Bathochromic Shift (bathochromic + shift)

Distribution by Scientific Domains

Selected Abstracts

Photochromic Properties of New Benzoindene-Fused 2H -Chromenes

The synthesis and the photochromic properties of new photochromic 6,7- and 7,8-benzoindene annellated benzopyrans are described. When compared to parent indeno-fused 2H -chromenes (2H -[1]benzopyrans), compounds 10 and 12 exhibit a significant bathochromic shift of maximum-absorption wavelength, an increase in the colorability, and similar fading rates. [source]

Coordination of nickel and copper dithiolate to 2,2,-bipyridine-based ,-conjugated polymers

Shin-ichiro Kato
Abstract ,-Conjugated polymers (Poly1,Poly3) containing a 2,2,-bipyridine (bpy) unit were subjected to coordination to nickel and copper dithiolate for the purpose of manipulating the photophysical properties. The absorption maximum peak of Poly1 [maximum wavelength (,max) = 446 nm] redshifted by 36 nm upon the coordination of bpy to NiCl2, which produced Poly1,NiCl2. A further bathochromic shift was observed in the spectrum of Poly1,mntNi [mntNi = (maleonitrile dithiolate)nickel; ,max = 499 nm] bearing the dithiolate ligand, which stemmed from the extension of the conjugated system over the nickel dithiolate moiety through the bpy unit. An increase in the [Ni]/[bpy] ratio in Poly1,mntNi rendered the original maximum peak at 446 nm smaller and the lower energy charge-transfer peak at 499 nm larger; the isosbestic points remained at 380 and 475 nm. The green fluorescence (,max = 504 nm) emitted from Poly1 markedly diminished upon the coordination of nickel dithiolate because of the effective energy transfer. The absorption maximum peak of Poly1,mntNi in chloroform at 499 nm blueshifted to 471 nm when the volume ratio of the chloroform/N,N -dimethylformamide solvent reached 10:90. The coordination of nickel dithiolate to Poly2 and Poly3 also brought about redshifts of the absorption maximum peaks of as much as 55 and 61 nm, respectively. The absorption maximum peak of Poly1,(phenyldithiolate)nickel(pdtNi) (,max = 474 nm) redshifted by 28 nm in comparison with that of Poly1, whereas the magnitude of the shift of Poly1,bis(thiophenoxide)nickel(btpNi) bearing two thiophenoxide ligands was 20 nm. Poly1,mntCu with a tetrahedral copper center was also investigated. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2631,2639, 2004 [source]

Investigations on 1,5-diaminoanthraquinone by laser excitation

M. Umadevi
Abstract Optical absorption and fluorescence emission spectra of 1,5-diaminoanthraquinone (1,5-DAAQ) in different solvents and the surface-enhanced Raman scattering (SERS) spectrum of 1,5-DAAQ in silver sol were investigated. Optical absorption and fluorescence emission studies revealed that the internal and external hydrogen bonds and reorientation of the solvent molecule around the excited state fluorophore are responsible for the observed bathochromic shift and the non-radiative decay process in polar solvents. SERS studies showed that 1,5-DAAQ molecules are chemisorbed through carbonyl groups and the lone pair of electrons on the nitrogen. The orientation of the molecule on the silver surface is found to be stand-on. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Mechanistic comparison of blood undergoing laser photocoagulation at 532 and 1,064 nm

