S. L. Bondarev

Fluorescent 5-alkynyl-2'-deoxyuridines: high emission efficiency of a conjugated perylene nucleoside in a DNA duplex.

Four fluorescent 5‐alkynyl‐2′‐deoxyuridines were studied in DNA oligonucleotides and their duplexes. The fluorescence response to hybridization differs dramatically for nucleosides containing a perylene fluorochrome either conjugated or not conjugated to the nucleobase. The conjugated nucleoside, 5‐(perylen‐3‐ylethynyl)‐2′‐deoxyuridine, shows enhanced long‐wavelength emission in the DNA duplex, in contrast to the blue fluorescence of perylene on a flexible linker (in 5‐[(perylen‐3‐yl)methoxyprop‐1‐ynyl]‐2′‐deoxyuridine), which is quenched upon duplex formation.

Picosecond dynamics of singlet excited states of oxotetrahydrobenzo[c]phenanthridine in protic and aprotic solvents

The spectral and kinetic properties of singlet excited states of two tetrahydrobenzo[c]phenanthridines—3,3-dimethyl-1,2,3,4-tetrahydrobenzo[c]phenanthridine-1-one (DTP) and 3,3-dimethyl-1,2,3,4-tetrahydrobenzo[c]phenanthridine-1-ol (DTP1)—are studied by picosecond absorption and luminescence spectroscopy in protic and aprotic solvents at 293 and 77 K. Based on the differences in the spectral and luminescent properties of DTP and DTP1, it was shown that the oxygen atom involved in the conjugation system of DTP is responsible for the formation of hydrogen-bonded complexes with alcohols. In the picosecond spectra of the induced absorption of DTP in n-hexane and acetonitrile, two bands peaked at 480 and 600 nm are observed, which are caused by the Tk ← T1-and Sn ← S1 absorption of DTP molecules solvated by the solvent by means of universal intermolecular interactions. In alcohols (methanol, ethanol, and n-propanol), an additional band is observed at 850 nm, which is caused by the Sm ← S1 absorption of hydrogen-bonded complexes. From analysis of the kinetics of the rise and decay of the induced absorption of DTP in n-hexane, acetonitrile, and alcohols, it is suggested that the main nonradiative channel in DTP is intersystem crossing.

Electronic structure and fluorescent properties of malononitrile-based merocyanines with positive and negative solvatochromism

The behavior of the positions and shapes of the fluorescence bands of di-, tetra-, and hexamethine merocyanine dyes with 3H-indolyliden (dyes 1–3) and benzoimidazolyliden (dyes 4–6) as electron-donating substituents and malononitrile as an electron-accepting substituent is studied by the method of moments in solvents of different polarity. The solvatofluorochromic shifts have been found to be smaller than the solvatochromic shifts not only for negatively solvatochromic merocyanines 4–6, but also for dyes 1–3 whose solvatochromism is positive. For dyes 4–6, cases of a change of the sign of solvatofluorochromism with respect to the sign of solvatochromism are revealed. These nontrivial effects are accounted for by transitions between the polyene and polymethine electronic structures of merocyanines in the fluorescence state S1 that occur with increasing medium polarity. In contrast to the absorption spectra of merocyanines 1–3, an increase in the chain length results in an increase in the vinylene shifts in the fluorescence spectra of these dyes, as well as in a decrease in the deviations and in the narrowing of the bands. This is explained by the fact that the electronic structure of these merocyanines in the S1 state is closer to that of the ideal polymethine (the cyanine limit) than in the S0 state. The fluorescence bands of merocyanines 4–6 are observed to be broader compared to the absorption bands. This broadening is caused by a change in the relation between intermolecular and vibronic interactions during absorption and emission of light. The interactions of these types have a decisive effect on the behavior of the Stokes shifts and fluorescence quantum yields of merocyanines 1–6.

Tetronic acid in reaction with aromatic aldehydes and 2-naphthylamine. Investigation of fluorescent and nonlinear-optical characteristics of compounds obtained

By Knoevenagel condensation and by three-component condensation 3-arylmethylenetetrahydrofuran-2,4-diones and previously unknown 8,11-dihydro-11-arylbenzo[f]furo[3,4-b]quinolin-10(7H)-ones were respectively synthesized. The luminescent spectra and nonlinear-optical characteristics of compounds obtained were investigated.

