Recently, there has been an increased interest in natural polysaccharides, in particular, chitosan, which are widely used in medicine and industry. Chitosan labeled with fluorescein dyes acquires additional optical properties that can be used in sensing and delivery systems. Mechanism of binding of a polymer to a label largely determines the field of its possible applications. The quantum chemical calculation using the B3LYP/aug-cc-pVDZ theory level has been made in order to contribute to the understanding of intermolecular interactions. The geometry of fluorescein, eosin Y, and erythrosin B in the dianionic, monoanionic, and neutral quinoid forms interacting with chitosan has been optimized and the absorption spectra have been calculated using the time-dependent density functional theory taking into account the solvent. The comparison of the calculated absorption spectra with the experimental data has shown a major role of the electrostatic mechanism in binding of anionic dyes to the protonated chitosan groups.
Fluorescein and its halogenated derivatives representing a family of homologous dyes with the gradual substitution of halogen atoms for hydrogen ones are widely used in biomedicine as fluorescent probes. This stimulates the intense experimental and theoretical studies of their fluorescent properties in aqueous solutions. However, the theoretical calculations are complicated by the necessity of taking into account the effect of a solvent (water) in the explicit form and the need for effective basic sets. This is especially important for the dyes that contain heavy atoms. In this study, the quantum-chemical investigations of the dianionic form of fluorescein and its Br- and I-substituted derivatives (eosin Y and erythrosin B) have been carried out using the time-dependent density functional theory (B3LYP functional) implemented in the GAMESS software suite. The effect of a solvent has been considered in the framework of the modified Thomas polarizable continuum model. The calculations have been made for vertical (absorption and emission) excitations in the adiabatic approximation and at the nonequilibrium solvation. The results obtained for the nonequilibrium solvation are in excellent agreement with the experimental data for fluorescein and its halogenated derivatives.
Stimulated low-frequency Raman scattering (SLFRS) spectrum in dimethylformamide (DMF) was registered in the range from 0.1 to 1 cm-1. SLFRS is a result of the laser pulses interaction with acoustic oscillations of the associates, therefore knowledge of the SLFRS frequency shifts (and consequently associates eigenvibrations frequencies) gives possibility to estimate the size of DMF associates. Scattering was excited by pulses of a ruby laser with a narrow spectral line and recorded by Fabri-Perot interferometers. In the scattering spectrum SLFRS component was recorded with a frequency shift of 0.33 cm–1 (10 GHz), which corresponds to the size of associates of about 150 nm. Simultaneously with the SLFRS, stimulated Brillouin scattering was recorded in the backward scattering spectrum.
We used high adsorption properties of the cationic biopolymer chitosan to synthesize colloidal polymer particles (average size about 0.3 μm) with immobilized CdTe quantum dots (QDs) and organic dye (erythrosin B). A high local concentration of fluorophores bound to the particles (about 10–3 M), as well as a wide overlap of their optical spectra result in an efficient (up to 80%) Förster resonance energy transfer (FRET) from QDs ensembles to dye molecules. The FRET was registered by both steady-state (quenching of the donor and enhancement of the acceptor fluorescence) and time-resolved methods (decreasing of donor lifetime). The dependence of the transfer efficiency on acceptor concentration was analyzed within the scope of the Förster theory extended for the case of multiple energy transfer configuration. The average distances between the donor and acceptor as well as local concentration of fluorophores within particles were determined. It was demonstrated that the synthesized particles can be used as FRET-based sensitive probes for inter-fluorophore distance calculation within the range of 4 ÷ 9 nm.
Recently synthesized pyrrolanthrone, naphtho[1,2,3-cd]indole-6(2H)-one (PyAn), and its water-soluble derivative, 3(naphtho[1,2,3-cd]indole-6(2H)-one-2-yl) sodium propylsulfonate, are very promising for anticancer therapy due to both the fluorescent and cytotoxic properties. The present study is focused on the spectroscopic analysis of solvent effects in PyAn and its derivative. An increase of the solvent polarity results in the bathochromic shift in emission and absorption spectra that indicates the involvement of ππ*-type transition. The double linear correlation of Stokes shift with bulk solvent polarity functions (in terms of Lippert’s, Bakhshiev’s and Chamma-Viallet’s models) and microscopic solvent polarity parameter ( ) 30 N ET for aprotic and protic solvents is observed. Both general and specific solvent effects are revealed for the solute-solvent systems. Fluorescence quantum yield, fluorescence lifetime and excited-state dipole moment were defined for PyAn and its derivative in different solvents for the first time. The obtained information is of a great importance for the characterization of intermolecular interactions of drugs with biomolecules for the development of new drug delivery systems.
Doping of polymer particles by a fluorophores results in the sensitization within the visible spectral region becoming very promising materials for sensor applications. Colloids of biocompatible chitosan-based polyelectrolyte complexes (PECs) doped with quantum dots (QD) of CdTe and CdSe/ZnS (with sizes of 2.0-2.4 nm) were synthesized and characterized by scanning electron microscopy, dynamic light scattering, ζ-potential measurements, absorption and luminescence (including time-resolved) spectroscopy. The influence of ionic strength (0.02-1.5 M) on absorption and photoluminescence properties of encapsulated into PEC and unencapsulated quantum dots was investigated. The stability of the emission intensity of the encapsulated quantum dots has been shown to be strongly dependent on concentration of quantum dots.
Modeling of kinetics of photoprocesses in polyatomic molecules based on four-level energy scheme is carried out. The
model includes the processes in dye under cw photoexcitation and takes into account a reverse intersystem crossing and
photochemical reaction from the upper triplet states. The analytical time-dependent relation for dye concentration of the
initial form was obtained taking into account the contrast of rates of various photoprocesses and using of quasistationary
approximation. It was shown that rate constant of photolysis correlates with probability of intersystem crossing of the
dyes. For the xanthene dyes in gelatin it was shown that simple experimental method of cw laser photolysis combined
with the kinetic model could be effective technique of study of upper excited states participation.
Influence of excitation energy transfer in binary solid solution (<> in gelatin) on energy yield of photoproduct and diffraction efficiency of photochemical amplitude-phase light-induced grating is investigated. It is shown, that energy values necessary for photobleaching of eosin Y in mono and binary solutions are different. Their relative energy variation lies in the range 1,1-1,9 during all exposure time. Both the yield of photoproduct and diffraction efficiency of amplitude-phase light-induced grating can serve as the indicator of excitation energy transfer.
The laser irradiation of the thin films of solid solution of eosin in gelatinous matrix in the first and some upper dyes absorption bands leads to decrease of films optical density due to reaction of photoreduction. In the paper the kinetic of photoreduction of the dye eosin K in polymeric matrix in three cases of irradiation was experimentally investigated: a) irradiation by N2 laser (λ=337nm, second band of absorption, π=2 nsec, repetition rate-100 Hz, average power-2,2 mW), b) irradiation by Ar-laser (λ=488 nm, first band of absorption, 6,5-12 mW), c) under a simultaneous action of both Ar and N2-lasers. It was demonstrated that the most effective reaction of photoreduction took place in case of direct populating of upper singlet states with probable following nonradiative transition into equienergetic triplet states (energy ranges 35000-45000 sm-1).
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