Types Of J-aggregates Research Articles

Self-Assembly of a Zinc Bacteriochlorophyll-d Analog with a Lipophilic Tertiary Amide Group in the 17-Substituent

Abstract Self-assembled aggregates of bacteriochlorophyll(BChl)-c/d/e pigments play key roles in major light-harvesting antenna systems of photosynthetic green bacteria. Herein, we report the self-assembly of a lipophilic zinc BChl-d model with an N,N-didodecylamide in the 17-substituent. The present model formed two types of J-aggregates, which formed under kinetic and thermodynamic controls.

Unusual enhancement of dye luminescence by exciton resonance of J-Aggregates

In this study, we report an effective excitation energy transfer from J-aggregates to exciton traps (specially selected dye molecules) located within different polymer layers by Förster resonance energy transfer mechanism. With an increase in the distance d between the layer of J-aggregates and that of the exciton traps, the intensity of the traps luminescence reaches a maximum at the certain spacer layer thickness, instead of a gradual decrease according to the Förster law ~ d−6, and then drops down. Moreover, the decay time of the traps luminescence synchronously changes, reaching its maximum at the maximum of the traps luminescence. The observed effect takes place for different types of J-aggregates and exciton traps and even at the direct excitation into the traps absorption band. Despite that, the critical distance between J-aggregates and exciton traps, at which the maximum of the traps luminescence and its highest decay time are observed, was nearly the same for all J-aggregates – exciton traps pairs.

Self-Assembly for Two Types of J-Aggregates: cis-Isomers of Dye on the Carbon Nanotube Surface and Free Aggregates of Dye trans-Isomers

Development of novel nanoscale devices requires unique functional nanomaterials. Furthermore, chemical design of different nanoparticles in one unit is a complex task, particularly the application ...

Formation of J-Aggregates of an Anionic Oxacarbocyanine Dye Upon Interaction with Proteins and Polyelectrolytes

J-aggregation of the anionic oxacarbocyanine dye 3,3′-di-(γ-sulfopropyl)-5,5′-diphenyl-9-ethyloxacarbocyanine betaine was studied in aqueous solutions in the presence of proteins (collagens, immunoglobulin G, serum albumins) and polyelectrolytes (polyethyleneimine, polyvinylpyrrolidone). It was found that denaturation of human serum albumin by urea stimulated J-aggregation of the dye. The dye formed two types of J-aggregates in the presence of denatured albumin and polyethyleneimine. J-aggregates formed in the presence of polyethyleneimine rearranged over time.

Supramolecular Structure of TTBC J-Aggregates in Solution and on Surface

The aggregation behavior of cationic 5,5',6,6'-tetrachloro-1,1',3,3'-tetraethylbenzimidacarbocyanine with chloride (TTBC-Cl) or iodide counterions (TTBC-I) in aqueous solution is investigated by absorption, linear dichroism, and fluorescence spectroscopies, as well as cryogenic transmission electron microscopy (cryo-TEM) and atomic force microscopy (AFM). TTBC-Cl is found to form J-aggregates with a classical Davydov-split absorption band (type I spectrum) even under different preparation conditions. These aggregates remain stable for months. Unlike the chloride salt, the iodide salt TTBC-I forms two different types of J-aggregates depending on the pH of the aqueous solution. The TTBC-I aggregates prepared in pure water (pH = 6) are characterized by a single redshifted absorption band (type III spectrum), whereas those prepared in alkaline solution at pH = 13 show a typical Davydov-split (type I) absorption band. Despite differences in counterions, preparation method, stability, and spectroscopic behavior, cryo-TEM reveals an identical tubular architecture for all these J-aggregates. Among the new structure models discussed here is a cylindrical brickwork layer of dye molecules for single-banded J-aggregates (type III). For Davydov-split aggregates (type I), a molecular herringbone-like pattern is proposed instead. Moreover, absorption spectra have revealed an additional single redshifted absorption band (type II spectrum) that is assigned to a surface aggregate and is induced by a specific interaction of the dye cation with the negatively charged cuvette wall. AFM measurements of analogous preparations on negatively charged mica surfaces have supported this interpretation and revealed the formation of monolayered sheet structures.

Manifestation of Exciton-Lattice Interaction in J-Aggregates

The inverse correlation between the exciton-lattice interaction strength and the exciton delocalization length is shown for dielectric organic nanoclusters – J-aggregates. Since the exciton delocalization length defines all optical properties of J-aggregates, it allows one to control them via the exciton-lattice interaction. We demonstrate the exciton self-trapping suppression in amphi-PIC J-aggregates as a result of the exciton-lattice interaction weakening due to the formation of a surfactant shell around J-aggregates. The control over optical properties via the exciton-lattice interaction for other types of J-aggregates is discussed.

