TRIPLET YIELD OF MEROCYANINE 540 IN WATER IS WAVELENGTH DEPENDENT

Monomers and aggregates of Merocyanine 540 (MC540) in water are able to photoisomerize. The shape of the photoisomer absorption spectrum is very similar to that of the ground state. Triplet state of MC540 in water has been produced by energy transfer from triplet anthracene and displays a broad absorption spectrum between 600 and 700 nm. The triplet state may also be produced by direct excitation of MC540 with UV light. However, when the dye is excited by visible light, no triplet state absorbance in the red could be detected so that the triplet yield of MC540 in water seems to be excitation wavelength dependent.     

Optical limiting of gold nanoparticle aggregates induced by electrolytes

The electronic absorption spectra and optical-limiting (OL) properties of gold nanoparticle (AuNP) aggregates induced by KCl and NaCl have been investigated using 4.1-ns laser pulses at 532 nm. Although the individual AuNP colloid shows no optical-limiting effect, the AuNP aggregates exhibit significant optical-limiting characteristics. With an increased concentration of KCl and NaCl, the surface plasmon resonance (SPR) band shifts to a longer wavelength, and the optical-limiting performance is enhanced. Both the electronic absorption and optical limiting are influenced by the particle size. The larger the individual nanoparticle, the further red-shifted the SPR band and the stronger the optical limiting. Optical limiting of aggregates induced by KCl is stronger than that of aggregates induced by NaCl. Mechanistic studies reveal that free-carrier absorption is the dominant contributor to the optical limiting, with negligible contribution from nonlinear scattering.     

Self-association of uracil in aqueous solution. Study of dilute solutions by normal and second derivative UV absorption spectroscopy.

Normal and second derivative UV absorption spectra of dilute aqueous solution (5x10⁻⁶ − 5x10⁻³ M) of uracil at neutral pH have been registered. Concentration dependence of spectral parameters, molar absorptivity, maxima position, full width at half-height (FWHH) and band asymmetry at ∼202 nm and 258 nm have been studied. Both bands show hyper- and hypo-chromic effects as concentration increases. These effects indicate the formation of different aggregates due to uracil-water interactions and stacking self-association. From the isodesmic model, the apparent self-association constants have been obtained :

from the first and second hypochromic effects, respectively.     

Spectroscopic analysis of the interaction of a peptide sequence of Hepatitis G virus with bilayers

Merocyanine 540 (MC540) has been used as external probe to determine the interaction of the peptide sequence 125-139 corresponding to the E2 protein of Hepatitis G virus, with lipid bilayers. The probe was incorporated into large unilamellar vesicles (LUVs) or small unilamellar vesicles (SUVs) of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC). When incorporated into bilayers, MC540 shows two absorption maxima corresponding to the monomer (570 nm) and dimer (530 nm) form of the probe. Changes in the probe microenvironment are reflected by a modification in the position and/or intensity of these maxima. Addition of increasing amounts of peptide resulted in a slight decrease of the ratio A570/A530 thus indicating a change in MC540 partition into the membrane, going from a hydrophobic to a more hydrophilic environment. This effect was concomitant with an increase in dimer formation as stated from the values of the apparent dimerization constant (K(app)) obtained. Fluorescence spectra as well as steady state anisotropy measurements were in agreement with the above results indicating that the peptide was able to relocate the probe and displacing MC540 from its initial location into the bilayer. Results with SUVs or LUVs were similar for what curvature does not seem to play any role on peptide activity. These results reflect the ability of peptide to interact with biomimetic membranes in the lipid head group region.     

Influence of aggregation on the phosphorescence of iridium complex in poly(methyl methacrylate) matrix

In this study, novel phosphorescent compound of iridium(III)bis(2,3‐diphenylquinoxaline)2‐(benzoimidazol‐2‐yl)pyridine (IrQB) was prepared and the emission study suggests the solid form of IrQB has less phosphorescence intensity than its solution in tetrahydrofuran (THF). To avoid the potential aggregation of IrQB in the concentrated state, poly(methyl methacrylate) (PMMA) was intentionally added as isolator to make solutions of different concentrations in THF and then solid films of IrQB/PMMA of different compositions after THF removal. Films of IrQB/PMMA prepared from dilute solutions exhibit two emission bands centered at 540 and 640 nm, respectively, which is in contrast to the sole 640‐nm emission band observed for films prepared from semidilute solutions. The 540‐ and 640‐nm bands show progressive variations of the intensity with temperature. Emission band at 540 nm is derived from the polarized optical microscope and is attributed to the IrQB aggregates, whose life‐time indicates it is phosphorescent in nature. This aggregate formation is strongly affected by the applied concentrations of IrQB and PMMA in the preparative solution state. Model to postulate the mechanism of aggregate formation in the solution and the derived film states is thereby presented in this study. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 631–639, 2008     