John F. Black PhD
Abstract Background and Objectives We seek to compare and contrast the mechanisms of blood photocoagulation under 532 and 1,064 nm laser irradiation in vitro in order to better understand the in vivo observations. We also seek to validate a finite element model (FEM) developed to study the thermodynamics of coagulation. Study Design/Materials and Methods We study the photocoagulation of whole blood in vitro at 532 and 1,064 nm using time-domain spectroscopic and optical coherence tomography (OCT)-based imaging techniques. We model the coagulation using an FEM program that includes the latent heat of vaporization (LHV) of water, consideration of the pulse shape of the laser, and the bathochromic shift in the hemoglobin absorption spectrum. Results We find significant similarities in the spectroscopic, chemical, and structural changes occurring in hemoglobin and in the blood matrix during photocoagulation despite the very large difference in the absorption coefficients. The more uniform temperature profile developed by the deeper-penetrating 1,064 nm laser allows us to resolve the structural phase transition in the red blood cells (going from biconcave disc to spherocyte) and the chemical transition creating met-hemoglobin. We find that the RBC morphology transition happens first, and that the met-Hb transition happens at a much higher temperature (,>,90°C) than is found in slow bath heating. The FEM analysis with the LHV constraint and bathochromic shift predicts accurately the imaging results in both cases, and can be used to show that at 1,064 nm there is the potential for a runaway increase in absorption during the laser pulse. Conclusions Photothermally mediated processes dominate the in vitro coagulation dynamics in both regimes despite the difference in absorption coefficients. There is a significant risk under 1,064 nm irradiation of vascular lesions in vivo that the dynamic optical properties of blood will cause runaway absorption and heating. This may in turn explain some recent results at this wavelength where full-thickness burns resulted from laser treatment. Lasers Surg. Med. 36:155,165, 2005. © 2005 Wiley-Liss, Inc. [source]

Synthesis of Upper Rim Functionalized Calixarene-Based Poly(norbornenes)

Alaa S. Abd-El-Aziz
Abstract A modified synthesis of 25-allyl-26,27,28-trihydroxycalix[4]arene is reported. This calix[4]arene was utilized to prepare calix[4]arenes containing norbornene and calix[4]arene containing azo dyes and norbornene on their upper rims. The calixarene monomers were reacted with Grubbs' second generation catalyst to give poly(norbornenes) containing calixarenes. The poly(norbornenes) were determined to possess molecular weights between 45,100 and 116,200 with PDIs between 1.4 and 1.9. Thermal analysis showed that the azo dye containing polymers were less thermally stable than the non-azo dye containing polymers with decompositions beginning at 140,°C and 395,°C, respectively. The azo dye containing polymers displayed ,max at 430,nm in THF solutions that underwent a bathochromic shift to 520,nm when acidified with HCl(g), due to the formation of the azonium ion. [source]

A New Class of Cationic Organoiron Polynorbornenes Containing Azo Dyes,

Alaa S. Abd-El-Aziz
Abstract Ring-opening metathesis polymerization of novel organoiron norbornene monomers functionalized with azobenzene chromophores using the Grubbs catalyst resulted in the production of the corresponding cationic organoiron polynorbornenes. UV-vis analysis of the organometallic polymers in DMF showed maxima from 420,430 nm, and upon acidification a bathochromic shift to 510,520 nm was observed. Cyclic voltammetric studies showed that the iron centers underwent reversible reduction steps between ,1.2 and ,1.4 V. Thermogravimetric analysis of the organoiron polymers showed two weight loss steps from 225 to 255,°C and from 400 to 510,°C. Differential scanning calorimetry showed that the cationic organoiron polynorbornenes had glass transition temperatures (Tg) between 145 and 178,°C, while the Tg values of their organic analogs occurred between 99 and 104,°C. [source]

Structural Effects on the Electronic Absorption Properties of 5,6-Dihydroxyindole Oligomers: The Potential of an Integrated Experimental and DFT Approach to Model Eumelanin Optical Properties,

Marco D'Ischia
Elucidation of the relationships between structural features and UV,visible absorption properties of 5,6-dihydroxyindole oligomers is an essential step towards an understanding of the unique optical properties of eumelanins. Herein, we report the first combined experimental and density functional theory (DFT) investigation of the 5,6-dihydroxyindole oligomers so far isolated. 2,2,-Biindolyl 2 and the 2,4,-biindolyl 3 absorb at longer wavelengths relative to 2,7,-biindolyl 4 and their spectra were well predicted by DFT analysis. The absorption bands of 2,4,:2,,4,,- and 2,4,:2,,7,,-triindolyls 5 and 6 also fall at different wavelengths and can be interpreted by DFT simulations as being due to a combination of two main separate transitions. Tetramer 7, in which two 2,4,-biindolyl units are linked through a 2,3,-connection, exhibits a broad chromophore extending over the entire UV range without well defined absorption maxima. Within the dimer,tetramer range examined, three key points emerge: (1) an increase in oligomer chain length does not result in any regular and predictable bathochromic shift; (2) a marked broadening of the absorption bands occurs when going from the monomer to the tetramer structure; and (3) the mode of coupling of the indole units is a crucial, hitherto unrecognized, structural parameter affecting the electronic absorption properties of 5,6-dihydroxyindole oligomers. It is concluded that use of experimentally characterized oligomeric scaffolds as a basis for DFT calculations is a most promising approach to building reliable structural models for studies of eumelanins optical properties. [source]

