Solute - solvent repulsion effects on the absorption spectra of anthracene in n-hexane investigated under high pressure.

The band positions in the UV-VIS absorption spectra of compressed solution of anthracene in n-hexane significantly depend not only on the dispersive but also on the repulsive solute-solvent interactions, what has so far been omitted. Their strength is determined not only by the solvent polarity but also by Onsager cavity radius changing with pressure. The results obtained for anthracene show that repulsive interactions should be included in the interpretation of barochromic and solvatochromic results of aromatic compounds.

Spectral and photophysical properties of cytisine in acetonitrile - Theory and experiment.

Spectral and photophysical properties of (-)-cytisine that is used as a smoking cessation aid, and which derivatives are promising tools in a treatment of neurological diseases, were investigated in acetonitrile, non-specifically interacting solvent with a polarity similar to water. The two chair conformers of cytisine were found the most stable in the ground state S and the lowest excited singlet state S(π,π*), wherein axial one was characterized by a significantly larger abundance, fluorescence lifetime 0.15 ns and fluorescence quantum yield 0.

Spectral and Photophysical Behavior of Cytisine in n-Hexane. Experimental Evidence for the S(n,π*) → S Fluorescence.

Spectral and photophysical properties of (-)-cytisine (the compound used as a smoking cessation aid and a potential drug in Alzheimer's and Parkinson's diseases) were investigated. The two conformers of cytisine, whose presence in the S state has been earlier proved by the NMR and IR methods as well as in theoretical calculation, in nonpolar n-hexane show a rarely observed prompt fluorescence from the S(n,π*) excited state. This observation is unambiguously evidenced by very small radiative rate constants of these two emitting conformers, k = 7.

Deactivation of 6-aminocoumarin intramolecular charge transfer excited state through hydrogen bonding.

This paper presents results of the spectral (absorption and emission) and photophysical study of 6-aminocoumarin (6AC) in various aprotic hydrogen-bond forming solvents. It was established that solvent polarity as well as hydrogen-bonding ability influence solute properties. The hydrogen-bonding interactions between S1-electronic excited solute and solvent molecules were found to facilitate the nonradiative deactivation processes.

An intermolecular hydrogen-bonding effect on spectral and photophysical properties of 6-aminocoumarin in protic solvents.

The paper presents results of the spectral (absorption and emission) and photophysical study of 6-aminocoumarin (6AC) in strong protic solvents with different hydrogen-bond acidity. The measurements of the fluorescence lifetime and quantum yield clearly show that in protic solvents intermolecular hydrogen-bonding interactions between solute and solvent molecules facilitate the nonradiative processes. It is suggested that in these solvents very efficient internal conversion due to intermolecular hydrogen-bonding is induced.

Radiationless deactivation of 6-aminocoumarin from the S1-ICT state in nonspecifically interacting solvents.

This paper presents the results of a spectral (absorption and emission) and photophysical study of 6-aminocoumarin (6AC) in the solvents with which this molecule interacts only nonspecifically (n-alkanes, tetrachloromethane and 1-chloro-n-alkanes) and in nitriles. The strong effects of the solvents on the emission spectra, fluorescence quantum yield and lifetime of 6AC were observed. The results of the steady-state and time-resolved photophysical study suggest the presence of very fast nonradiative deactivation processes.

Hydrogen bond effects in the ground and excited singlet states of 4H-1-benzopyrane-4-thione in water--theory and experiment.

The hydrogen bond energies for 4H-1-benzopyrane-4-thione (BPT) in its ground and two lowest excited singlet electronic states have been determined using ab initio methods. It was shown that the BPT molecule can form, as an acceptor, four relatively strong hydrogen bonds with water molecules, leading to a stable complex in the ground electronic state S(0). The hydrogen bonds involving the sulfur atom from the thiocarbonyl group were found to be stronger than those involving the oxygen atom from the benzopyran moiety.

Changes in energy of three types of hydrogen bonds upon excitation of aminocoumarins determined from absorption solvatochromic experiments.

Absorption spectra of 6-aminocoumarin (6AC) and 7-aminocoumarins (C120 and C151) were studied in polyfluorinated alcohols: (1,1,1,3,3,3-hexafluoroisopropanol (HFIP), 2,2,2-trifluoroethanol (TFE)), in water and in methanol, and compared to those taken in 1-chloro-n-alkanes. According to our results, the observed unusual blue-shift of a long-wavelength band in absorption spectra in strong protic solvents is direct evidence of significant weakening of a NH-O hydrogen bond. The results obtained for the aminocoumarins in HFIP, which in contrast to aliphatic alcohols does not form hydrogen bonds of the acceptor type, prove that the decrease in the energy of the NH-O hydrogen bond upon excitation to the lowest S(1)-LE state is significantly greater than the increase in the energy of hydrogen bonds made by the oxygen atom of carbonyl group OH-O.

Influence of hydrogen bonds and nonspecific interactions on the spectral and photophysical properties of the excited singlet states of 4-aminophthalimide in amine solution.

The hydrogen-bond and nonspecific interaction energies for 4-aminophthalimide (4-AP), often used as a probe, in the ground electronic and excited singlet states are determined using ab initio computational methods. It is shown that the 4-AP molecule can form three relatively strong hydrogen bonds with trimethylamine (TMA) and triethylamine (TEA), which leads to the formation of S(0)-complexes between the solute and solvent molecules. Only two of the hydrogen bonds with the amine group of 4-AP change significantly their energies upon excitation and deactivation.

Spectral and photophysical properties of thioxanthone in protic and aprotic solvents: the role of hydrogen bonds in S1-thioxanthone deactivation.

Spectral and photophysical properties of thioxanthone (9H-thioxanthen-9-one, TX) were determined in a few protic solvents (H2O, D2O, hexafluoro-2-propanol) and compared with those in aprotic solvents. On the basis of the time-resolved and steady-state emission measurements and available literature data, it has been shown that the dominant S1-TX deactivation process in protic solvents is the formation of the S1-complex. The important modes of deactivation of the S1-complex are fluorescence (phiF approximately 0.

Rapid fluorescence quenching of S2-xanthione by 3,3-diethylpentane in perfluorohydrocarbons.

Rapid fluorescence quenching of S2-xanthione by 3,3-diethylpentane has been studied in three perfluorohydrocarbons of different viscosities. The donor fluorescence decay in the presence of a quencher was fitted using the Smoluchowski-Collins-Kimball (SCK) model. The molecular parameters, R (the sum of the molecular radii), D (the sum of diffusion coefficients), and the specific rate constant of the process, kappa, were determined.