Interaction Of Chromophores Research Articles

Influence of interaction of chromophores, linked by the unconjugated chain, on the luminescence properties of biscyanine dyes

Deactivation of electronically excited state of chemically bound dimers – biscyanines with two chromophores linked by unconjugated chains and corresponding monomer dye was investigated. It was found that the quantum yield of dimer fluorescence is lower than that of a monomer dye. The amount of quantum yield of fluorescence decreases with the increase of chromophores interaction degree (the decrease of the isolating polymethylene bridge length). It is shown on the basis of the external heavy-atom effect studies that the decrease of biscyanines fluorescence ability is connected with the enhancment of singlet–triplet intersystem crossing ( S 1⤳ T 1 ). It has been established that the probability of the triplet states population in biscyanines with chromophores in parallel arrangement is considerably higher than that in similar compounds with an angular arrangement of chromophores. The delayed fluorescence was observed in the case of dyes with parallel arrangment of chromophores.

EFFECT OF THE ELECTROSTATIC INTERACTIONS OF CHROMOPHORES ON THE MACROSCOPIC SECOND-ORDER NONLINEAR OPTICAL PROPERTIES OF THE POLYMER FILMS

The polyetherketone (PEK-c) guest-host system thin films doped with 3-(1,1-dicyanothenyl)-1-phenyl-4,5-dihydro-1H-pryazole (DCNP) were prepared. Their second-order nonlinear optical (NLO) coefficients χ33(2) were measured by using Maker fringe method for the polymer films doped with different weight percents of DCNP. Experimental results indicate that the second-order NLO properties of the poled polymer films could decrease with the chromophore loading increasing when the chromophore loading reaches a fairly high level. In this paper, the relationship between the macroscopic second-order NLO coefficient and the chromophore number density was modified under considering the role of the electrostatic interactions of chromophores in the polymer film. According to the modified relationship, the macroscopic second-order NLO coefficient is no longer in direct proportion with the chromophore number density in the polymer film. The effect of the electrostatic interactions of chromophores on second-order NLO properties was discussed. The attenuation of the macroscopic second-order NLO activity can be demonstrated by the role of the chromophore electrostatic interactions at high loading of chromophore in the polymer systems.

Effects of chromophore interaction in photophysics and photochemistry of cyanine dyes

Spectral and fluorescent properties of ketocyanine dyes (polyenic bis‐ω, ω′‐aminoketones) and cation‐anionic polymethine dyes of various structures were studied. The symmetric ketocyanines were shown to have a long‐wavelength absorption band bathochromically shifted in comparison with that of the asymmetric ketocyanines with the same total length of the polyenic chain. The nonlinear ketocyanines exhibit the additional short‐wavelength band in their absorption spectra, which can be more intense than the longwavelength band. The absorption spectra of ion pairs of cation‐anionic dyes with overlapping cation and anion bands contain a new intense short‐wavelength band inactive in fluorescence excitation. These spectral peculiarities are explained on the basis of chromophore interaction model. It has also been shown that the T1 levels of ketocyanine chromophores do not essentially interact with each other in a ketocyanine molecule in nonpolar solvents; in polar solvents this interaction becomes appreciable due to lowering the potential barrier for conjugation.

Compression of the dye monolayer at the air/water interface studied by second harmonic generation

The second harmonic (SH) generation efficiency upon compression of insoluble rhodamine C18 and fluorescein O322 monolayers at the air/water interface has been measured. The SH intensity dependence on area per molecule clearly varied for four main regions: expanded monolayer, expanded–condensed transition region, condensed monolayer and collapse point. This SH intensity dependence was similar with the π–A isotherm for both molecules. The SH intensity change would be explained with a model of interactions of dye chromophores based on the dipole–dipole correlation, CH-π interaction, aggregates of electronic transition moments and formation of large order π-conjugated system.

