Stilbazolium Merocyanines Research Articles

Effect of substituents on the thermochromism of stilbazolium merocyanines incorporated in epoxy resin

The thermochromic effect (in the range 283–333K) on the spectroscopic properties of stilbazolium merocyanine derivatives are substituted by groups of different donor–acceptor qualities (–H, –C(CH3)3, –NO2 and –OCH3) located in the ortho position to the carbonyl group of the quinonoid ring was examined. The samples were embedded in a polymer matrix from the epoxy resin.Results show that the size of thermochromic effect of stilbazolium merocyanines can be influenced by attaching substituents of different donor–acceptor nature. The smallest value of this effect was recorded for dye substituted by large tert-butyl groups, and the largest for derivative with –NO2 group substituent. The thermosensitvity investigated dyes was dependent on: (1) an equilibrium between quinonoid form and benzenoid form (zwitterion), (2) the polarization of molecules that facilitate the formation of H-type aggregates.

Spectral properties of stilbazolium merocyanines – potential sensitizers in photodynamic therapy and diagnosis: Part II. Merocyanines in resting and stimulated lymphocytes

Three stilbazolium merocyanines, selected on the basis of their investigations in model systems in part I of this work [J. Photochem. Photobiol., A: Chem. 163 (2004) 127], were introduced into resting and phytohemagglutinin-stimulated lymphocytes. All these merocyanines in solution exhibit high yield of generation of very photochemically active triplet states, but are characterized by different yields of fluorescence emission. The PHA-stimulated lymphocytes were the model of tumor cells. The fluorescence emission and fluorescence excitation spectra are more sensitive to small changes in the cell material than absorption spectra. The course of the photodynamic reactions in stained and unstained cells were established.The efficiency of triplet states generation of the dyes incorporated into stimulated cells has been evaluated using time-resolved photothermal spectroscopy. As follows from the photographs of stained cancerous cells taken by means fluorescence microscope, merocyanines are located predominantly in cell membranes. The spectral properties of the dye-sensitizes in solutions and in the cells can differ therefore the selection of proper sensitizers for medical applications made on the ground of the investigation of dye molecules in simple artificial model systems is only preliminary. The selected dyes have to be further investigated after introducing them into resting and PHA-stimulated lymphocytes. It has been shown that the dyes exhibiting high yields of triplet state generation in the stimulated cells usually are also efficient sensitizers of photodynamic reactions. The exceptions are the dyes undergoing fast photobleaching in the cells.

Spectral properties of stilbazolium merocyanines – potential sensitizers in photodynamic therapy and diagnosisPart II. Merocyanines in resting and stimulated lymphocytes

Three stilbazolium merocyanines, selected on the basis of their investigations in model systems in part I of this work [J. Photochem. Photobiol., A: Chem. 163 (2004) 127], were introduced into resting and phytohemagglutinin-stimulated lymphocytes. All these merocyanines in solution exhibit high yield of generation of very photochemically active triplet states, but are characterized by different yields of fluorescence emission. The PHA-stimulated lymphocytes were the model of tumor cells. The fluorescence emission and fluorescence excitation spectra are more sensitive to small changes in the cell material than absorption spectra. The course of the photodynamic reactions in stained and unstained cells were established. The efficiency of triplet states generation of the dyes incorporated into stimulated cells has been evaluated using time-resolved photothermal spectroscopy. As follows from the photographs of stained cancerous cells taken by means fluorescence microscope, merocyanines are located predominantly in cell membranes. The spectral properties of the dye-sensitizes in solutions and in the cells can differ therefore the selection of proper sensitizers for medical applications made on the ground of the investigation of dye molecules in simple artificial model systems is only preliminary. The selected dyes have to be further investigated after introducing them into resting and PHA-stimulated lymphocytes. It has been shown that the dyes exhibiting high yields of triplet state generation in the stimulated cells usually are also efficient sensitizers of photodynamic reactions. The exceptions are the dyes undergoing fast photobleaching in the cells.

