Fluorescence Spectra Of Solutions Research Articles

Structure of the Absorption and Fluorescence Spectra of Solutions of Silico-Organic Polymers

The spectroscopic characteristics of new π-linked polymers, whose main chain contains tetracoordinated silicon, acetylene groups, and 1,4-biphenyl or 2,7-fluorene, in chloroform have been investigated. It has been established that the spectral features of the absorption, fluorescence, fluorescence excitation, and fluorescence polarization spectra of these polymers are due to the inhomogeneous broadening of the electronic states of the centers of two types formed in the disordered polymer chain.

ACRIDINE SPECIES ADSORBED ON MODELS OF ATMOSPHERIC PARTICULATE MATTER AND THEIR ROLE IN THE PHOTODEGRADATION MECHANISMS UNDER N2 OR O2 ATMOSPHERES

Comparing the acridine absorption and fluorescence spectra in solution with those of acridine adsorbed on the atmospheric particulate matter models, the nature of the adsorbed species has been determined. On the surface of ammonium sulfate, the ground and excited state species are protonated acridines. For acridine on silica, alumina, and magnesium oxide surfaces, the hydrogen bonded and/or neutral acridine species were determined to be present. On silica, ground state protonated acridines are also present. On alumina, photoprotolytic reactions are proposed to occur because the emission of the protonated species was observed at 470 nm. The rates of acridine photodegradation on the different surfaces were measured under a nitrogen atmosphere: the observed tendency for these was: (NH4 2SO4 > MgO > Al2O3 > SiO2. The rates are larger on surfaces were the hydrogen bonded and neutral species exist. Species on (NH4)2SO4 showed an unusually large rate of photodestruction. The rates under an O2 atmosphere were slower (than under N2) for acridine on MgO, Al2O3, and SiO2, and equal for acridine on (NH4)2SO4.

Fluorescence Probing of Self-Assembled Monolayer with Terphenyl-Derivatized Disulfides

The formation processes of and molecular ordering in self-assembled monolayers were investigated by fluorescence probing with p-terphenyl chromophores binding to disulfides at the o- or p-positions. In mixtures with dodecanethiol, the derivatized disulfides formed ordered monolayers. As compared with the broad monotonic fluorescence spectra in solutions, their emission bands were split into distinct peaks upon chemisorption on gold substrates due to intermolecular interactions between adjacent terphenyl groups. Their emission peak positions were interpreted in terms of the exciton coupling of various dimeric terphenyl configurations in the monolayers depending on the o- and p-isomeric structures.

Fluorescence of the cis-dimers of porphyrins containing ethylene bridges

The absorption and fluorescence spectra of solutions of the porphyrin dimers containing ethylene bridges, binding two Zn(II)octaethylporphyrin molecules or one Zn(II)octaethylporphyrin and one octaethylporphyrin molecule into cis conformation, were studied. For both studied cis-dimers, structureless absorption spectra were observed, only in general resembling the spectra of initial molecules, as well as weak fluorescence with a wide bell-shaped spectrum with a maximum at 680–700 nm and a quantum yield of about Φf≈3×10−5, which is three orders of magnitude lower as compared to the fluorescence of initial monomeric porphyrins. A strong dependence of the fluorescence yield on a medium viscosity was revealed. In addition, low-yield irreversible cis-trans photoisomerization of cis-dimers was detected. A mechanism responsible for the strong intramolecular quenching of fluorescence of the porphyrin dimers containing ethylene bridges is suggested to be a conformation transformation in the region of the ethylene bridge, leading the molecular system to the region of “conic crossing” of the energy surfaces of excited and ground electron states.

Semiempirical calculation of the absolute solvation shift of electronic and vibrational spectra of molecules in the gas-solution phase transition

Calculations of the main components of the absolute solvation shift of Δυ∑a, f, R optical absorption, emission, and Raman spectra of molecules in the gas-solution phase transition for solutions of several diatomic (HCl, DCl, H2, D2) and polyatomic (anthracene, 3-and 4-aminophthalimide) substances in some polar and nonpolar solvents are presented. The calculations are made by a new method of the semiempirical theory, which was proposed by the author earlier and makes such calculations possible for the first time. It is shown that the given theory adequately describes the photophysical effect under study and provides a correct prediction of the values of Δυ∑a, f, R, which differ for different systems by more than three orders of magnitude (from several inverse centimeters for vibrational spectra of H2 and D2 to many thousands of inverse centimeters for electronic fluorescence spectra of solutions of aminosubstituted derivatives of phthalimide).