Bisimidazoacridones: Effect of Molecular Environment on Conformation and Photophysical Properties

Bisimidazoacridones (BIA) are highly selective antineoplastic and antiviral agents. Ultraviolet-visible spectroscopy and steady-state and time-resolved fluorescence spectroscopy studies were carried out to probe the behavior of BIA in aqueous and nonaqueous (organic solvents, colloid micelles) solutions. Three ranges of fluorescence lifetimes were revealed: approximately 0.2-0.5 ns (presumably reflecting the chromophore-chromophore interaction), approximately 1-5 ns (interpreted as linker-perturbed chromophore decay) and approximately 6-12 ns (nonperturbed chromophore decay). The pre-exponential and steady-state contributions of these components to the decay signal as well as the data on steady-state fluorescence intensities, wavelength maxima and bandwidths showed that the BIA conformations in solution were sensitive to the environment and influenced strongly by their propensity to minimize hydrophobic interactions. In water, the molecules tend to adopt condensed conformations that bring the two imidazoacridone moieties into close proximity (resulting in intramolecular fluorescence energy transfer), while in nonaqueous systems the conformations become more relaxed. The transfer from a polar to more lipophilic environment of macromolecules is suggested to be the main driving force for binding of BIA to biomacromolecules, such as nucleic acids.

Contribution of Methyls in Retinal Side Chain to Regioselective Photoisomerization of Retinochromes

Abstract All-trans-9-demethyl-11-methylretinal was synthesized to elucidate the chromophoric interaction between hydrophobic part in retinochrome and 9-methyl substituent of retinal. Photoirradiation of its pigment efficiently gave the 11-cis-isomer in 90% regioselectivity, whereas that of 9-demethylretinochrome provided the 11-cis isomer in 49% selectivity. Structural contribution to regiospecific photoisomerization was proved, in comparison with the other retinochrome analogues, that 9- or 11-methyl substituent is a requisite for highly regioselective photoisomerization, but 13-methyl group is not.

Effect of anion binding on iodopsin studied by low-temperature fourier transform infrared spectroscopy.

The effect of anion binding on iodopsin, the chicken red-sensitive cone visual pigment, was studied by measurements of the Fourier transform infrared spectra of chloride- and nitrate-bound forms of iodopsin at 77 K. In addition to the blue shift of the absorption maximum upon substituting nitrate for chloride, the C=C stretching vibrations of iodopsin and its photoproducts were upshifted 5-6 cm(-)(1). The C=NH and C=ND stretching vibrations were the same in wavenumber between the chloride- and nitrate-bound forms, indicating that the binding of either chloride or nitrate has no effect on the interaction between the protonated Schiff base and the counterion. The vibrational bands of iodopsin in the fingerprint and the hydrogen out-of-plane wagging regions were insensitive to anion substitution, suggesting that local chromophore interactions with the anions are not crucial for the absorption spectral shift. In contrast, bathoiodopsin in the chloride-bound form exhibited an intense C(14)H wagging mode, whose intensity was considerably weakened upon substitution of nitrate for chloride. These results suggest that binding of chloride changes the environment near the C(14) position of the chromophore, which could be one of the factors in the thermal reverse reaction of bathoiodopsin to iodopsin in the chloride-bound form.

Self‐assembled multilayers of photochromic bola‐amphiphile and ionene‐type oligomer: Relation of aggregate state and photoisomerization

AbstractPhotoisomerization process of azobenzene has been studied in the multilayer assemblies of poly(vinylsulfate, potassium salt) and two different layer‐elements; 4,4′‐azobenzene‐bis(12‐trimethylammonium‐N‐yl dodecyloxy) dibromide (BA‐12, 1) and an ionene oligomer, poly(4,4′‐azobenzene‐bis(12‐dimethyl‐ammonium‐N‐yl dodecyloxy) bromide) (PAZ‐12, 2). The change of the photoactive layers from BA‐12 to PAZ‐12 was found to dramatically influence the photoisomerization characteristics of the azobenzene in the multilayer. Surprisingly, we have observed that the chromophore interaction in PAZ‐12 is stronger than that in BA‐12 in self‐assembled (SA) film (λmax = 320 nm compared to 341 nm), although the aggregate formation is considered to be hindered by the strains of the polymer chains. For BA‐12/PVS and PAZ‐12/PVS multilayers, the steady state between cis and trans isomers reached after ca 20 min. and 48 min. of UV irradiation, respectively. It was also found that after first one trans‐cis‐trans cycle of the photoisomerization, the trans to cis isomerization was completed in 30 sec of irradiation in the following 10 cycles without appearance of any fatigue in the multilayer film.