Thermochromism and thermofluorochromism of merocyanines with a positive solvatochromism

The thermochromism and thermofluorochromism of ethanol solutions of di-, tetra-, and hexamethine merocyanines based on 1,3-dihydro-1,3,3-trimethyl-(2H)-indol-2-yliden and malonodinitrile, having a positive solvatochromism as compared to the corresponding cationic and anionic symmetric dyes, are studied at T = 348, 293, and 4.2 K. It is found that, upon a decrease in the temperature, the absorption spectra exhibit bathochromic shifts of bands, an increase in the vinylene shifts, and a decrease in deviations, whereas the fluorescence spectra exhibit opposite changes. In this case, the differences in the shapes of the absorption and luminescence bands decrease so considerably that the bands become virtually mirror-symmetric. It is shown that the spectral and luminescent effects observed arise because, at high temperatures, the electronic structure of the ground state of merocyanines approaches that of neutral polyenes, whereas, at low temperatures, this structure is similar to the structure of ideal polymethine. Such a transformation of the structure is caused by an increase in specific electrostatic interactions (nucleophilic and electrophilic solvations) with a solvent, as a result of which the alternation of the charges of a chromophore increases, while its bond orders become equalized.

Influence of the Polarity of a Medium on the Photonics of a Merocyanine Dye with a High Quadratic Polarizability

The influence of the polarity of a medium on the spectral and luminescent properties of 2-[(2E,4E)-6-(1,3,3-trimethyl-2,3-dihydro-1H-2-indolyliden)-2,4-hexadienyliden]malononitrile (THDM) in solutions and polymer matrices is studied at room temperature under conditions of steady-state and pulsed laser excitation. A large bathochromic shift of the absorption spectra observed upon an increase in the polarity of a solvent is caused by a strong increase in the molecular dipole moment μ due to a transition of molecules from the ground state (μg = 7.6 D) to an excited Franck-Condon state (μFC = 33.5 D). Based on the solvatochromic data, the quadratic polarizability was calculated to be β = (3.2 ± 0.6) × 10−28 esu, which is close to the experimentally determined value βex = (3.9 ± 0.2) × 10−28 esu. A strong narrowing of the fluorescence spectra in comparison with the absorption spectra is observed upon an increase in the solvent polarity. This narrowing is explained by a decrease in the bond length alternation parameter and by weakening of vibronic interactions in the singlet excited state. The dynamic solvatofluorochromism of THDM in the picosecond range is caused by reorientations of molecules of the polar environment occurring during a time period consistent with the dielectric relaxation time of these molecules.

Structure and fluorescence properties of merocyanine dyes derived from dimethylbarbituric acid

The fluorescence properties of positively and negatively solvatochromic di-, tetra-, and hexamethinemerocyanines derived from 1,3-dimethylbarbituric acid in solvents of various polarities were studied. The range of solvatofluorochromic effect for these compounds is narrower than the range of solvatochromic effect. Extension of the polymethine chain of these compounds causes in the fluorescence spectra, in contrast to the absorption spectra, an increase in vinylene shifts, a decrease in deviations, and band narrowing. The electronic structure of the merocyanines was analyzed by the AM1 method. Transitions between the ideal states (neutral polyene, polymethine, and charged polyene) were examined. The electronic structure of the merocyanines in the excited state was found to approach the cyanine limit. Its attainment accounts for a sharp increase in the quantum yields of the fluorescence and a decrease in the Stokes shifts in going to higher vinylogs, and also with an increase in the solvent polarity for positively solvatochromic merocyanines and with its decrease for the negatively solvatochromic derivatives.

Synthesis of hydrobenzo[b]phenanthrolinone derivatives proceeding from 8-aminoquinoline, and their spectral and luminescent properties

By a three-component condensation of 8-aminoquinoline, aromatic aldehydes, and 1,3-diketones accompanied by the Hofmann-Martius rearrangement hydrobenzophenanthroline derivatives were synthesized. Their spectral and luminescence properties in ethanol solution were investigated at 293 and 77 K.

Synthesis, isomerism, and spectral luminescence properties of methyl hexahydrobenzo[a]acridine-9- and -[c]acridine-10-carboxylates

The three-component condensation of 1- or 2-naphthylamines, aromatic aldehydes, and methyl 2-(benzo[1,3]dioxol-5-yl)-4,6-dioxocyclohexane-1-carboxylate led to the formation of methyl 9-(cis,trans)-10-(1,3-benzodioxol-5-yl)-7-aryl-8-oxo-7,8,9,10,11,12-hexahydrobenzo[c]acridine-9-carboxylates or methyl 10-(cis,trans)-9-(1,3-benzodioxol-5-yl)-12-aryl-11-oxo-7,8,9,10,11,12-hexahydrobenzo[a]acridine-10-carboxylates. The spectral luminescence properties of compounds obtained were investigated in ethanol at 293 and 77 K.

Synthesis of methyl 12-aryl-9,9-dimethyl-11-oxo-7,8,9,10,11,12-hexahydrobenzo[a]acridine-10-carboxylate

A three-component condensation of 2-naphthylamine, aromatic aldehydes, and methyl 2,2-dimethyl-4,6-dioxocyclohexanecarboxylate afforded methyl (cis,trans)-12-aryl-9,9-dimethyl-11-oxo-7,8,9,10,11,12-hexahydrobenzo[a]acridine-10-carboxylates. Spectral luminescence and nonlinear optical properties of compounds obtained were investigated.