On the dynamics of the TPPS4 aggregation in aqueous solutions: successive formation of H and J aggregates

The dynamics of aggregation of meso-tetrakis (p-sulfonatofenyl) porphyrin (TPPS4) in function of its concentration, pH and ionic strength was studied by optical absorption, fluorescence and resonance light scattering (RLS) techniques. In the region of pH, where TPPS4 exists in biprotonated form, the addition of NaCl induces the TPPS4 aggregation due to the formation of the "cloud" of counter ions around the TPPS4 molecule thus reducing electrostatic repulsion between the porphyrin molecules. The formation of this "cloud" shifts the pKa value to acid region (from 5.0 in the absence of salt to 4.5 at [NaCl] = 0.4 M), reduces the TPPS4 absorption in all spectral range and quantum yield and lifetime of fluorescence (from 0.27 to 0.17 and from 4.00+/-0.04 to 3.00+/-0.03 ns in the absence of salt and in the presence of NaCl, respectively). The aggregation process involves two successive stages: initially H aggregates are formed, which in time are transformed in J ones. The existence of these two stages was confirmed by the fluorescence and RLS data. The kinetics of the formation of J aggregates is characterized by the induction time t1 and the average growth time t2, which depend on both TPPS4 and salt concentrations. The induction period t1 appears as a result of initial formation of H aggregates and their successive transformation in J ones. At very high TPPS4 concentrations, the J aggregates are united in more complex structures such as hollow cylinders or helixes.     

Counterion dependent dye aggregates: nanorods and nanorings of tetra(p-carboxyphenyl)porphyrin

Atomic force microscopy (AFM) of porphyrin aggregates formed on silica from acidic aqueous solution is used to investigate the basis for the previously reported counterion dependence of the optical spectra of aggregates of H(2)TCPP(2+), the diacid form of tetra(p-carboxyphenyl)porphyrin (TCPP). Resonance light scattering confirms the presence of excitonically coupled porphyrin aggregates in solutions of H(2)TCPP(2+) in both aqueous HCl and HNO(3). Aggregates formed in aqueous HNO(3) solutions show resonance light scattering (RLS) at wavelengths within both the H and J aggregate absorption bands and are imaged on the surface of silica as nanorods about 3 to 4 nm in height. H(2)TCPP(2+) aggregates in aqueous HCl solution exhibit RLS when excited within the blue-shifted Soret band (H band) and produce AFM images on silica of ring-shaped structures ranging from about 200 to 2000 nm in diameter. Fluorescence excitation and emission spectra reveal quenching of the Q-band emission in the aggregates at a pH less than 1 and confirm the existence of a single species, assigned to a dimer, at a pH just above 1. The morphology of the nanostructures as revealed by AFM provides insight into the structural basis for the counterion-dependent optical properties of H(2)TCPP(2+) aggregates.     

A spectroscopic study of the fluorescence quenching interactions between biomedically important salts and the fluorescent probe merocyanine 540

The effects of several biologically important inorganic salts, including NaCl, NaI, NaBr, KCl, MgCl2, MgSO4 and CaCl2 on the electronic absorption and fluorescence spectra of Merocyanine 540 (MC-540) have been investigated in aqueous media at 25 degrees C. Depending on both the MC-540 concentration and the nature of salt, a new absorption band appears at about 515 nm, above the critical salt concentration (CSC), corresponding to salt-induced MC-540 aggregation. Several types of MC-540 fluorescence quenching by the salts are observed, according to their cationic charge and the nature of anion: in the case of monovalent ions (Na+, K+), a non-linear Stern-Volmer behaviour is observed, indicating variable contributions of dynamic and static quenching mechanisms, whereas for divalent alkaline-earth (Mg2+, Ca2+) ions, linear Stern-Volmer relationships are obtained. Using these results, an analytical quenchofluorimetric approach is proposed for the determination of magnesium ions.     