Vibrational Spectrum and Torsional Potential of 2-Methoxy-3-methyl-1,4-benzoquinone

Stable conformations and vibrational spectra of 2-methoxy-3-methyl-1,4-benzoquinone were calculated using density functional methods. Two stable conformers have been found which differ in their vibrational spectrum. Although the calculated infrared spectra of the two conformers differ with respect to several modes, a definite assignment of the experimentally available bands to one of the two conformers is difficult. Protein−chromophore interactions have been studied by modeling quinone−H2O, quinone−Li+, and quinone−N complexes. A complexation with water already considerably affects the relative energies of the two conformers and the torsional barrier for the rotation of the methyl part of the methoxy group. In fully optimized quinone−water complexes, vibrational modes in the CO and CC stretching mode region are affected through the complexation. Complexation with a positively charged counter ion dramatically changes the energetics of the system and changes the former minimum energy conformation into a saddle point. Vibrational frequencies are more strongly affected than upon complexation with a water molecule.

Second-harmonic generation of biological interfaces: probing the membrane protein bacteriorhodopsin and imaging membrane potential around GFP molecules at specific sites in neuronal cells of C. elegans

Second-harmonic generation (SHG) is applied to problems of probing membrane proteins and functionally imaging around selective sites and at single molecules in biological membranes. The membrane protein bacteriorhodopsin (bR) has been shown to have large second-harmonic (SH) intensities that are modulated by protein/retinylidene chromophore interactions. The nonlinear optical properties of model compounds, which simulate these protein chromophore interactions in retinal proteins, are studied in this work by surface SHG and by hyper-Rayleigh scattering. Our results indicate that non-conjugated charges and hydrogen bonding effects have a large effect on the molecular hyperpolarizability of the retinal chromophore. However, mbR, the model system studies suggest that polarizable amino acids strongly affect the vertically excited state of the retinylidene chromophore and appear to play the major role in the observed protein enhancement (>50%) of the retinylidene chromophore molecular hyperpolarizability and associated induced dipole. Furthermore, the data provide insights on emulating these interactions for the design of organic nonlinear optical materials. Our studies have also led to the development of dyes with large SH intensities that can be embedded in cell membranes and can functionally image membrane potential. Single molecules of such dyes in selected single molecular regions of a cell membrane have been detected. SHG from green fluorescent protein (GFP) selectively expressed in concert with a specific protein in neuronal cells in a transgenic form of the worm C. elegans is also reported. The membrane potential around the GFP molecules expressed in these cells has been imaged with SHG in live animals.

Synthesis and photonics of ketocyanine dyes, 2,6-bis(4-dimethylaminoalka-1,3-dienyl)-4H-pyran-4-ones and ethoxytridecamethine salts based on them

The reactions of β-dimethylaminoacrolein aminals with 2,6-dimethyl-γ-pyrone lead to 2,6-bis(4-dimethylaminoalka-1,3-dienyl)-4H-pyran-4-ones, whose alkylation affords ethoxytridecamethine salts. The spectral and fluorescence properties of the synthesized compounds were studied. Their absorption spectra are unusual; along with the long-wavelength band in the visible spectral region, they contain a much more intense short-wavelength band in the near UV region. This pattern of the absorption spectra is explained in terms of the model of chromophore interaction, assuming an acute angle between the chromophore “halves” of the polyene chain of the dye molecule. The central pyran ring in the ethoxytridecamethine salts can hamper conjugation in the polymethine chain. Thermochromism of 2,6-bis(4-dimethylaminoalka-1,3-dienyl)-4H-pyran-4-ones (the long-wavelength shift of the absorption spectra on cooling of the solutions) is observed; only the long-wavelength absorption band undergoes a pronounced thermochromic shift. The introduction of methyl or phenyl substituents into the polyene chains of substituted 4H-pyranones decreases the fluorescence quantum yield.

