Two-photon fluorescence spectroscopy of individually trapped pseudoisocyanine J-aggregates in aqueous solution

We have investigated a pseudoisocyanine dye aqueous solution including nanometer-sized J-aggregates by combining optical trapping and two-photon fluorescence spectroscopy. By focusing an intense near-infrared laser into an 8 x 10(-3) M solution, the intense fluorescence from J-aggregates for a few to tens of seconds is observed intermittently, indicating that individual J-aggregates are trapped in and diffuse out from a focal spot. The peak position and full width at half-maximum of the J-band are different from each other. By measuring 171 J-aggregates, it was found that J-aggregates can be classified largely into two groups. The existence of two kinds of groups of J-aggregates could be attributed to the difference in the nucleation process, which is affected by the substrate. J-aggregates possessing a J-band of a narrower bandwidth in a shorter wavelength region are trapped for a longer period of time, indicating that highly ordered J-aggregates are trapped for a longer period of time because of their high polarizability.     

Picosecond kinetics and transient spectra of pseudoisocyanine monomers and J-aggregates in aqueous solution

Bleaching of monomer and J-aggregate bands of pseudoisocyanine was observed using tunable excitation wavelengths. Both bleached bands decrease with (15 ± 3) ps. A residual J-band bleaching exists up to 1 ns. A new transient absorption in superposition with the J-band was round to consist of two bands with different time behaviour.     

Mega three-photon absorption cross-section enhancement in pseudoisocyanine J-aggregates

Herein we report an extraordinary three-photon absorption cross-section (sigma'3) enhancement in J-aggregates supramolecular systems. The much higher value of sigma'3 in PIC J-aggregate (2.5 x 10(-71) cm6 s2 ph(-2)) compared to typical values obtained in organic molecules (10(-80) cm6 s2 ph(-2)) is attributed to the strong molecular transition dipole moment coupling in the supramolecular assembly. Three-photon absorption of PIC J-aggregates and monomer aqueous solutions were measured using the well known open aperture Z-scan technique pumping with a 25 ps pulse laser-OPG system at 1720 nm. This novel result opens new expectations for applications of supramolecular systems in bioimaging and medicine.     

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

Monolayer behavior of an ion pair amphiphile (IPA), hexadecyltrimethylammonium-dodecylsulfate (HTMA-DS), with normal long-chain alcohols at the air/water interface was analyzed by the Langmuir trough technique with the Brewster angle microscope (BAM) observations, and the pronounced stability enhancement of a HTMA-DS monolayer with the presence of the alcohol additives was demonstrated. Two normal long-chain alcohols with alkyl chain lengths of C16 and C18, 1-hexadecanol (HD) and 1-octadecanol (OD), were chosen as the additives. The surface pressure-area and surface potential-area isotherms of the monolayers with BAM images of monolayer morphology implied that the addition of either HD or OD with a comparatively small head group in a double-chained HTMA-DS monolayer at the interface led to better molecular packing and attractive interaction between the molecules, showing a similar condensing effect as that observed in mixed phospholipid/cholesterol systems. Moreover, the monolayer hysteresis and relaxation curves indicated that the incorporation of the alcohols into a HTMA-DS monolayer was able to lessen the monolayer hysteresis and to enhance the monolayer stability. In comparison with OD, HD seemed more effective as an additive in stabilizing a HTMA-DS monolayer, most likely due to the relatively better molecular packing of HTMA-DS and HD molecules at the interface. It is inferred that the stability of a monolayer or vesicular bilayer structure composed of IPAs can be improved by adjusting the molecular packing/interaction with a suitable long-chain alcohol as the additive.     