Comparison of Nonmetal and Metal Hydrophilic Photosensitizer, ATX-S10 (Na) and ATN-2, Binding with Human Serum Proteins Using Spectrophotometry,

M. Yamaguchi
ABSTRACT Intermolecular interactions of human serum proteins with a hydrophilic nonmetalloporphyrin, 13,17-bis(1-carboxy-propionyl)carbomoylethyl-8-ethenyl-2-hydroxy-3-hydroxy-iminoethylidene-2,7,12,18-tetramethylporphyrin sodium salt (ATX-S10 (Na)), or a hydrophilic gallium-metalloporphyrin, diethylenetriamine pentaacetic acid ester of 2-[1-(2-hydroxyethoxy)ethyl]-4-vinyl-deuteroporphyrin (IX) Ga complex (ATN-2), were investigated using spectrophotometry. ATX-S10 (Na) caused a bathochromic shift with albumin, high-density lipoprotein and low-density lipoprotein, but little or no shift was observed with hemopexin, transferrin and immuno-globulin G. In contrast, ATN-2 displayed a bathochromic shift only with hemopexin. These results suggest that the association energy of ATX-S10 (Na) with albumin might be slightly greater than that with lipoproteins and that of ATN-2 with hemopexin might be greater than that with other serum proteins. [source]

,-Crustacyanin, the blue,purple carotenoprotein of lobster carapace: consideration of the bathochromic shift of the protein-bound astaxanthin

P. F. Zagalsky
The crystal structure of a ,-crustacyanin allows an analysis of the various proposals for the mechanism of the bathochromic shift from orange to purple,blue of astaxanthin in this lobster carotenoprotein. Structural and previous chemical and biophysical studies suggest that extension of conjugation by coplanarization of the ,-­ionone rings with the polyene chain and polarization resulting from hydrogen bonding at the C(4) and C(4,) keto groups may be mainly responsible for the bathochromic shift. Additional contributions may arise from medium effects and possibly from bowing of the polyene chain on binding. Previous biophysical data revealing a somewhat symmetrical polarization of astaxanthin in crustacyanin are thereby also accounted for. A puzzling feature remains unexplained: the bathochromic shifts, larger than that of astaxanthin, shown by some cyclopentenedione carotenoids in reconstituted carotenoproteins. This mini review enlarges on the original analysis and conclusions of Cianci et al. [(2002), Proc. Natl Acad. Sci. USA, 99, 9795,9800]. [source]

Tetrahedral Oligothiophenes; Synthesis, X-ray Analysis, and Optoelectronic Properties of Highly Symmetrical, 3D-Branched Oligothiophenes

Kouzou Matsumoto Dr.
Abstract Tetrakis(bithienyl)methane and tetrakis(terthienyl)methane have been synthesized from tetrakis(2-thienyl)methane by use of Suzuki,Miyaura coupling as a key reaction. Their trimethylsilyl (TMS) derivatives are also synthesized. X-ray analysis reveals that each oligothiophene moiety tends to adopt anti -conformations and show relatively small torsion angles between the adjacent thiophene rings. While the longest absorption maxima of these tetrakis(oligothienyl)methanes exhibit only a slight bathochromic shift compared to the corresponding linear oligothiophene derivative, tetrakis(bithienyl)methane and its TMS derivative exhibit an appreciable red-shift in their fluorescence spectra. The intramolecular interaction between thienyl groups of tetrakis(2-thienyl)methane is supported by DFT calculation. [source]

Synthesis of Oligo(thienylfuran)s with Thiophene Rings at Both Ends and Their Structural, Electronic, and Field-Effect Properties