Spatial and Spectral Heterogeneity in Fluorescence from Monolayers of 4-(4-(Dihexadecylamino)styryl)- N-methylpyridinium Iodide

Far-field fluorescence of Langmuir−Blodgett (LB) films of the hemicyanine dye, 4-(4-(dihexadecylamino)styryl)-N-methylpyridinium iodide, I, is spectrally heterogeneous, displaying bands assigned to monomer and various aggregated species in both excitation and emission. LB films of I visualized by epifluorescence microscopy were also observed to be spatially heterogeneous. Under the preparation conditions used here the morphology consists of coexisting liquid expanded (LE) and liquid condensed (LC) phases. LC domains display distinct spatial structure. They are ca. 5−20 μm in lateral size, display a multilobed shape, and are surrounded by LE phase. The characteristic aggregation behavior of these stilbazolium-based hemicyanines allowed their electronic spectra to be used to provide the contrast in fluorescence microscopy of LB films of I. Emission images thus reveal the aggregation-induced electronic structure of the molecules composing the domains. The degree of internal structure of the LC domains was observed to vary with excitation wavelength with the richest internal structure being observed with UV excitation of the fully developed H-aggregate. Correlation of film and solution fluorescence spectra suggest that the LC domains are composed of dimers, trimers, and larger n-mers up to the fully extended aggregate, while the LE phase is predominantly populated by monomers with some fully extended aggregates.

Spectral-luminescent properties and photoinduced transformations of bisanthene and bisanthenequinone

Based on the study of photochemical transformations of bisanthene in oxygen-containing solutions, it was established that the final product of this reaction is bisanthenequinone. It is shown that in the course of this oxidation reaction the intermediate compounds endomonoperoxide and bisanthene endobiperoxide are formed. Quantum-chemical calculation of the geometrical structure and electronic spectra of the endoperoxides has shown that they have a nonplanar structure, and their absorption spectra experience a large hypsochromic shift. The absorption and fluorescence spectra of solutions of bisanthene in different solvents at 300 and 77 K were investigated. The large Stokes shift of the fluorescence spectra of the solutions of bisanthene in benzene and in its methyl derivatives is explained by the action of intermolecular interactions. The quasi-line fluorescence spectra of solutions of bisanthene in the matrices of saturated hydrocarbons were recorded.

Structural, spectroscopic and photophysical analyses of substituted terthiophenes and quinquethiophenes as well as their corresponding polyesters

In this study, we present spectroscopic and photophysical results on oligothiophenes (trimers and pentamers) substituted with alkyl side chains as well as on the respective molecules incorporated in polyesters. The same oligothiophenes having two different electron acceptor groups, namely the carbonyl chloride and the acid substituent, at each end of the molecules have also been studied. These molecules provide a better correlation with their corresponding polyesters. Absorption and fluorescence spectra in solution are used to discuss the effect of the substitution as well as the length of the thiophene chain on the molecular conformation. Semiempirical calculations (AM1 and PM3) have also been performed to obtain the torsional potentials of the oligomers. Consequences of the conformational changes on the spectral and photophysical properties (fluorescence quantum yields, lifetimes and decay constants) of the various oligothiophenes and polyesters are examined. It is found that insertion of two alkyl chains on the central thiophene ring creates an important molecular twisting in the molecules. The length of the thiophene chain as well as the presence of end-substituents do not significantly influence the ground state molecular conformation. In the excited state, all molecules relax to more planar conformations. The fluorescence quantum yields and lifetimes are smaller for the alkyl-substituted molecules (without end-substituents) giving rise to higher values of the nonradiative decay constants compared to those of the unsubstituted molecules. This behavior might involve a decrease of the singlet–triplet energy gap for the twisted molecules which could enhance the intersystem crossing process. The incorporation of terthiophene and quinquethiophene derivatives in polyesters does not significantly change their conformation in the ground and excited states as well as their optical and photophysical properties.