Porphyrin J-aggregates stabilized by ferric myoglobin in neutral aqueous solution

J-aggregates of a diacid form (H4TPPS2-) of 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin (H2TPPS4-) were stabilized by binding with ferric myoglobin (metMb) in aqueous solution at neutral pH. The J-aggregates gradually dissociated to monomeric H2TPPS(4-). The average half-lifetime (t1/2) of the J-aggregates in the presence of sufficient amounts of metMb was ca. 3 h in phosphate buffer at pH 7.0 and 25 degrees C. The stabilization of the J-aggregate by metMb is ascribed to encapsulation and fixation of an edge-to-edge structure of the J-aggregate by the relatively rigid protein molecules. The secondary structure of metMb was altered in some extent in the presence of an excess amount of the J-aggregates while no effect on denaturation of metMb was observed with the H2TPPS(4-) monomer or polyacrylate. The hydrophobic nature of the J-aggregate seems to play an important role for denaturation of metMb. The ability of denatured metMb to bind the azide anion was higher than that of natural metMb. The denaturation of metMb by the J-aggregates seems to induce surfacing of hemin leading to an entropy gain in coordination of the N3(-) anion to the iron(III) center.     

Controlled formation of the two-dimensional TTBC J-aggregates in an aqueous solution

Strong experimental and theoretical evidence was provided on the controlled formation of the two-dimensional J-aggregates that were assembled in the herringbone morphology. The exciton-band structure formation of 1,1',3,3'-tetraethyl-5,5',6,6'-tetrachlorobenzimidazolocarbocyanine (TTBC) J-aggregates was investigated in ionic (NaOH) aqueous solution at room temperature. The control was achieved by changing the [TTBC] at a given [NaOH], or vice versa, and was monitored through the changes in the absorption, fluorescence excitation, and emission spectra. Specific attention was paid to expose the excited-state structure and dynamics through simulations of the excitonic properties, which included diagonal energetic disorder and phonon-assisted exciton relaxation. Aggregates were characterized by an asymmetrically split Davydov pair, an H-band (approximately 500 nm, 1300 cm(-1) wide, Lorentzian-like) and a J-band (approximately 590 nm, 235 cm(-1) wide, with a band shape typical of a one-dimensional J-aggregate), whose relative intensities showed a strong dependence on the [TTBC]/[NaOH]. The H-band is favored by high [TTBC] or high [NaOH]. An explanation of the control on the aggregate formation was given by correlating the changes in the absorption with the structural modifications and the subsequent changes in the dynamics, which were induced by variations in the dye and NaOH concentrations. The J-band shape/width was attributed to disorder and disorder-induced intraband phonon-assisted exciton relaxation. The intraband processes in both bands were estimated to occur in the same time scale (about a picosecond). It has been suggested that the wide energetic gap between the Davydov split bands (3000 cm(-1)) could get bridged by the excitonic states of the loosely coupled chains, in addition to the monomeric species at low [TTBC]. Phonon-assisted interband relaxation, through the band gap states and/or directly from the H- to the J-band, are suggested for accounting the difference between the bandwidths and shapes of the two bands. Energy transfer between the H-band and the monomeric species is suggested as crucial for tuning the relative strengths of the two bands.     

Electric field-controlled dissociation and association of porphyrin J-aggregates in aqueous solution

The electrooptic effects of porphyrin J-aggregates of tetraphenyl porphyrin tetrasulfonic acid (TPPS) in aqueous solution were studied using electroabsorption (EA) spectroscopy. When the J-aggregates were three-dimensionally distributed, the EA spectra exhibited broadening in the exciton band. When a DC or AC electric field was applied for a long time, the J-aggregates with KCl were dissociated into monomers via N-mers (N = 2-4) as intermediate states, while those without KCl had an increase in aggregation. The EA spectra showed a red shift in the exciton band for N-mers, which indicates that N-mers are isolated microaggregates with a coherent aggregation number N, and isolated microaggregates have not been microscopically or spectrally observed until now. The estimated third-order nonlinear optical susceptibility χ((3)) for EA spectra in aqueous solution was 10(4) times larger than that in a polymer film. The molecular rearrangement model was applied to a variety of orientational distributions and the results were explained fairly well. The contribution of the electric double layer is the most probable reason for the large enhancement of χ((3)) for the solution sample. The dynamic equilibrium between two types of monomers, J-aggregates of various aggregation numbers and cations such as K(+) and H(+) was investigated to reveal that K(+) is more loosely bound to the constituent monomers in J-aggregates than H(+). Equilibrium equations also show that well-grown aggregates with N > 15 tend to dominate in a solution of J-aggregates, which explains why only well-developed aggregates can be observed spectroscopically.     