Yasuo Miyata Dr.
Abstract Oligo(thienylfuran)s with thiophene rings at both ends (SOSOSOS, DE-SOSOS, DH-SOSOS, DE-SOSOSOS, and DH-SOSOSOS; S and O denote thiophene and furan rings, respectively, DE and DH denote diethyl- and dihexyl-substituted, respectively) were newly synthesized by repetitive Stille coupling reactions. The UV/Vis maximum absorptions of the oligomers, SO, SOSO, SOSOS, SOSOSO, and SOSOSOS, exhibited a clear bathochromic shift with increasing number of heterocycles. The value of the oxidation peak potential (Epa1) determined by cyclic voltammetry decreased with an increase in the number of heterocycles by 0.06,0.08,V per heterocycle. The crystal-packing structures of DE-SOSOS and DH-SOSOS determined by X-ray crystallography have a herringbone motif and are denser than the reported structures of pentacene and ,-sexithiophene. The morphologies of thin films prepared by vacuum deposition and spin coating were investigated by atomic force microscopy and X-ray diffraction. Among these films, those of DE-SOSOS and DH-SOSOS exhibited highly ordered arrangements. The devices based on vacuum-deposited and spin-coated films of DE-SOSOS and DH-SOSOS displayed the highest FET mobilities of 10,2,10,3,cm2,V,1,s,1 among the oligomers reported in this study. [source]

Theoretical and Experimental Study of the Adsorption of Neutral Glycine on Silica from the Gas Phase

CHEMPHYSCHEM, Issue 6 2005
C. Lomenech Dr.
Abstract The adsorption of neutral glycine onto amorphous silica was investigated both theoretically and experimentally. DFT calculations were performed at the BLYP-631++G** level using a cluster approach. Several possible configurations involving the formation of H bonds between glycine and one, two, or three silanol groups (SiOH) were considered. The most favorable bonding of glycine with one silanol group (45 kJ,mol,1) occurs through the COOH moiety, thus forming a cycle in which the CO group is an H-bond acceptor whereas the acidic OH group is an H-bond donor. With two or three silanol groups, additional H bonds are formed between the amine moiety and the silanol groups, which leads to an increased adsorption energy (70 and 80 kJ,mol,1for two and three silanol groups, respectively). Calculated ,CO, ,HNH, and ,HCHvalues are sensitive to the adsorption mode. A bathochromic shift of ,COas compared to the ,COof free glycine (calculated in the 1755,1790 cm,1range) is found for glycine in interaction with silanol(s). The more H bonds are formed between the COOH moiety and silanol groups, the higher the bathochromic shift. For ,HNH, no shift is found for glycine adsorbed on one and two silanol groups (where the amine is either not bound or an H-bond donor), whereas a bathochromic shift is calculated with three silanols when the amine moiety is an H-bond acceptor. Experimental FTIR spectra performed at room temperature for glycine adsorbed at 160,°C on Aerosil amorphous silica exhibit bands at 1371, 1423, 1630, and 1699 cm,1. The experimental/calculated frequencies have their best correspondence for glycine adsorbed on two silanol groups. It is important to note that the forms giving the best correspondence to experimental frequencies are the most stable ones. [source]

Novel ,-Conjugated Poly(Schiff base) Containing Thiazole and Tetrathiatetrahydropentalene Moieties

Jiang Li-Ming
Abstract A new kind of ,-conjugated heterocyclic poly(Schiff base) was firstly prepared by the condensation reaction between tetrathiatetrahydropentalene-type diketone and bithiazole-diamine in good yields. The polymers were characterized by VPO, FTIR and 1H NMR spectroscopy. A large bathochromic shift was observed in UV-Vis spectra for these polymers due to the ,-,* transition in the conjugated main chain. Brief examination indicated that the nitrogen- and sulfur-containing polymers exhibited an excellent chelating tendency to metal ions and the corresponding polymeric complexes would be expected to have potential in applications. [source]

Dimeric 2,2,-Bipyridylruthenium(II) Complexes Containing 2,2,-Bis(1,2,4-triazin-3-yl)-4,4,-bipyridine-Like Bridging Ligands: Syntheses, Characterization and DNA Binding

