B. M. Uzhinov

Photochromic dihetarylethenes. 7. Synthesis of bis(thienylazoles), photochromic analogs of diarylethenes

Procedures for the synthesis of 4,5-bis[2,5-dimethyl(3-thienyl)]-1,3-azoles based on 1,2-bis[2,5-dimethyl(3-thienyl)]-2-hydroxyethan-1-one, 2-chloro-1,2-bis[2,5-dimethyl(3-thienyl)]ethan-1-one, and 1,2-bis[2,5-dimethyl(3-thienyl)]ethane-1,2-dione were developed. Dithienylethenic compounds in which the thienyl rings are linked through the azole rings exhibit photochromic properties.

Intramolecular Fluorescence Quenching of Crowned 7-Aminocoumarins as Potential Fluorescent Chemosensors

The effects of the nature of solvent, temperature and complex formation with alkali and alkaline-earth metal cations, as well as protonation, on the efficiency and the kinetics of fluorescence of 3-azacrowned 7-diethylaminocoumarins have been studied. For the crown-ethers under investigation, the ratio of a dipole moment to the radius of Onsager cavity Δ μ/ρ is a constant value, and a macrocycle does not affect Δμ and ρ. The fluorescence of coumarin 1 in acetonitrile is quenched by an electron donor, triethylamine, with the Stern-Volmer constant being equal to (0.474 ± 0.009) M−1. The decrease in coumarin 1 fluorescence quantum yield upon the introduction of N-alkylazacrown moiety into position 3 is caused by an intramolecular photoinduced electron transfer from the nitrogen atom of macroheterocycle to the coumarin moiety, where the excitation is localized. The fluorescence quenching has an activation energy 2.32 ± 0.05 kcal/mol in various hydrocarbons, and does not depend on the solvent viscosity. The fluorescence kinetics of free crowned coumarins in methanol is not monoexponential because of the existence of macrocycle conformers, or because of the hydrogen bond complex formation between the solvent and the nitrogen atom of macrocycle, in which the efficiency of intramolecular electron transfer is different. Upon complex formation with alkali and alkaline-earth metal cations and upon protonation, the fluorescence quantum yield increases and fluorescence decay becomes monoexponential.

Photochromic Dihetarylethenes: XVII. * New Synthesis of Photochromic N-Alkyldithienylmaleimides **

A new convenient procedure for the synthesis of photochromic N-alkyldithienylmaleimides was developed on the basis of the reaction of 3,4-bis(2,5-dimethyl-3-thienyl)furan-2,5-dione with primary amines. Photochromic properties of the products were examined.

Planar and twisted intramolecular charge transfer states of the excited proton transfer products of aminocoumarins

Abstract The excited state proton transfer (ESPT) reaction of aminocoumarins containing primary ( Ia, If ), secondary ( Ib, Ic ) and tertiary ( Id, Ie and IIa, IIb ) 7-amino groups was studied. The limiting value of the fluorescence quantum yield (φ′ ∞ ) of the ESPT product of the 7- aminocoumarins Id and Ie , containing an unfastened tertiary amino group, is unusually low in polar solvents (ethanol (EtOH), dimethylsulphoxide (DMSO)) in contrast with 7-aminocoumarins Ia-Ic and IIb . A decrease in solvent polarity results in a strong (more than 40-fold in cyclohexane) increase in φ′ ∞ , probably due to a decrease in the rate of non-fluorescent, cationic, twisted intramolecular charge transfer TICT) state formation.