Spectral properties of stilbazolium merocyanines – potential sensitizers in photodynamic therapy and diagnosis: Part I. Merocyanines in model systems

Spectral and photochemical properties of seven stilbazolium merocyanines of different chain length and side groups attached, dissolved in ethanol or methanol solutions as well as in polyvinyl alcohol water solutions and films, were investigated. The absorption, fluorescence emission and fluorescence excitation spectra as well as steady state photoacoustic and laser induced optoacoustic spectroscopy signals were measured.Triplet states are, because of their slow decay time, usually very effective in photochemical reaction; therefore dyes with efficient triplet states generation are suitable for destruction of illuminated diseased cells. The laser induced optoacoustic measurements were used to evaluate the efficiency of generation and decay times of dye triplet states. The quenching of the dye triplet state by oxygen was also studied.The results show that properties of merocyanines and their interactions with macromolecules depend strongly on the type of side groups attached. The dyes with NO2 groups attached exhibit low yield of fluorescence therefore they could be useful rather in photodynamic therapy (PDT) than for diagnostic purposes. Some of the merocyanines investigated exhibit high yields of triplet state generation and, therefore, should be effective in photodynamic reactions.Further investigations will be carried out with the same dyes on healthy and diseased cells in order to show whether it is possible, on the grounds of spectral and photochemical properties of dye molecules in simple model systems, to predict the efficiencies of the dye incorporation into cells and the yield of photodynamic reactions.

Spectral properties of stilbazolium merocyanines oriented in stretched polymer films and Langmuir–Blodgett monolayers

Three stilbazolium merocyanines: 1-(6′-hydroxyhexyl)-4-[(4-oxocyclohexa-2,5-dienylidene)ethylidene]-1,4-dihydropyridine; 1-(11′-hydroxyhexyl)-4-[(4-oxocyclohexa-2,5-dienylidene)ethylidene]-1,4-dihydropyridine; 1-(10′-carboxydecyl)-4-[4-oxocyclohexa-2,5-dienylidene)ethylidene]-1,4-dihydropyridine salt HCl located in Langmuir–Blodgett monolayers and deposited on quartz plate as well as embedded in isotropic or stretched polyvinyl alcohol films were investigated. Dyes occur in protonated and free-base forms. The concentration ratio of these forms depends on pH of subphase (for monolayers) or resin addition (in polymer film).The polarized absorption and fluorescence spectra were measured and coefficients of absorption and emission anisotropy were calculated. Dye molecules were in both matrices oriented, but degrees of orientation of various forms of dye were different. The anisotropies of absorption and emission are also different which strongly suggests the occurrence of dye forms with different yield of fluorescence and various orientations. The formation of mixed aggregates of protonated and free-base form is suggested. The orientation of stilbazolium merocyanines in anisotropic matrix is important in the application of these dyes as the sensors for measurements of the local electric field in biological membranes as well as for the formation polarizing absorption polymer film used in some types of two-colours liquid crystal displays.

Action spectra of the photopotential generation for pigment and dye solutions in nematic liquid crystals located in the electrochemical cell

The method of measurements of the action spectra of photopotential generation using a modulated acting light beam was elaborated and applied to two systems: the solutions of stilbazolium merocyanines and to the mixture of chlorophyll a and luteine. Both types of samples were dissolved in nematic liquid crystal and located either between two semiconducting electrodes, or between a transparent gold electrode and a semiconducting electrode. By changing the frequency of light modulation or the phase shift between a modulated light beam and a measured photopotential signal, information about the kinetics of photopotential generation is obtained. The free base and protonated merocyanine forms exhibit different kinetics of potential generation. The amplitude of the photopotential of the chlorophyll and luteine mixture is higher than the sum of the amplitudes of the photopotential of these pigments located in separated cells. In a cell with two semiconducting electrodes, the light gradient (e.g., different illumination of front and back electrodes due to light absorption) plays an important role in photopotential generation.

Incorporation of stilbazolium merocyanines into human leukocytes measured by flow cytometry.

Human peripheral blood leukocytes were incubated with thirteen various merocyanines of the stilbazolium betaine type and the fluorescence intensities of the cells were measured by flow cytometry. The fluorescence intensity of lymphocytes, monocytes and granulocytes depended on the time and temperature of incubation with the dyes. An increase in the incubation temperature enhanced the fluorescence intensity whereas washing of the cells after incubation had little influence on the observed emission. This points to incorporation of the dye molecules into the cell membrane. From the measured fluorescence intensities corrected for relative fluorescence yields, the relative efficiencies of incorporation into the cells of the various merocyanines tested were evaluated. The efficiency was dependent on the type of the cells and the lenght and side groups of the merocyanine molecules studied.