Cai-Wu Jiang
Abstract Three new bridging ligands 2,2,-bis(1,2,4-triazin-3-yl)-4,4,-bipyridine (btb), 2,2,-bis(1,2,4-triazino[5,6-f]acenaphthylen-3-yl)-4,4,-bipyridine (btapb), 2,2,-bis(5,6-diphenyl-1,2,4-triazin-3-yl)-4,4,-bipyridine (bdptb) and their dimeric 2,2,-bipyridylruthenium(II) complexes [Ru(bpy)2(btb)Ru(bpy)2]4+ (1), [Ru(bpy)2(btapb)Ru(bpy)2]4+ (2), [Ru(bpy)2(bdptb)Ru(bpy)2]4+ (3) have been synthesized and characterized by elemental analysis, fast atom bombardment (FAB) mass spectrometry or electrospray mass spectrometry (ES-MS), 1H NMR and UV/Visible spectroscopy. The binding behavior of these dimeric complexes with calf thymus DNA (CT-DNA) was investigated by electronic absorption spectroscopy, viscosity measurements, and equilibrium dialysis experiments. The hypochromism of the metal-ligand charge transfer (MLCT) band in the electronic absorption spectra of the dinuclear complexes 1, 2, and 3 is 8.7%, 19% and 33%, respectively, with bathochromic shifts of 5, 5 and 14 nm, respectively. The binding constants are 7.5×104M,1, 4.8×105M,1 and 7.6×105M,1, respectively. Increasing the size of the plane of the bridging ligand increases the hydrophobicity of their complexes, leading to stronger binding by the complexes to calf thymus DNA. The effect of increasing concentrations of these novel dimeric ruthenium(II) complexes on the relative viscosities of CT-DNA is less notable than that of well-known intercalators such as [Ru(bpy)2(dppz)]2+. The equilibrium experiments showed that ,,,3 binding is stronger than ,,,3 binding to CT-DNA. This is the first example of a dinuclear complex binding enantioselectively to CT-DNA measured by equilibrium dialysis. The experiments suggest that the three complexes may be DNA groove binders. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source]

A convenient route to synthesize 1,2,4-triazolo[1,5- a]pyrimidine derivatives and their one and two-photon absorption spectral properties

Hongli Wang
A convenient method for synthesizing ,-(1,2,4-triazolo[1,5- a]pyrimidine-2-sulfonyl)methane derivatives, 3 and 4, by the well known Knoevenagel reaction, in one step, is described. The two chromophores are stilbene-type chromophores containing the same D-,-A structures and end-capped with aromatic group as their donors. Measured with femtosecond multipass Ti:sapphire amplifier as irradiation source (pumped by the laser at 800 nm), the two chromophores show efficient two-photon induced orange red fluorescence emission. The experimental results indicate that the numbers of branches of the two chromophores affect their one-photon properties and two-photon up-conversion emission behaviors, and with the increasing numbers of branches, their wavelengths of ,absmax, ,spfmax and ,tpfmax exhibit bathochromic shifts. [source]

Synthesis of highly luminescent organoboron polymers connected by bifunctional 8-aminoquinolate linkers

Yuichiro Tokoro
Abstract New organoboron aminoquinolate-based polymers linked by ,-conjugated bridge were prepared by Sonogashira,Hagihara coupling of organoboron aminoquinolate-based bisiodo monomers bearing biphenyl or bithiophene moiety with 1,4-diethynylbenzene derivatives. Tetracoordination states of boron atoms in the obtained polymers were confirmed by 11B NMR spectroscopy, and they were also characterized by 1H NMR and IR spectroscopies and size-exclusion chromatography. Their optical properties were studied by UV,vis absorption and photoluminescence spectroscopies. In the region above 400 nm, the polymers prepared from 1,4-diethynyl-2,5-dioctyloxybenzene showed bathochromic shifts when compared with those prepared from 1.4-diethynyl-2-perfluorooctyl-5-trifluoromethylbenzene. The polymers with biphenyl moiety showed higher absolute fluorescence quantum yields (,F = 0.28 and 0.65), whereas those with bithiophene moiety led to decreasing of the low quantum yields (,F = 0.19 and 0.00). The density-functional theory (DFT) and time-dependent,DFT calculations of model compounds corresponding to the polymers were in good agreement with the results from UV,vis properties. The calculations revealed that the electronic structure of the polymer with bithiophene moiety is different from that with biphenyl moiety, and predicted the electron transfer from the bithiophene moiety to the ,-extended quinoline moiety in transition state. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3693,3701, 2010 [source]

,-Crustacyanin, the blue,purple carotenoprotein of lobster carapace: consideration of the bathochromic shift of the protein-bound astaxanthin