Fluorescence quenching by intermolecular π– π interactions of 2,5-bis( N,N-dialkylamino)-3,6-dicyanopyrazines

The fluorescence properties of 2,5-bis( N,N-dialkylamino)-3,6-dicyanopyrazine dyes in the solid state were correlated with their molecular stacking behavior. The optimized molecular structures were evaluated by using MOPAC PM3 and AM1 methods and their stacking behaviors of the π-chromophoric system were simulated from their three dimensional molecular structures and 1H NMR spectra. The steric requirements of the substituents in the parent chromophoric system were the main cause of the spectral changes in the absorption and fluorescence maxima and fluorescence intensity in the solid state. Intermolecular π–π interactions effectively quenched the solid state fluorescence and, consequently, the degree of fluorescence quenching can be used as an indicator of intermolecular π–π interactions of fluorescence dyes chromophores. ©

Palladium Porphyrin Containing Zirconium Phosphonate Langmuir−Blodgett Films

The substituted tetraphenylporphyrins palladium 5,10,15,20-tetrakis(2‘,3‘,5‘,6‘-tetrafluorophenyl-4‘-octadecyloxyphosphonic acid)porphyrin (16) and palladium 5,10,15-tris(2‘,6‘-dichlorophenyl)-20-(2‘,3‘,5‘,6‘-tetrafluorophenyl-4‘-octadecyloxyphosphonic acid)porphyrin (17) have been studied as Langmuir monolayers and as zirconium phosphonate Langmuir−Blodgett (LB) films. Using a three-step deposition technique, symmetric and alternating zirconium phosphonate bilayers and multilayers were prepared. In these films, the porphyrin constituent resides in the hydrophobic region of the monolayer and the phosphonate substituents bind zirconium ions in the hydrophilic part. Films of the pure porphyrins and of mixtures with octadecylphosphonic acid (OPA) were prepared. Langmuir monolayers were characterized with pressure vs area isotherms and reflectance UV−vis spectroscopy. LB films were studied with transmittance UV−vis and X-ray diffraction. Control over chromophore interaction was achieved by chemical modificati...

Bisimidazoacridones: Effect of Molecular Environment on Conformation and Photophysical Properties

Bisimidazoacridones (BIA) are highly selective antineoplastic and antiviral agents. Ultraviolet-visible spectroscopy and steady-state and time-resolved fluorescence spectroscopy studies were carried out to probe the behavior of BIA in aqueous and nonaqueous (organic solvents, colloid micelles) solutions. Three ranges of fluorescence lifetimes were revealed: ˜0.2-0.5 ns (presumably reflecting the chromophore–chromophore interaction), ˜1–5 ns (interpreted as linker-perturbed chromophore decay) and ˜6–12 ns (nonperturbed chromophore decay). The pre-exponential and steady-state contributions of these components to the decay signal as well as the data on steady-state fluorescence intensities, wavelength maxima and bandwidths showed that the BIA conformations in solution were sensitive to the environment and influenced strongly by their propensity to minimize hydrophobic interactions. In water, the molecules tend to adopt condensed conformations that bring the two imi-dazoacridone moieties into close proximity (resulting in intramolecular fluorescence energy transfer), while in nonaqueous systems the conformations become more relaxed. The transfer from a polar to more lipophilic environment of macromolecules is suggested to be the main driving force for binding of BIA to biomacromolecules, such as nucleic acids.

Investigation of spectral diffusion in PMMA on timescales from 10 −5 to 10 4 seconds via transient and photophysical hole burning

Spectral diffusion (SD) in PMMA samples, doped with Zn-tetrabenzoporphine, was investigated via triplet state populational hole burning in the absorption spectrum of a chromophore on a timescale from 20 μs to 200 ms and via photophysical persistent hole burning on a timescale from 10 to 10 4 s covering the temperature interval 1.7–10 K. The SD rates on microsecond and on long timescales ( t>10 s) coincide. An anomalous increase of the SD rate was found in the millisecond range which cannot be attributed to peculiarities in the relaxation rate distribution of the two-level systems in PMMA. The apparent correlation of the observed anomalous SD region with the time domain of the deactivation of the chromophore's triplet state points to other broadening mechanisms connected with triplet state dynamics or photophysical hole burning. We perform a careful analysis of the possible influence of such mechanisms on transient hole broadening. We show that the complete experimental data cannot be explained by mechanisms like chromophore–chromophore interaction, background persistent hole burning, etc. The nature of the discovered anomaly remains unclear.