CuC_2O_4多孔球的可控合成

采用温和水溶液法,以CuCl2.2H2O和H2C2O4.2H2O为原料合成了新颖结构的CuC2O4多孔球。产物结构与形貌用X射线衍射、扫描电子显微镜测试技术进行了表征。研究了反应温度、反应物浓度、不同体积阴离子等对产物形貌与尺寸的影响。结果表明,单斜结构的CuC2O4多孔球直径为400～540nm,每个多孔球由50～80nm的纳米粒子自组装而成。反应物浓度及阴离子体积能调节纳米粒子的团聚尺寸,而反应温度可有效地调节多孔球的尺寸。刻蚀过程解释了CuC2O4多孔球的形成机理。     

Steps to demarcate the effects of chromophore aggregation and planarization in poly(phenyleneethynylene)s. 2. The photophysics of 1,4-diethynyl-2-fluorobenzene in solution and in crystals

Crystals of 1,4-bis(2-hydroxy-2-methyl-3-butynyl)-2-fluorobenzene 4 have a rich packing structure with four distinct molecules in the unit cell. A complex hydrogen bonding network results in the formation of cofacial trimers, cofacial dimers, and monomers within the same unit cell. Given a remarkable opportunity to investigate the effect of aggregation on the photophysics of 1,4-diethynylbenzenes, we analyzed the absorption, diffuse reflectance, and emission spectra of compound 4 in solutions and in crystals. Diffuse reflectance and fluorescence excitation revealed a red-shifted absorption that is absent in dilute solution but becomes observable at high concentrations and low temperatures. The fluorescence emission in the solid state is dual with components assigned to monomers and aggregates. The excitation and emission assigned to the monomer are nearly identical in crystals and dilute solutions. The absorption and emission bands assigned to aggregates are broad and red-shifted by 60--80 nm. As expected for a sample with absorbers and emitters with different energies and incomplete equilibration, efficient monomer-to-aggregate energy transfer was observed by a proper selection of excitation wavelengths. The fluorescence quantum yield of 4 in solution is relatively low (Phi(F) = 0.15) and the singlet lifetime short (tau(F) = 3.8 ns). A lower limit for the triplet yield of Phi(T) = 0.64 was determined indirectly in solution by (1)O(2) sensitization, and a relatively strong and long-lived phosphorescence was observed in low-temperature glasses and in crystals at 77 K.     

Interactions of cyanine dyes with nucleic acids. XXIV. Aggregation of monomethine cyanine dyes in presence of DNA and its manifestation in absorption and fluorescence spectra.

Absorption, fluorescence emission and excitation spectra of benzothiazole cyanine dyes--thiazole orange (TO) and 7-methyl-6-(3-methyl-2,3-dihydro-1,3-benzothiazol-2-ylidenmethyl) [1,3] dioxolo [4',5':4,5] benzo [d] [1,3] thiazolium methylmethosulfate (Cyan 13)--were investigated over a wide concentration range. The dyes form aggregates with a 'sandwich'-like structure in water solution. At low dye to DNA concentrations ratios, Cyan 13 and TO monomers appear to interact with the DNA. On increasing the dye to DNA concentrations ratio, free dye molecules aggregate with the DNA-bound ones. The spectra of the free dye aggregates and the aggregates formed on the DNA, are characterized by an anomalously large (more than 100 nm) Stokes shift. This suggests, that the pi-electron systems of the aggregates undergo substantial changes in excited state, compared to those of the monomers. The formation of aggregates consisting of the free and DNA-bound dye molecules can be explained using the half-intercalation model of the interaction of the cyanine dye monomers with the DNA.     

Excited-state dynamics of spiropyran-derived merocyanine isomers

Merocyanine (MC) isomers that are formed after absorption of a UV photon by 1',3'-dihydro-1',3'-3'-trimethyl-6-nitrospiro[2H-1-benzopyran-2',2'-(2H)-indole] were studied. Several, predominantly TTC and TTT, merocyanine isomers are present in toluene solution ("T" and "C" indicate trans and cis conformations of the C-C bonds in the methine bridge). Excitation in the MC visible absorption band (at 490, 550, and 630 nm) with 100 fs laser pulses was used to study MC excited-state dynamics. Internal conversion on the picosecond time scale was found to be the dominant relaxation pathway. Excited-state isomerization reactions were also observed. Excitation at 630 nm (assigned to TTC isomer excitation) leads to formation of a third isomer (either CTC or CTT). Excitation at 490 nm (assigned to TTT isomer excitation) leads to more complex excited-state relaxation, including formation of two isomers: TTC (absorption at 600 nm) and CTC or CTT (absorption at 650 nm).     