Synthesis of Polymers with Isolated Thiophene-Based Chromophores

The polymers presented in this paper are designed for the intended use in light-emitting diodes. The synthesis of a new series of macromolecules containing isolated oligothiophene, oligothienylene vinylene, or bithiazole conjugated units bridged by aliphatic units is presented along with optical characterization by UV−vis absorption and fluorescence spectra in solution. These polymers gave very similar optical traits to their corresponding subunits while possessing the physical characteristics of a macromolecule.

Vinyl monomers bearing chromophore moieties and their polymers. I. Initiation and photochemical behavior of N‐acryloyl‐N′‐phenylpiperazines and their polymers

Two novel acrylic monomers bearing aromatic tertiary amino groups, i.e., N-acryloyl-N′-phenylpiperazine (APP) and N-methacryloyl-N′-phenylpiperazine (MPP) are synthesized by the reaction of N-phenylpiperazine and the corresponding acryloyl chlorides in the presence of triethylamine. They can be polymerized easily by using AIBN as an initiator or photopolymerized without any sensitizer. The photochemical behavior of APP, MPP, and their polymers are explored by recording the fluorescence spectra in solution. It has been found that the fluorescence intensities of these monomers are dramatically lower than those of their polymers in the same chromophore concentration, and such phenomenon is termed as “structural self-quenching effect” (SSQE). The strong fluorescence of these polymers can be quenched by adding electron-deficient monomers which have no chromophore moieties such as MMA, AN, etc., and their Stern–Volmer constants are determined. It is observed that the higher the electron-deficiencies of the quenchers, the higher the Stern–Volmer constants, which means stronger quenching effect. The SSQE displayed by APP and MPP make them useful as probes to pursue their photopolymerization process. As polymerizable aromatic tertiary amines, APP and MPP themselves or combining with organic peroxides such as BPO can initiate the photopolymerization or thermal polymerization of vinyl monomers such as MMA, AN by free radical nature, and at the same time enter the polymer chain. © 1996 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 34:1881–1888, 1996

Vinyl monomers bearing chromophore moieties and their polymers. I. Initiation and photochemical behavior ofN-acryloyl-N?-phenylpiperazines and their polymers

Two novel acrylic monomers bearing aromatic tertiary amino groups, i.e., N-acryloyl-N′-phenylpiperazine (APP) and N-methacryloyl-N′-phenylpiperazine (MPP) are synthesized by the reaction of N-phenylpiperazine and the corresponding acryloyl chlorides in the presence of triethylamine. They can be polymerized easily by using AIBN as an initiator or photopolymerized without any sensitizer. The photochemical behavior of APP, MPP, and their polymers are explored by recording the fluorescence spectra in solution. It has been found that the fluorescence intensities of these monomers are dramatically lower than those of their polymers in the same chromophore concentration, and such phenomenon is termed as “structural self-quenching effect” (SSQE). The strong fluorescence of these polymers can be quenched by adding electron-deficient monomers which have no chromophore moieties such as MMA, AN, etc., and their Stern–Volmer constants are determined. It is observed that the higher the electron-deficiencies of the quenchers, the higher the Stern–Volmer constants, which means stronger quenching effect. The SSQE displayed by APP and MPP make them useful as probes to pursue their photopolymerization process. As polymerizable aromatic tertiary amines, APP and MPP themselves or combining with organic peroxides such as BPO can initiate the photopolymerization or thermal polymerization of vinyl monomers such as MMA, AN by free radical nature, and at the same time enter the polymer chain. © 1996 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 34:1881–1888, 1996

Spectroscopic properties of fluorescence dye fura-2 with various divalent cations.

We examined the effects of divalent cations on the fluorescence excitation spectra of fura-2 from a 2 ml solution containing 1 microM fura-2 with an excitation wavelength of 300-425 nm and an emission wavelength of 500 nm. The fluorescence spectra in solutions of fura-2-Ca2+, fura-2-Ba2+, and fura-2-Sr2+ complexes show almost the same pattern. The dissociation constants (Kd) of Ba2+ and Sr2+ with fura-2 were 1.63 and 9.02 microM, respectively, and these values were higher than that of the Ca2+ complex (222 nM). The effect of Mg2+ binding on the fluorescence of fura-2 was quite small, and Mn2+ quenched the fluorescence of fura-2. The spectra of the fura-2-Ca2+ complex were changed by the co-existence of another divalent cation. Divalent cations competitively bind to the binding site of fura-2 and show the respective fluorescence spectra; consequently, the composed fluorescence spectra according to the respective Kd.