Spectral properties and structure of the J-aggregates of pseudoisocyanine dye in layered silicate films

Hybrid films composed of pseudoisocyanine (PIC) and layered silicates were prepared by direct adsorption from dye solution. Properties of the films were characterized by absorption and fluorescence spectroscopy, which indicated the formation of two types of J-molecular aggregates. Molecular arrangement and structure of the J-aggregates were investigated by means of linearly polarized absorption spectroscopy and X-ray diffraction (XRD). Structural models of the two main types of J-aggregates with oblique and those of parallel molecular alignments were designed. The spectral properties of these species were studied in detail. All the films contained a mixture of both types of the J-molecular assemblies. Predominance of either species likely depends on the layer charge of the silicate template.

Structure investigations on assembled astaxanthin molecules

The carotenoid r,r-astaxanthin (3R,3′R-dihydroxy-4,4′-diketo-β-carotene) forms different types of aggregates in acetone–water mixtures. H-type aggregates were found in mixtures with a high part of water (e.g. 1:9 acetone–water mixture) whereas two different types of J-aggregates were identified in mixtures with a lower part of water (3:7 acetone–water mixture). These aggregates were characterized by recording UV/vis-absorption spectra, CD-spectra and fluorescence emissions. The sizes of the molecular assemblies were determined by dynamic light scattering experiments. The hydrodynamic diameter of the assemblies amounts 40nm in 1:9 acetone–water mixtures and exceeds up to 1μm in 3:7 acetone–water mixtures. Scanning tunneling microscopy monitored astaxanthin aggregates on graphite surfaces. The structure of the H-aggregate was obtained by molecular modeling calculations. The structure was confirmed by calculating the electronic absorption spectrum and the CD-spectrum where the molecular modeling structure was used as input.

Measuring molecular aggregates in sub-attomolar solutions

This contribution presents fluorescence spectra of monomer and assembled tetratolylporphyrin molecules in ultralow concentrated solutions. The molecules were dissolved in acetone. Fluorescence signals could be detected from solutions whose concentration ranged from 10 −14 to 10 −19 M. The detection limit of molecular fluorescence emissions was found at 10 −20 M. The molecular assemblies could be determined as J-aggregates in which the monomer units are shared along the y-axis (N–H⋯H–N) of the porphyrin coordinate system. Two different types of J-aggregates are present. One type appeared in freshly prepared solutions only and turned into the second stable form after few hours.

Photo-induced reorganization of molecular packing of amphi-PIC J-aggregates (single J-aggregate spectroscopy)

Confocal luminescence microscopy has been used to excite and collect luminescence from single amphi-PIC J-aggregate. Two types of J-aggregates have been revealed in the luminescence image: bead-like J-aggregates, which diameter is less than 1 μm and rod-like ones, which length is about 3 μm and diameter is less than 1 μm. It has been found that single rod-like and bead-like J-aggregates exhibit different luminescence bands with different decay parameters. At the off-resonance blue tail excitation, the J-aggregate exciton luminescence disappeared within a certain time period and a new band appeared, which cannot be attributed to the monomer emission. The luminescence image shows that the J-aggregate is not destroyed. However, J-aggregate storage in darkness does not recover its exciton luminescence.

Supramolecular Structure of J-Aggregates of a Sulfonate Substituted Amphiphilic Carbocyanine Dye in Solution: Methanol-Induced Ribbon-to-Tubule Transformation

Replacing the pH-sensitive carboxyl substituents of amphiphilic 5,5',6,6'-tetrachlorobenzimidacarbocyanine dyes by sulfonyl substituents promotes the formation of novel types of J-aggregates in aqueous solution. However, due to the dramatically reduced solubility of the examined 3,3'-bis(2-sulfoethyl)-5,5',6,6'-tetrachloro-1,1'-dioctylbenzimidacarbocyanine (abbreviated as C8S2), aggregation in water can only be triggered by predissolution of the dye in organic solvents (e.g., methanol), the addition of surfactant (SDS), or thermal treatment. Depending on the particular preparation method used, different aggregation behavior was observed by spectroscopic and microscopic studies. Effects of methanol were studied in detail. Below a methanol concentration of ∼3.5%, the absorption spectrum shows a 2-fold split J-band (type II spectrum) characteristic for tubular structures. Above ∼3.5%, the spectrum is characterized by a pronounced H- and a related narrow J-band (type I spectrum) as observed for molecular aggregates with two dye molecules per unit cell (Davydov splitting). Cryo-transmission electron microscopy (cryo-TEM) revealed tubules or stacks of bilayered ribbons as the prototypical morphologies at low and high methanol concentration, respectively. By changing the methanol content of the solutions, a transition between either structures could be induced. The extremely slow kinetics allows the observation of hybrid-aggregates combining the different structural motifs within one individual entity.