Excitons in J-aggregates with hierarchical structure

Unusually sensitive wavelength dependence of hole-burning efficiency in oriented J-aggregates is explained by the hierarchical structure of one-dimensional J-aggregates proposed by us from the experimental results of the concentration dependence of the dichroic spectra.     

Magnetochiral effects in amphiphilic porphyrin J-aggregates

The detection of magnetochiral dichroism (MChD; CD: circular dichroism) in a suspension of J-aggregate particles of an achiral amphiphilic nonmetalated porphyrin renews the interest for porphyrins in supramolecular chemistry and reinforces the concept that novel advanced materials can be obtained through self-assembly and auto-organization processes (see picture).     

Substituent-control exciton in J-aggregates of protonated water-insoluble porphyrins

A series of protonated porphyrin J-aggregates of various water-insoluble tetraphenylporphyrin derivatives was prepared by aggregation at the liquid-liquid or gas-liquid interface. Using atomic force microscopy, we observed microcrystalline porphyrin J-aggregates. The J-aggregates have two strong exciton bands corresponding to the B (Soret)- and Q-bands of the protonated porphyrin. Interestingly, the excitation energy of the lower exciton (denoted by S1) markedly depends on the meso-substituents, whereas that of the higher exciton (denoted by S2) does not depend on them. These results indicate that the nature of the exciton coupling of the S1 transition dipole moment can be systematically changed by the substituents.     

Tuning J-aggregates of tetra(p-hydroxyphenyl)porphyrin by the headgroups of ionic surfactants in acidic nonionic micellar solution

J-aggregates of the diacid form of tetra(p-hydroxyphenyl)porphyrin (THPP) were found to be stable in nonionic micellar solution in the presence of trace ionic surfactant with an oxyacid headgroup. The excitation energy of exciton coupling depends systematically on the headgroups of the ionic surfactant, by which strong and weak coupling can be accomplished in the J-aggregates. The J-aggregates have two strong exciton bands corresponding to the B- and Q-bands of the protonated monomers. The total fluorescence of THPP is quenched through aggregate formation. A strong and sharply peaked resonance light-scattering signal that suggests a delocalized excitonic state was observed just slightly to the red of the absorption maximum of the J-aggregates. The overall resonance Raman intensities appeared to be stronger in the aggregates than in the monomers. In the kinetics of aggregation induced by sodium dodecyl sulfate (SDS), no characteristics of autocatalyzed reactions were observed, and there was only a logarithmic phase that lasted only several seconds.     

J-aggregates in matrix stabilized two-dimensional azobenzene derivatives

A two-component film technique at the air-water interface has been used for fabricating matrix stabilized azobenzene J-aggregates. Langmuir monolayers of (E)-1-(3-chloro-4-(alkyloxy)phenyl)-2-phenyldiazene (CnCD, n=8,10,12) have been prepared with stearic acid (STA) as the two-dimensional matrix. Miscibility studies at a molecular level, explored from the monolayer pressure-area isotherms revealed a phase separation of the CnCD from the stearic acid matrix at a compression pressure of 10 mN/m. A 43-nm strong red shift in the 350 nm pi-pi * absorption feature implied formation of highly ordered J-aggregates of CnCDs in conformity with atomic force microscopy and micro-Raman spectral characteristics. While a one-component CnCD failed to form a 2D monolayer, the STA supported CnCD binary system crossed a mixed monolayer phase followed by compression, leading to the formation of matrix stabilized CnCD J-aggregates.     