Intermolecular excited state proton transfer reactions of diaryloxazoles

Abstract The acid-base interaction of diaryloxazoles (DAO) in the ground and excited states with proton donors in protic and aprotic solvents have been studied. The scheme of DAO-carboxylic acids interaction, including the formation of H-bond complex 1:1 and ionic pairs 1:2 and 1:3 have been proposed. The equilibrium constants of the complex formation and luminescence characteristics of DAO conjugated forms have been determined. It has been shown that the basicity of nitrogen atom of DAO increases at the excitation. In the presence of proton donor the excited state proton transfer reaction (ESPT) takes place. The reaction efficiency which characterizes the probability of the excited product formation in the reaction act is close to unity. This result agrees with the estimation of DAO ESPT efficiency, made on the basis of the least photochemical motion principle. ESPT in the system 2,5-di(biphenyl)-oxazole-trifluoroacetic acid in protic solvents (ethanol, acetic acid) takes place mainly by static mechanism at the excitation of H-bond complex 1:1. The effect of the base and acid structures and the solvent nature on the proton transfer reaction of DAO in the ground and excited states has been discussed.

Induced Intersystem Crossing at the Fluorescence Quenching of Laser Dye 7-Amino-1,3-Naphthalenedisulfonic Acid by Paramagnetic Metal Ions

The fluorescence and triplet state quenching of 7-amino-1,3-naphthalenesulfonic acid by paramagnetic metal ions have been investigated in an aqueous medium. The basic mechanism of the fluorescence quenching involves the static and dynamic electron transfer to the paramagnetic cation. The induced S1→T1 intersystem crossing at fluorescence quenching of the fluorophore by Cu2+ cation has been found. There is a correlation between triplet state quenching rate constants and values of the efficient paramagnetic susceptibility and spin of the cations. The rate constants for the quenching pathways have been calculated.

Fluorescence of crowned butadienyl dye and its metal complexes

The absorption and fluorescence spectra of complexes of butadienyl dye (1) with lithium, sodium, magnesium, and calcium cations in MeCN were investigated. The addition of Li, Na, Mg, and Ca perchlorates to the solution of dye 1 in acetonitrile results in a significant (up to 5900-cm−1) short-wavelength shift of the absorption spectrum and a small (about 200-cm−1) short-wavelength shift of the fluorescence spectrum. The recoordination reaction in metal complexes of 1 takes place by intramolecular mechanism. The fluorescence quantum yield of 1Li+, 1Na+, and 1Ca2+ is approximately two times higher than that for 1. It was supposed that Li+ cation coordinates predominantly with oxygen atoms of macrocycle and, hence, influences weakly macrocycle nitrogen atoms conjugated with a molecule π-system.

Photochromic dihetarylethenes. 11. Synthesis and photochromic properties of diarylethenes containing furan or furopyrimidine bridges

Procedures were developed for the synthesis of substituted bis(2,5-dimethyl-3-thienyl)furans based on 1,2-bis(2,5-dimethyl-3-thienyl)-2-hydroxyethanone. Dithienylethene structures in which the ethene fragment is involved in the furan or furopyrimidine system possess photochromic properties and their open forms exhibit fluorescence.

Structural relaxation of excited molecules of heteroaromatic compounds

The results of investigation into structural relaxation in the excited singlet state are summarized for a wide range of heteroaromatic fluorophores and some of the heteroaromatic cations. Particular attention is paid to the substantiation of the modern competitive models of structural relaxation (TICT and PICT). The spectral-and-kinetic parameters of the compounds and the rate constants for the formation of relaxed charge-transfer states are tabulated.

RADIATIONLESS DEACTIVATION OF EXCITED MOLECULES OF 4-AMINONAPHTHALIMIDES

The effects of alkylation of the 4-amino group, polarity and viscosity of a solvent, and temperature on the fluorescence ofN-(2,4-dimethylphenyl)imides of 4-amino-1,8-naphthalenedicarboxylic acid were studied. A decrease in the temperature and polarity of 4-dimethylaminonaphthalimide to decrease and have almost no effect on the rate of emissive deactivation of excited state. The abnormally low efficiency of fluorescence of 4-dimethylaminonaphthalimide in polar low-viscosity media at room temperature is associated with the formation of a nonfluorescent charge-transfer state. The increase in the rate of radiationless deactivation of 4-aminonaphthalimide in the alkylation of its amino group is associated with the increase in its electron-donor ability.