Relaxation and trapping of excitons in J-aggregates of a thiacarbocynine dye

Abstract Exciton relaxation processes in J-aggregates of 3,3′,9-triethyl-5,5′-dichlorothiacarbocyanine iodide (TDC) dye have been studied by means of site-selective, steady-state and time-resolved spectroscopy. We found that TDC forms three different types of J-aggregates (J1,J2, and J3) in frozen solutions. Fluorescence polarization measurements showed that exciton diffusion between randomly oriented segments of aggregates plays a minor role in exciton relaxation. Optical properties of J3-aggregate fluorescent states are well described by the theoretical model of barrierless self-trapping of an excitation in a strictly one-dimensional discrete lattice. Upon optical excitation J3-aggregates also show thermally activated transformation to J2-aggregates. The height of the related potential barrier is approximately equal to 30 cm−1. Hence, two different exciton relaxation processes are proposed to take place in the system under study: barrierless self-trapping in J3-aggregates and thermally activated J3 → J2 photorearrangement.

Spectroscopic studies on aggregation of squarylium dyes and the photopolymerization of a diacetylenic derivative in monolayers at the air/water interface

Molecular orientation and aggregation forms of squarylium dyes and also photopolymerization of an amphiphilic diacetylene derivative containing ferrocene, namely heptadeca-2,4-diynylferrocene carboxylate (FcDA), in monolayers at the air/water interface have been investigated by measurements of UV-visible spectra in situ. The aggregation forms of the dyes in the monolayers can be controlled by altering the position and the length of the substituted alkyl chains, as well as by changing the subphase temperature and the surface pressure. Two types of J-aggregates were obtained with bis(dipropylaminophenyl)squarylium dye, depending on the pressure and the temperature, while almost pure H-aggregate could be obtained with bis(dibutylaminophenyl)squarylium dye under high compression at 20°C. Further, the polymerization of FcDA together with the resultant polymer structure are significantly influenced by the orientation and packing of the monomer molecules in the monolayer. Suitably close packing with ordered arrangements of the monomer molecules at higher pressure and lower temperature produced the blue form of the polymer, while rather loosely packed monomer molecules with some conformational freedom at lower pressure and higher temperature gave the red form of the polymer.

Five Types of J-Aggregates in Single-Chain Merocyanine Langmuir Monolayers on an Aqueous Subphase

Abstract The formation of J-aggregates in Langmuir monolayers of a neat merocyanine dye (3-carboxymethyl-5-[2-(3-octadecyl-2-benzothiazolinyldene)ethylidene]-2-thioxo-4-thiazolidinone) has been examined by measuring the normal incidence absorption spectra. Five types of J-aggregates were found to be formed, depending on the temperature and the concentration and type of cations present in the subphase. The shift in the absorption peak wavelength on the J-aggregates formation is accounted for in terms of the number and the geometrical arrangement of the chromophores in each J-aggregate. The spectral shifts were analyzed numerically using both a point dipole model and a transition density model. These calculations indicate that the five different J-aggregates are linear ones with aggregation numbers ranging from 2 to 6.

Generation of the displacement current by the transformation of J-aggregates in spreading monolayers of squarylium dye

Maxwell displacement currents generated from monolayers of squarylium dye with propyl groups (SQ) and from mixed monolayers with arachidic acid were investigated during the course of monolayer compression in connection with the formation of J-aggregates in the monolayers. Abrupt changes in the generation of displacement current were observed for monolayers of SQ due to the transformation between two types of J-aggregates with different absorption spectra. In contrast, for mixed monolayers with arachidic acid which show no transition of J-aggregates, abrupt changes in the displacement current were not observed. It was concluded that displacement current measurement is effective in the detection of the transformation of the molecular arrangement in aggregates.

Multipiled monolayer assembly of J-aggregates of squarylium dye with short alkyl chains

The first observation of J-aggregates of squarylium dyes with short alkyl chains has been made in the monolayer. As the temperature of the aqueous subphase increases, two types of J-aggregates of squarylium dyes with short alkyl chains are formed on the surface and J-aggregates in the monolayer reversibly exchange with each other, depending on the surface pressures and temperatures. In a mixed monolayer with a fatty acid, either an ordinary structure or a multipiled structure is formed by controlling surface pressure. The monolayer assembly with a multipiled structure of dyes is formed under higher surface pressure through phase transition and successively transferred to solid substrates by the Langmuir-Blodgett technique. The multipiled structure of the mixed monolayer is characterized as a triple layer of J-aggregates of squarylium dyes stabilized with a fatty acid monolayer by π- A isotherms, spectroscopic measurements and X-ray diffraction.