Two-photon absorption of a supramolecular pseudoisocyanine J-aggregate assembly

Linear spectral properties, including excitation anisotropy, of pseudoisocyanine or 1,1′-diethyl-2,2′-cyanine iodide (PIC) J-aggregates in aqueous solutions with J-band position at 573 nm were investigated. Two-photon absorption of PIC J-aggregates and monomer molecules was studied using an open aperture Z-scan technique. A strong enhancement of the two-photon absorption cross-section of PIC in the supramolecular J-aggregate assembly was observed in aqueous solution. This enhancement is attributed to a strong coupling of the molecular transition dipoles. No two-photon absorption at the peak of the J-band was detected.     

Two-photon absorption enhancement of polymer-templated porphyrin-based J-aggregates

Supramolecular structures based on organized assemblies of macrocyclic chromophores, particularly porphyrin-based dyes, have attracted widespread interest as components of molecular devices with potential applications in molecular electronics, artificial light harvesting, and pharmacology. We report the formation of J-aggregates of two porphyrin-based dyes, 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin (TSPP, 4) and an amino tris-sulfonate analogue (5) in water using a functionalized norbornene-based homopolymer, synthesized by ring-opening metathesis polymerization (ROMP). Ionic interactions of the cationic side chains (ammonium groups) of the polymer under acidic conditions with the negatively charged sulfonate groups of the porphyrins facilitated polymer template enhanced J-aggregation of the porphyrin dyes. J-Aggregation behavior was investigated photophysically by UV-vis absorption along with steady-state and time-resolved fluorescence studies. Two-photon absorption (2PA) was enhanced by about an order of magnitude for the J-aggregated TSPP relative to its free base. Significantly, the 2PA cross section of the polymer-templated TSPP J-aggregate was up to three times higher than the J-aggregated TSPP in the absence of the polymer template while the 2PA cross section for polymer-templated J-aggregates of 5 increased substantially, up to ca. 10,000 GM, suggesting a prominent role of polymer-templating to facilitate porphyrin aggregation and greatly enhance nonlinear absorption.     

J-aggregates in vapor deposited films of a bisazomethine dye

This is the first report of J-aggregate formation of a non-ionic bisazomethine dye in vapor deposited films; this dye allows us to prepare easily large homogeneous and very stable J-aggregate thin films and to investigate intrinsic properties of low-dimensional Frenkel excitons.     

Unusual optical properties of porphyrin fractal J-aggregates

A simple mix and shake procedure in aqueous solution from water-soluble tetrakis(4-sulfonatophenyl)porphyrin and spermine leads to fractal non-covalent supramolecular systems which exhibit unusual large enhancement of resonant light scattering, behaving as metal particles.     

Chiral assembly of achiral pseudoisocyanine with D- and L-phenylalanine

Supramolecular chirality and molecular self-assembly are important and interesting phenomena in living and non-living systems.In this work,supramolecular chirality of achiral pseudoisocyanine(PIC) J-aggregates was successfully induced by D-,L-phenylalanine(Phe) and other amino acids in NaCl solution.The chiral J-aggregates showed a characteristic,induced circular dichroism(ICD) in the visible region of J-band chromophore which depends on the absolute configuration,concentration and side groups of α-amino ac...     

A model of the optically active scheibe-aggregate of pseudoisocyanine

A twisted band aggregate, based upon a brickwork arrangement of monomers, seems to be a reasonable model for the optically active Scheibe-aggregate of pseudoisocyanine.     

D-，L-苯丙氨酸诱导非手性菁染料的手性组装

超分子手性与分子自组装是生命体中非常重要和有趣的现象．报道了D,L-苯丙氨酸等氨基酸在氯化钠溶液中通过非共价键相互作用诱导非手性菁染料（Pseudoisocyanine,PIC）J-聚集体超分子手性的形成．实验结果表明,诱导的手性菁染料PIC聚集体发色团在π-π^＊跃迁区域产生了特征的镜像圆二色性,其圆二色信号和强度强烈地依赖于氨基酸的绝对构型、浓度、侧链基团和溶液温度．原子力显微镜照片清楚地表明,^聚集体由相互交联的纳米纤维组成,诱导的圆二色性可能来源于纤维状聚集体的宏观螺旋排列．