Temperature and Gatewidth Dependence of the Solid-Matrix Fluorescence Spectra of Stereoisomeric Tetrols

A unique laser-based method was developed for the solid-matrix fluorescence characterization and identification of tetrols, which are the hydrolysis products from benzo[ a]pyrene-DNA adducts. By employing different gatewidths with a boxcar integrator, we obtained the fluorescence spectra of the four tetrol isomers adsorbed on 10% α-cyclodextrin/NaCl at several temperatures. The data showed that the fluorescence spectral characteristics of the tetrols were both gatewidth- and temperature-dependent. The experimental conditions were optimized to identify the tetrols which had only minor structural differences. Applications of the gatewidth-dependence method both at room temperature and low temperature were considered. The low-temperature approach has the potential for the application to several species over a range of fluorescence lifetimes. The differences in the fluorescence spectral properties were partially explained by the rotation of functional groups in the tetrols and the solid matrix during the time frame of obtaining the spectra. Comparisons were made among the solid-matrix fluorescence spectra and the solution fluorescence spectra of the tetrols, and the solution fluorescence spectra of pyrene and the solid-matrix fluorescence spectra of pyrene.

An artificial photosynthesis porphyrin tetrad molecule for photoelectric conversion

A new artificial photosynthesis porphyrin tetrad compound of porphyrin-terephthahc acid ester-viologen-carbarzole (1) was synthesized and compared with two triad compounds (2a, 2b) and two diad compounds (3a, 3b) for photoelectric conversion. The absorption and fluorescence spectra in solution and in binary solvent were investigated; especially, the effects of aggregation on the photophysical properties were studied. A mechanism including photoinduced electron transfer and multistep charge separation for tetrad compound was suggested. By using the LB technique, the synthetic molecular devices were prepared with molecules 1, 2a, 2b, 3a, 3b and the model compound of porphyrin (4b), respectively. With only one monolayer of tetrad LB film on the surface of SnO2 conductive glass, rather high photodriven voltage and current were obtained.

Identification of Tetrol I-2 by Laser-Excited Solution Fluorescence Spectra

The detection and quantitation of the tetrols are important ways to study the extent of chemical damage to DNA. Both room- and low-temperature laser-excited solution fluorescence spectra of the four tetrol isomers were compared for their spectral features. The results showed that the characteristics of the solution spectra obtained at 77 K provided a very reliable means for distinguishing tetrol 1–2 from its isomers. By utilizing both room-temperature solid-matrix (10% α-cyclodextrin/NaCl) fluorescence spectra from earlier work and solution florescence spectra at 77 K obtained in this work, it is possible to identify the four tetrol isomers.

On the source of the anomalous fluorescence of ethyl esters of 4-(dialkylamino)benzoic acid in aromatic solvents: the role of exciplexes

Three excited species, denoted by N, X and E, are shown to account for the fluorescence spectrum of solutions of alkyl esters of 4-(dialkylamino)benzoic acid (DAAABs) in benzene and toluene. A reaction scheme indicating that the initially excited species N is the precursor of species X, that species N is not the direct precursor of species E, and that a reversible interconversion between the species X and E takes place, is suggested. Grounds for this suggestion are provided. The molecular structure of both N and X does not change when the solvent is changed from a saturated into an aromatic hydrocarbon. We suggest that the amino substituents in DAAAB have moved into closer proximity of the benzene ring in X than in N. Strong indications for the identification of E with a 1:1 exciplex, formed by one aromatic and one DAAAB molecule, are presented. From the dependence of the position of the fluorescence bands on the dielectric properties of the solvent, the electric dipole moment of species X in ethyl 4-(diethylamino)benzoate (DEAEB) and of the DEAEB-benzene exciplex was estimated to be 11±3 D and 23±5 D, respectively. The dipole moment of species X corresponds very well with the value of 12.2 D, determined by dielectric loss measurements. The change in entropy, Δ S, accompanying the 1:1 exciplex formation and the 1:1 exciplex stabilization energy, Δ H, are derived from the time dependence of the fluorescence as a function of both temperature and the concentration of the aromatic solvent. The results indicate that the 1:1 exciplex formation corresponds with an exothermic reaction with an unfavourable entropy factor. Both Δ S and Δ H do not depend on the size of the alkyl substituents of the amino group, i.e. the stability of X remains constant, when both substituents are larger than a methyl group. When methyl groups are chosen as substituents on the amino group in the DAAAB molecule, the stability of species X is diminished. This is explained by a less effective interaction between the accumulated electronic charge in the benzene ring in DAAAB and the small polarizability of a methyl group. The lifetime of the exciplex is demonstrated to be temperature independent, whereas the lifetime of X is shown to be governed by two different thermally activated processes.