Incorporation of stilbazolium merocyanines into resting and stimulated mononuclear leukocytes.

Stimulated and resting mononuclear leukocytes were incubated with a stilbazolium merocyanine dye 1-(6'-hydroxyhexyl)-4-[(4-oxocyclohexa-2,5- dienylidene)ethylidene]-1,4-dihydropyridine and immobilized in isotropic and stretched polyvinyl alcohol film. Polarized absorption, fluorescence and fluorescence excitation spectra were collected and the anisotropy of absorption and emission were calculated. Analysis of the spectra pointed to: i. the occurrence of perturbation of the membrane structure by incubation with the dye, and ii. influence of the blood serum addition, during the process of incubation with the dye, on the efficiency of incorporation of merocyanine into the cells and the degree of the dye orientation in the membrane. A small fraction of the dye molecules introduced into resting cells was found oriented to a higher degree than a large fraction incorporated into stimulated cells. The incubation time longer than 15 min caused strong changes in the membrane structure both of the resting and stimulated cells.

Electrochemical cell with stilbazolium merocyanines oriented in a nematic liquid crystal

The photovoltaic effect and current—voltage ( I(V)) characteristics of an electrochemical cell, consisting of a layer of merocyanine (1-(6′-hydroxyhexyl)-4-/(3,5-di- tert-butyl-4-oxocyclohexa-2,5-dienylidene)ethylidene/-1,4- dihydropyridine and 1-(11′-hydroxyundecyl)-4-/(3,5-di- tert-butyl-4-oxocyclohexa-2,5-dienylidene)ethylidene/-1,4-dihydropyridine) in a nematic liquid crystal ( p-methoxybenzylidene p′-butylaniline (MBBA) plus p-ethoxybenzylidene p′-butylaniline (EBBA)) sandwiched between two semiconducting (In 2O 3) electrodes and covered with polyimide orienting layers, were investigated. Both dyes are uniaxially oriented as a result of the guest—host effect, but the dye with the longer chain to a lower degree. Both dyes occur in free base and protonated forms. The maximum of the photopotential action spectrum is located in the absorption region of the protonated form of the dye. The first illumination of the cell generates “formation” potentials of opposite sign for the two merocyanines investigated. The difference in sign can be related to several processes, such as the different perturbations of the liquid crystal arrangement (which can produce an additional polarized charge of the matrix) and the different concentrations of free base and protonated forms. The dye located at the illuminated semiconducting electrode (which is responsible for the formation of the surface charge) and the dye molecules dissolved in the bulk volume of the liquid crystal are both responsible for this effect. A sequence of light and dark periods applied to a “formed” cell generates an additional negative potential related to electron tunnelling from the excited dye molecules to the semiconducting electrode. The cells are sensitive to the polarization of the light. All the effects observed can be related to the interaction of the dye molecules with the liquid crystal matrix and to the electric field formed at the junction between the illuminated semiconducting electrode and the pigmented liquid crystal layer.

ChemInform Abstract: Effect of Substituents on the Solvatochromism of Stilbazolium Merocyanines

ChemInformVolume 21, Issue 44 Physical Organic Chemistry ChemInform Abstract: Effect of Substituents on the Solvatochromism of Stilbazolium Merocyanines M. NIEDBALSKA, M. NIEDBALSKA Dep. Chim.-Biol., Univ. Que., Trois-Rivieres, Que., Can. G9A 5H7Search for more papers by this authorI. GRUDA, I. GRUDA Dep. Chim.-Biol., Univ. Que., Trois-Rivieres, Que., Can. G9A 5H7Search for more papers by this author M. NIEDBALSKA, M. NIEDBALSKA Dep. Chim.-Biol., Univ. Que., Trois-Rivieres, Que., Can. G9A 5H7Search for more papers by this authorI. GRUDA, I. GRUDA Dep. Chim.-Biol., Univ. Que., Trois-Rivieres, Que., Can. G9A 5H7Search for more papers by this author First published: October 30, 1990 https://doi.org/10.1002/chin.199044039Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume21, Issue44October 30, 1990 RelatedInformation