P. F. Zagalsky
The crystal structure of a ,-crustacyanin allows an analysis of the various proposals for the mechanism of the bathochromic shift from orange to purple,blue of astaxanthin in this lobster carotenoprotein. Structural and previous chemical and biophysical studies suggest that extension of conjugation by coplanarization of the ,-­ionone rings with the polyene chain and polarization resulting from hydrogen bonding at the C(4) and C(4,) keto groups may be mainly responsible for the bathochromic shift. Additional contributions may arise from medium effects and possibly from bowing of the polyene chain on binding. Previous biophysical data revealing a somewhat symmetrical polarization of astaxanthin in crustacyanin are thereby also accounted for. A puzzling feature remains unexplained: the bathochromic shifts, larger than that of astaxanthin, shown by some cyclopentenedione carotenoids in reconstituted carotenoproteins. This mini review enlarges on the original analysis and conclusions of Cianci et al. [(2002), Proc. Natl Acad. Sci. USA, 99, 9795,9800]. [source]

Highly Fluorescent Conjugated Pyrenes in Nucleic Acid Probes: (Phenylethynyl)pyrenecarbonyl-Functionalized Locked Nucleic Acids

Abstract In recent years, fluorescently labeled oligonucleotides have become a widely used tool in diagnostics, DNA sequencing, and nanotechnology. The recently developed (phenylethynyl)pyrenes are attractive dyes for nucleic acid labeling, with the advantages of long-wave emission relative to the parent pyrene, high fluorescence quantum yields, and the ability to form excimers. Herein, the synthesis of six (phenylethynyl)pyrene-functionalized locked nucleic acid (LNA) monomers M1,M6 and their incorporation into DNA oligomers is described. Multilabeled duplexes display higher thermal stabilities than singly modified analogues. An increase in the number of phenylethynyl substituents attached to the pyrene results in decreased binding affinity towards complementary DNA and RNA and remarkable bathochromic shifts of absorption/emission maxima relative to the parent pyrene fluorochrome. This bathochromic shift leads to the bright fluorescence colors of the probes, which differ drastically from the blue emission of unsubstituted pyrene. The formation of intra- and interstrand excimers was observed for duplexes that have monomers M1,M6 in both complementary strands and in numerous single-stranded probes. If more phenylethynyl groups are inserted, the detected excimer signals become more intense. In addition, (phenylethynyl)pyrenecarbonyl,LNA monomers M4, M5, and M6 proved highly useful for the detection of single mismatches in DNA/RNA targets. [source]

Effect of Core Twisting on Self-Assembly and Optical Properties of Perylene Bisimide Dyes in Solution and Columnar Liquid Crystalline Phases

Zhijian Chen
Abstract A series of highly soluble and fluorescent core-twisted perylene bisimide dyes (PBIs) 3,a,f with different substituents at the bay area (1,6,7,12 positions of the perylene core) were synthesized and fully characterized by 1H,NMR, UV/Vis spectroscopy, MS spectrometry, and elemental analysis. The ,,, aggregation properties of these new functional dyes were investigated in detail both in solution and in condensed phase by UV/Vis and fluorescence spectroscopy, vapor pressure osmometry (VPO), differential scanning calorimetry (DSC), polarizing optical microscopy (POM), and X-ray diffraction. Concentration-dependent UV/Vis measurements and VPO analysis revealed that these core-twisted ,-conjugated systems show distinct self-dimerization equilibria in apolar solvent methylcyclohexane (MCH) with dimerization constants between 1.3×104 and 30,M,1. The photoluminescence spectra of the dimers of PBIs 3,a,f exhibit bathochromic shifts of quite different magnitude which could be attributed to different longitudinal or rotational offsets between the dyes as well as differences in the respective ,,, stacking distance. In condensed state, quite a few of these PBIs form luminescent rectangular or hexagonal columnar liquid crystalline phases with low isotropization temperatures. The effects of the distortion of the , systems on their ,,, stacking and the optical properties of the resultant stacks in solution and in LC phases have been explored in detail. In one case (3,a) a particularly interesting phase change from crystalline into liquid crystalline could be observed upon annealing that was accompanied by a transformation from non-fluorescent H -type into strongly fluorescent J -type packing of the dyes. [source]