT-DNA and GC-DNA in approximate order 10:8:1. Particularly interesting, dyes showed specific fluorimetric response for poly rA even at 10-fold excess of any other ss-RNA, and moreover such emission selectivity is preserved in multicomponent ss-RNA mixtures. The dyes also showed specific chiral recognition of poly rU in respect to the other ss-RNA by induced CD (ICD) pattern in visible range (400–500 nm), which was attributed to the dye-side-chain contribution to binding (confirmed by absence of any ICD band for reference compound lacking side-chain). Most intriguingly, minor difference in the side-chain attached to dye chromophore resulted in opposite sign of dye-ICD pattern, whereby differences in NMR NOESY contacts and proton chemical shifts between two dye/oligo rU complexes combined with MD simulations and CD calculations attributed observed bisignate ICD to the dimeric dye aggregate within oligo rU.

Bichromatic coherent random lasing from dye-doped polymer stabilized blue phase liquid crystals controlled by pump light polarization**Project supported by the National Natural Science Foundation of China (Grant Nos. 11474021 and 51333001), the Key Program for International S&T Cooperation Projects of China (Grant No. 2013DFB50340), the Issues of Priority Development Areas of the Research Fund for the Doctoral Program of Higher

In this paper, we investigate the bichromatic coherent random lasing actions from the dye-doped polymer stabilized blue phase liquid crystals. Two groups of lasing peaks, of which the full widith at half maximum is about 0.3 nm, are clearly observed. The shorter- and longer-wavelength modes are associated with the excitation of the single laser dye (DCM) monomers and dimers respectively. The experimental results show that the competition between the two groups of the lasing peaks can be controlled by varying the polarization of the pump light. When the polarization of the pump light is rotated from 0° to 90°, the intensity of the shorter-wavelength lasing peak group reduces while the intensity of the longer-wavelength lasing peak group increases. In addition, a red shift of the longer-wavelength modes is also observed and the physical mechanisms behind the red-shift phenomenon are discussed.

Novel synthetic approach to near-infrared heptamethine cyanine dyes and spectroscopic characterization in presence of biological molecules

Abstract Two near-infrared symmetric heptamethine cyanine dyes, containing integrated chlorosubstituted cyclohexenyl ring were obtained via a novel synthetic approach, using mild conditions at room temperature. UV–vis and fluorescence properties of the dyes were evaluated in organic solutions varying solvent polarity. Further spectral studies illustrating their application as potential labels for biological molecules, were reported in the presence of deoxyribonucleic acid (DNA), bovine serum albumin (BSA), and phospholipids (PC). The dyes undergo H-type intramolecular complexation between the two cyanine subunits when free in buffer. Absorption studies show that binding of cyanines to DNA, BSA and lipid membranes leads to the red shift in the H-aggregates peak with appearance of monomeric and dimeric dye species pointing to the disaggregation of the dyes under study in the presence of biological molecules. The fact that the decrease of liposome-induced cyanine aggregation was more pronounced in the zwitterionic phosphatidylcholine bilayer, suggests that the disruption of highly organized molecular arrangements are most likely electrostatically-controlled.

Influence of a polarizable surrounding on the electronically excited states of aggregated perylene materials.

To tune the efficiency of organic semiconductor devices it is important to understand limiting factors as trapping mechanisms for excitons or charges. An understanding of such mechanisms deserves an accurate description of the involved electronical states in the given environment. In this study, we investigate how a polarizable surrounding influences the relative positions of electronically excited states of dimers of different perylene dyes. Polarization effects are particularly interesting for these systems, because gas phase computations predict that the CT states lie slightly above the corresponding Frenkel states. A polarizable environment may change this energy order because CT states are thought to be more sensitive to a polarizable surrounding than Frenkel states. A first insight we got via a TD-HF approach in combination with a polarizable continuum model (PCM). These give limited insights because TD-HF overestimates excitation energies of CT states. However, SCS-CC2 approaches, which are sufficiently accurate, cannot easily be used in combination with continuum solvent models. Hence, we developed two approaches to combine gas phase SCS-CC2 results with solvent effects based on TD-HF computations. Their accuracies were finally checked via ADC(2)//COSMO computations. The results show that for perylene dyes a polarizable surrounding alone does not influence the energetic ordering of CT and Frenkel states. Variations in the energy order of the states only result from nuclear relaxation effects after the excitation process. © 2016 Wiley Periodicals, Inc.

Paper No P10: Influence of Dye Molecular Structure on Liquid Crystal Anchoring Energy

AbstractTheoretical description of the photoalignment process details is an urgent task to make the LC alignment more perfect and develop displays with new functions. In this paper we describe formation of photoaligning dye dimers and influence of their molecular structure on both polar Wθ and azimuthal Wφ anchoring energy.

Fluorescent dyes with directly connected xanthone and xanthene units.

Unexpected dimerization of a methoxymethyl-protected xanthone occurred upon treatment with an aryl lithium reagent generated from 2-bromo-1,3-dimethylbenzene and n-butyllithium. The hydrogen between two directing ethereal oxygen atoms was not abstracted, but that adjacent to the carbonyl group was removed to afford a dimeric compound containing two directly connected fluorescent xanthone and xanthene units. Starting from this discovery, three dimeric dyes were constructed, and their optical properties were examined. Although the two fluorescent units were orthogonal in each dye, efficient energy transfer was observed in dimeric dye 16 in three solvent systems. In contrast, solvent-dependent energy transfer was detected for another dimeric dye, 5. After close investigation, we found that the orientation factor (κ) is the main factor influencing Förster resonance energy transfer in these dyes.