Investigation on DNA assembly to neutral red-cyclodextrin complex by molecular spectroscopy

DNA assembling to neutral red (NR) and cyclodextrins (CDs)-NR inclusion complex has been investigated by means of absorption, fluorescence and resonance light scattering (RLS). Depending on the molar ratio R of NR:DNA, the binding of NR with DNA involved in two processes at pH 7.50 and ionic strength 0.0045. The first process occurs in R>2.5, where the neutral form of NR was predominant and enhanced RLS was observed, indicating the aggregation of NR neutral form molecules on the molecular surface of DNA. The second process occurs in R<2.5, where an absorption band at 540 nm and a fluorescent excitation and emission band at 550 and 607 nm respectively provided compelling evidence that the binding of NR to DNA leaded to extensive NR protonation even at pH 7.50, and that a protonated NR (the acidic form of NR) can form DNA adducts with a binding mode different from that of the unprotonated form (the neutral form of NR). The results were also illustrated by the CDs-NR supramolecular system. The experimental data showed that CDs including beta-CD, hydroxypropyl-beta-CD (HP-beta-CD) and sulfobutylether-beta-CD (SBE-beta-CD) superior to include the neutral form of NR, in addition, the inclusion complex decomposed when it bound to DNA. Thus, the decomposed NR was also protonated to form DNA adducts with intercalative mode. In fact, CDs played a role to carry guest molecule to intercalate DNA. A related mechanism is proposed.     

Modulation of cyanobacterial photosystem I deposition properties on alkanethiolate Au substrate by various experimental conditions

We present results from atomic force microscopy (AFM) images indicating various experimental conditions, which alter the morphological characteristics of self-assembled cyanobacterial PS I on hydroxyl-terminated self-assembled alkanethiolate monolayers (SAM/Au) substrates. AFM topographical images of SAM/Au substrates incubated in solutions containing different PS I concentrations solubilized with Triton X-100 as the detergent reveal large columnar aggregates (～100 nm and hence, much taller than a single PS I trimer) at high PS I concentrations. Depositions from dilute PS I suspensions reveal fewer aggregates and relatively uniform surface topography (～10 nm). Confocal fluorescence microscopy analysis of fluorescently tagged PS I deposited on to SAM/Au substrates using electric field and gravity driven techniques reveal preliminary indications of directionally aligned PS I attachments, besides corroborating a uniform monolayer formation, for the former deposition method. The complex attachment dynamics of PS I onto SAM substrates are further investigated from the AFM images of PS I/SAM/Au substrates prepared under different experimental conditions using: 1) PS I isolated as monomers and trimers 2) adsorption at elevated temperatures, and 3) different detergents with varying pH values. In each of the cases, the surface topology indicated distinct yet complex morphological and phase characteristics. These observations provide useful insight into the use of experimental parameters to alter the morphological assembly of PS I on to SAM substrates en route to successful fabrication of PS I based biohybrid photoelectrochemical devices.     

Subcellular localization of merocyanine 540 (MC540) and induction of apoptosis in murine myeloid leukemia cells

Subcellular localization of photosensitizers is thought to play a critical role in determining the mode of cell death after photodynamic treatment (PDT) of leukemia cells. Using confocal laser scanning microscopy and fluorescent organelle probes, we examined the subcellular localization of merocyanine 540 (MC540) in the murine myeloid leukemia M1 and WEHI 3B (JCS) cells. Two patterns of localization were observed: in JCS cells, MC540 was found to localize on the plasma membrane and mitochondria; and in M1 leukemia cells, MC540 was found to localize on lysosomes. The relationship between subcellular localization of MC540 and PDT-induced apoptosis was investigated. Apoptotic cell death, as judged by the formation of apoptotic nuclei, was observed 4 h after irradiation in both leukemia cell lines. Typical ladders of apoptotic DNA fragments were also detected by DNA gel electrophoresis in PDT-treated JCS and M1 cells. At the irradiation dose of 46 kJ/m2 (LD90 for JCS and LD86 for M1 cells), the percentage of apoptotic JCS and M1 cells was 78 and 38%, respectively. This study provided substantial evidence that MC540 localized differentially in the mitochondria, and the subsequent photodamage of the organelle played an important role in PDT-mediated apoptosis in myeloid leukemia cells.     