Polarized absorption and emission spectra of stilbazolium merocyanines

Natural light and polarized absorption and fluorescence spectra of six stilbazolium merocyanines (with different side groups and molecule lengths) embedded in polyvinyl alcohol film were measured. In a stretched film, dye molecules are highly oriented. Different spectra are obtained for the same dye in isotropic and anisotropic polymer films. Conclusions concerning the degree of dye orientation and the distribution of molecules in the direction of film stretching are made on the basis of different combinations of polarized fluorescence components. Dyes occur in the polymer matrix in protonated and free base forms. The protonation of merocyanines molecules influences their degree of orientation in an anisotropic matrix and the aggregation of the dye. Aggregation of protonated and free base forms competes with the interaction of the dye with the matrix. Aggregates are oriented in a different way from monomers. The side groups attached to the dye chain have a strong influence on the orientation of the molecules and their aggregation properties.

Effect of substituents on the solvatochromism of stilbazolium merocyanines

The visible spectra of a series of merocyanines, derivatives of 4-[(4-oxocyclohexa-2,5-dienylidene)ethylidene]-1,4-dihydropyridine, have been investigated in a number of solvents and solvent mixtures. The effect of substituents on the solvatochromic behaviour of these compounds is described. All investigated merocyanines exhibited a strong negative solvatochromism. Inverse solvatochromism was observed in solvents of very low polarity for polar dyes, and in polar solvents for dyes containing hydrophobic substituents. This inversion of the solvatochromic behaviour is attributed to aggregation phenomena. Keywords: merocyanines, solvatochromism, betaine, aggregation.

A photoelectrochemical cell with oriented pigment—polymer complexes

Photovoltaic effects and photocurrent generation in electrochemical cells consisting of a layer of oriented pigment—polymer complexes sandwiched between two semiconducting electrodes have been investigated. The complexes of chlorophyll a, chlorophyll b and stilbazolium merocyanines with polyvinyl alcohol have been used. The electric and optical properties of the cells have been established. The cells exhibit a potential difference which is changed under illumination. The phenomenon observed is explained supposing the formation of different junctions between the sample and each electrode. This difference is related to an asymmetric distribution of charge across the cell. Surface states related to SnO 2 electrode decomposition are formed during aging of the cell. The cells investigated simulate to some extent biological membranes across which the redox components are distributed asymmetrically, enabling vectorial transfer of charge through the membrane.

A photoelectrochemical cell with oriented pigment-polymer complexes

Photovoltaic effects and photocurrent generation in electrochemical cells consisting of a layer of oriented pigment-polymer complexes sandwiched between two semiconducting electrodes have been investigated. The complexes of chlorophyll a, chlorophyll b and stilbazolium merocyanines with polyvinyl alcohol have been used. The electric and optical properties of the cells have been established. The cells exhibit a potential difference which is changed under illumination. The phenomenon observed is explained supposing the formation of different junctions between the sample and each electrode. This difference is related to an asymmetric distribution of charge across the cell. Surface states related to Sno 2 electrode decomposition are formed during aging of the cell. The cells investigated simulate to some extent biological membranes across which the redox components are distributed asymmetrically, enabling vectorial transfer of charge through the membrane.

Polarized spectra of a series of stilbazolium merocyanines in polyvinyl alcohol films

Polarized absorption, fluorescence and photoacoustic spectra of a series of stilbazolium merocyanines in stretched and unstretched polyvinylalcohol films were measured. Protonated dyes and free based are present in PVA films. The degree of orientation of the dye molecules depends on the substituents present in the molecule. The bulky t-butyl causes a decrease in the degree of orientation and prevents the formation of ground state complexes. In the excited state, the steric hindrance is less important and exciplexes are formed. Only ground state complexes and exciplexes fluoresce. The excitation of monomers is followed by effective thermal deactivation. Ground state complexes and exciplexes have different geometries. Axial deformation of PVA films favours excimer formation, but causes a partial dissociation of the ground state complexes.