Fluorescence properties of plastoquinol, ubiquinol and α-tocopherol quinol in solution and liposome membranes

It was found that plastoquinol-9, ubiquinol-10 and α-tocopherol quinol show intrinsic fluorescence in organic solvents and in liposomes. Their fluorescence spectra in solution showed the presence of one emission band with maximum intensity in the range 319.0–327.0 nm for plastoquinol and 321.5–326.5 nm for α-tocopherof quinol, which is the longest wavelength shifted in polar solvents. The emission band at about 371 nm for ubiquinol was not sensitive to solvent polarity. For all three prenylquinones the fluorescence quantum efficiency changed significantly in solvents of different polarities, being the highest in ethanol and the lowest in hexane in the case of plastoquinol and α-tocopherol quinol, whereas ubiquinol fluorescence showed the opposite effect. These spectral parameters were applied to determination of prenylquinol localization in liposome membranes.

Spectroscopic characterization and Langmuir–Blodgett monolayers of N,N′‐unsymmetrical dialkyl‐3,4:9,10‐perylenebis(dicarboximide)s

AbstractThe spectroscopic characterization of N‐pentyl‐N′‐R‐unsymmetrical dialkyl‐3,4:9,10‐perylenebis(dicarboximide)s (R = CH3, C2H5 and C3H7) is reported. Langmuir monolayers of all three non‐amphiphilic molecules were successfully prepared and transferred to solid substrates. The absorption and fluorescence spectra of solutions and Langumuir–Blodgett (LB) films were studied. Vibrational fundamental frequencies were observed using surface‐enhanced resonance Raman scattering and transmission and reflection–absorption Fourier transform infrared spectroscopy. The formation of aggregates in the ground and excited states (excimer formation) is also discussed.

Light-induced electron transfer of porphyrin triad for photoelectric conversion

Two new triad model compounds of porphyrin-viologen-carbazolen (1a and 1b) with different chain length were synthesized to mimic photosynthesis. The absorption and fluorescence spectra in solution, in micelle solution as well as in binary solvent, were investigated; especially, the effects of aggregation on the photophysical properties were investigated. A mechanism including photoinduced electron transfer and two-step charge separation was suggested. These triad compounds were easily formed LB films. Rather high photodriven voltages and currents were obtained with only one monolayer of LB film on the surface of SnO{sub 2} conductive glass. 25 refs., 12 figs., 2 tabs.

Structure, spectral-luminescence properties and photo-oxidative stability of structure-coloured aromatic polyamides

The absorption and fluorescence spectra of solutions and films of polymetaphenyleneisophthalamide with fragments of diaminoanthraquinones in the chain, and also aminobenzoylamino and dibenzoylamino derivatives modifying the chromophoric groups of the chain are studied. On the basis of a comparative analysis of the spectral-luminescence properties of the given materials the character of the alteration of chromophoric groups in the macromolecules is established. In the case of polyphthalamide modified with 4,8-diamino-1,5-dioxyanthraquinone units, the special features of the photo-oxidation and accumulation of free radicals are studied. It is shown that the quantum yields for the absorption of oxygen and the formation of carboxyl groups by films of this polymer, irradiated with light of λ = 240–280 nm is lower by a factor of 1.63 and 1.24 respectively than for films of unmodified polyphthalamide.