Computer simulation of band shapes in electronic absorption spectra of dimers of organic dyes

The band shapes in the absorption spectra of dimers of cyanine dyes were simulated using a combination of an empirical molecular force field for the ground state with quantum-chemical calculations of the electron excitation energy as a function of normal nuclear coordinates. The shape and the width of an absorption band strongly depend on the mutual arrangement of the monomers. If the monomers are located one directly above the other, the sublevels arising from intramolecular vibrations disappear in the spectrum, and a large hypsochromic shift of the 0-0-transition band is observed, which results mainly from through-space interaction of monomer orbitals. If the monomers are strongly shifted relative to each other, the sublevels mentioned are also absent in the spectrum, but the bathochromic shift of the 0-0-transition band is small and results from interaction of dipole moments of electron transitions. A rather broad region of intermediate structures is found between these dimer forms, where the interaction of dipole moments of electron transitions in monomers is low, and the shapes of absorption bands are similar to those of the monomers.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1705–1710, September, 1995.This work was financially supported by the Russian Foundation for Basic Research (Project No. 94-03-08539) and the International Science Foundation (Grant M1Z 000).     

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.     

四苯硼钠-甲苯胺蓝缔合物纳米微粒体系减色效应研究

在PH4.0醋酸-醋酸钠介质中，甲苯胺蓝在600nm处有一个吸收峰，随着四苯硼钠浓度的增大甲苯胺蓝在600nm处吸收峰降低，颜色减弱，这是由于甲苯胺蓝-四苯硼钠缔合物分子间存在较强的疏水作用及分子间作用力，聚集形成纳米微粒所致，甲苯胺蓝-四苯硼钠纳米微粒体系亦在600mm处有1个吸收峰，在400mm、470mm和580mm处产生3共振散射峰，其中400mm和580mm为甲苯胺蓝-四苯硼钠复合纳米微粒产生的特征共振散射峰，这也表明有纳米微粒存在，丙酮浓度的影响实验结果等表明，纳米微粒的形成是产生其减色效应的原因。     

曙红Y的共振光散射与共振荧光

研究了曙红Y（EY）的共振散射光谱、荧光光谱和吸收光谱,讨论了共振光散射与共振荧光的区别与联系。在EY水溶液三维荧光等高线光谱图中,瑞利散射线与荧光等高线有部分相交。EY的共振散射峰（525nm）介于荧光激发峰（514nm）和发射峰（536nm）之间。由光偏振实验,测得EY共振散射光谱525nm处的偏振度P=0．20。上述实验结果证明,EY的共振散射峰主要是共振荧光。在改变pH的实验中发现,EY共振光散射增强是由于酸碱平衡的移动导致荧光型体的形成。由于自吸收的影响,共振散射光强度与EY浓度之间不是严格的线性关系。     

Behaviours of trinitratonitrosyl complexes of ruthenium in dilute nitric acid solutions (author's transl)

This study aimed to elucidate the protolysis and condensation processes of the Ru complexes in relation to the concentration of nitric acid. The compositions of the dissociated and undissociated complexes were determined by the extraction with tributyl phosphate (TBP) and absorption spectroscopy in order to follow the rather rapid protolysis reaction of the complexes. The test solutions were prepared by dissolving the freshly obtained complexes into 0.50-0.001 M nitric acid solutions. The amounts of the undissociated complexes were determined at different elapses of time in the test solutions. The protolysis became significant when the concentration was below 0.15 M, and the dissociation rate suddenly increased at this concentration. At the concentrations above 0.2 M, the absorption peak of the complexes at 480 nm survived even after 144 hours. But below 0.15 M, the formation of dissociation products by protolysis was observed after the disappearance of the absorption peak. The amount of dissociation products rapidly increased after the preparation of the test solution as the concentration decreased below 0.15 M.