Recognizing parallel-stranded G-quadruplex by cyanine dye dimer based on dual-site binding mode

G-quadruplexes (G4s) play important roles in biological systems, such as telomere maintenance, replication, and transcription. Based on the DNA sequence, loop geometry, and the local environments, G4s can be classified into different conformations. It is important to detect different types of G4s to monitor the diseases related with G4s. Most ligands bind to G4s based on end-stacking modes, while rare ligands bind to G4s through groove binding modes. We have found that a cyanine dye DMSB interacts with parallel G4 by end-stacking and groove simultaneous binding mode. In this article, we found that DMSB could simply discriminate parallel G4s from other DNA motifs by using UV-vis spectrum. These results give some clues to develop high specificity G4 probes. (C) 2015 Chinese Chemical Society and Institute of Materia Medica, Chinese Academy of Medical Sciences. Published by Elsevier B.V. All rights reserved.

Theoretical Studies of Electronic Structure and Photophysical Properties of a Series of Indoline Dyes with Triphenylamine Ligand

To design efficient organic sensitizer, a series of D‐π‐A indoline dyes with different donor parts have been investigated by density functional theory (DFT) and time‐dependent DFT (TD‐DFT) approach. The molecular geometries, frontier molecular orbitals, and absorption spectra of these dyes have been systematically investigated to provide comprehensive understanding of the structure‐property relationships. Compared with D149, our designed dyes have proper HOMO and LUMO energy level, narrowed HOMO‐LUMO energy gap, and broadened absorption band by introducing the N(CH3)2 and N(phenyl)2 groups at the donor part. Furthermore, the dimeric dyes and dye‐(TiO2)6 systems have been optimized by DFT method to simulate the intermolecular interactions, as well as interaction between the dyes dimmers and semiconductor interface, respectively. Through the analyses of absorption energies (Eads), energy levels of the HOMO and LUMO, light harvesting efficiency (LHE), and the driving force of electrons injections (ΔGinject), it is found that the designed dyes should have improved optical properties by importing the N(CH3)2 group. This work is hoped to provide a theoretical guiding role in design of new dyes for dye‐sensitized solar cells.

Cucurbit[8]uril-templated H and J dimers of bichromophoric coumarin dyes: origin of contrasting emission.

We report the supramolecular control and mechanism for the contrasting dimer emission from selected bichromophoric coumarin dyes caught in the cucurbit[8]uril cavity-a facile approach to developing photo-responsive molecular assemblies through structural tuning.

Quantum Nonlinear Optics with Polar J-Aggregates in Microcavities.

We predict that an ensemble of organic dye molecules with permanent electric dipole moments embedded in a microcavity can lead to strong optical nonlinearities at the single-photon level. The strong long-range electrostatic interaction between chromophores due to their permanent dipoles introduces the desired nonlinearity of the light-matter coupling in the microcavity. We develop a semiclassical model to obtain the absorption spectra of a weak probe field under the influence of strong exciton-photon coupling with the cavity field. Using realistic parameters, we demonstrate that a cavity field with an average photon number near unity can significantly modify the absorptive and dispersive response of the medium to a weak probe field at a different frequency. Finally, we show that the system is in the regime of cavity-induced transparency with a broad transparency window for dye dimers. We illustrate our findings using pseudoisocyanine chloride (PIC) J-aggregates in currently available optical microcavities.

Light-induced self-assembly and decay of J aggregates of thiamonomethinecyanine dyes.

Formation of J aggregates, that is, one-dimensional supramolecular self-organizations in which the transition moments of individual molecules are aligned parallel to the line joining their centers through a "head-to-tail" arrangement, normally proceed via electrostatic interactions between oppositely charged molecular groups; this is facilitated by an electrolyte medium. Here, we show that J aggregates of thiamonomethinecyanine dyes in a solution can be assembled from dye dimers by illuminating the solution with light of the appropriate wavelength to induce excitation of the dye dimers. The reverse process is also demonstrated by application of light of the correct wavelength to induce excitation of the J aggregates. Our results indicate that spontaneous J aggregation in the dark and formation of J aggregates through illumination proceed through different mechanisms; the former resulting in an increase in the number of the aggregates and the latter in an increase in the size of the aggregates.

Aliphatic/aromatic spacers based azo dye dimers: synthesis and application for optical storage devices

The photoisomerization effect of new bent-shaped azo dyes in the presence of aliphatic and aromatic spacers is reported for the first time. The synthesized compounds with n-hexane and benzene as central moieties were characterized by different spectral analytical techniques such as 1H-NMR, 13C-NMR, FTIR and UV-Vis. They revealed the photoisomerization effect in solution and on the solid cells as well. In solution, the E–Z and Z–E isomerization occurred in around 17–18 seconds and 7–13 hours, respectively. The dramatic variation in back relaxation is speculated to take place due to the nature of the spacers involved in the system. The synthesized materials are expected to be more useful in optical storage devices.

Coupled π-conjugated chromophores: Squaraine dye dimers as two connected pendulums

Intense absorption ability in the near infrared (NIR) region is mandatory for many technologies and applications. The design thereof is however quite complex since only a few dye classes show these properties. Polymeric squaraine dyes have them however they are mostly hardly soluble. Herein four dimeric soluble and easy to prepare squaraine dye dimers are reported with absorption maxima between 679 and 805 nm. The synthesis, characterisation, the determination of the physicochemical properties and the in silico study of the calculated molecular geometry, the molecular orbitals, and the calculated total charge density surface were compared. The coupling of the two chromophores is concluded as a matter of the distance in-between, the π-electron system of the bridge, the spatial orientation thereof, and the spatial orientation of the electronic transition moment. The closer the two chromophores were and the less out-of-plane elements the bridge has, the smaller the optical band gap is.