Photoinduced Orientation of Azobenzene Chromophores in Amorphous Polymers As Studied by Real-Time Visible and FTIR Spectroscopies

In situ dynamical study of the photoinduced orientation of the DR1 azobenzene derivative in a doped PMMA matrix and in p(DR1A-co-MMA) copolymers was carried out using real-time visible and infrared spectroscopies. The different mechanisms occurring during the photoisomerization cycles were highlighted by following the time dependence of the normalized average absorbance (T0), the normalized linear dichroism (T2) and the order parameter (P2) during the orientation (laser on) and the relaxation (laser off) periods. The thermal cis−trans back-relaxation and the angular redistribution were followed separately from the T0 and T2 relaxation curves, respectively. The orientation and relaxation curves were fitted by the Kohlrausch−Williams−Watts (KWW) function in order to compare the rate constant and the distribution width for various samples. On one hand, the chromophore−matrix interactions were investigated in doped systems by changing the tacticity of the PMMA matrix. On the other hand, the chromophore−chromophore interactions in functionalized polymers were studied by changing the concentration of azobenzene units in copolymer systems.

Physicochemical aspects of the creation of modern light-sensitive materials based on polymethine dyes

Features of the photophysical and photochemical characteristics of polymethine dyes that determine their use as light-sensitive materials (luminescent light concentrators, fluorescent probes and markers for the intercalation of DNA, laser media, polymerization photoinitiators, electroluminescent media) are analyzed. The main paths of the degradation of the electronic excitation energy (photoisomerization, intercombination and internal conversion, electron phototransfer in ion pairs, interaction of chromophores, like and mixed association) are discussed. The relation between these factors and the structure of the dyes and the nature of the medium is examined. Special attention is paid to methods of creating and optimizing colored light-sensitive polymeric materials.

Optically Induced Dichroism and Birefringence of Disperse Red 1 in Hybrid Polymers

We report results of dichroism and birefringence measurements on Disperse Red 1 (DR1) in hybrid polymers. To investigate the influence of the matrix−chromophore interaction, we employ doped and functionalized systems using three kinds of matrices with different rigidity. Writing, erasing, and rewriting processes are performed on the polymer films at temperatures ranging from 50 to 300 K. Two processes are recognized, the photochemical cis−trans isomerization of the dye molecules and a thermal motion of the photoactive chromophore inside the surrounding matrix. By comparing results obtained from the different network systems, we find that the main parameter correlated with the extent of induced anisotropy is the degree of mobility of the chromophore within the surrounding matrix.

Solving challenging bioorganic problems by exciton coupled CD

Abstract

On the importance of including intermolecular correlations in the measurement of polymer interdiffusion by fluorescence nonradiative energy transfer

AbstractThere has been a great deal of recent interest in monitoring polymer interdiffusion with fluorescence nonradiative energy transfer (NRET), a typical experiment consisting of polymer chains labeled with a donor chromophore interdiffusing with chains labeled with an acceptor chromophore, causing an increase in energy transfer efficiency, E. A factor nearly always ignored in models of this process is the fact that chromophore interactions are screened out because of intermolecular correlation effects, leading to a lower E than would otherwise be expected. The model of Dhinojwala and Torkelson (Macromolecules 27, 4817 (1994)) has been modified to include correlations in order to explore the impact that ignoring correlations has on the diffusion coefficients calculated in such experiments. When correlations are included in the model, E is proportional to (Dpt)1/2/x for t<x2/(16Dp) (where x is the thickness of the donor‐labeled film and Dp is the polymer diffusion coefficient), similar to when correlations are ignored. Within this linear regime errors in Dp associated with ignoring correlations are typically less than 20% for logically defined systems, which may be insignificant given the uncertainty with which diffusion coefficients are normally reported. However, this study clearly demonstrates that precautions should be used in all experiments of this type to stay in this linear regime, as improperly accounting for or ignoring correlation effects at longer diffusion times can lead to the spurious result that apparent diffusion coefficients decrease with annealing time, by factors of 2 to 5 to as much as an order of magnitude or more at sufficiently long time. Systems designed to minimize correlation effects should have a large Förster radius and a sufficiently high ratio of acceptors to donors; with such a situation and the use of NRET data from the linear regime of E vs. t1/2, it is possible under many experimental circumstances to determine diffusion coefficients within small error even when the effects of correlations are ignored.