Janina R. Heldt

Photophysical properties of 4-alkyl- and 7-alkoxycoumarin derivatives. Absorption and emission spectra, fluorescence quantum yield and decay time

Abstract 4-Alkyl- and 7-alkoxycoumarin derivatives have been investigated for their spectroscopic properties in three different solvents. The substituents are methyl, ethyl, propyl and butyl groups. Absorption and emission spectra, quantum yields and mean fluorescence decay times have been determined. The spectroscopic studies together with calculations of the radiative transition probabilities indicate that the 4-alkyl- and 7-alkoxy substituents do not change the symmetry of the electronic cloud of the coumarin skeleton. The changes observed for the rates of radiative transitions and also for the positions of the absorption and emission maxima can be explained by changes in the molecular electronic transition moment, caused by the weak donation potential of the substituents. A strong dependence of the quantum yields and mean fluorescence decay times on solvent viscosity has been found, leading to the suggestion that torsional rotations of the alkyl and alkoxy substituents significantly increase the internal non-radiative energy conversion rate.

Electronic energy transfer efficiency of mixed solutions of the donor–acceptor pairs: coumarin derivatives—acridine orange

Abstract Excitation energy transfer between coumarin derivatives and acridine orange (AO) in solutions of two different viscosities has been studied. The rate constants of the electronic energy transfer ( k ET ) and critical radius ( R 0 ) were determined for coumarin derivatives as donors and AO as acceptor. The obtained values of k ET and R 0 indicate that dipole–dipole interaction between D–A pairs is responsible for the energy transfer mechanism. The experimental data of energy transfer efficiency are well described by the Forster theory.

Preferential solvation of fluorenone and 4-hydroxyfluorenone in binary solvent mixtures

Abstract Preferential solvation of fluorenone and 4-hydroxyfluorenone in binary solvent mixtures has been studied using steady-state spectroscopic measurements. This study concerns the solvent-induced shift of the absorption and fluorescence spectra of both molecules in two solvent mixtures, i.e., cyclohexane–tetrahydrofuran and cyclohexane–ethanol. The first system contains polar solute molecules, fluorenone and 4-hydroxyfluorenone, in a mixture of polar aprotic (tetrahydrofuran) and non-polar (cyclohexane) solvents. In the second solvents mixture, hydrogen bonding with solute molecules (ethanol) may occur. The results of spectroscopic measurements are analysed using theoretical models of Bakshiev, Mazurenko and Suppan which describe preferential solvation phenomena. In the case of cyclohexane–tetrahydrofuran mixtures, the deviation from linearity in the absorption and fluorescence solvatochromic shifts vs. the solution polarity is due to non-specific dipolar solvent–solute interactions. For cyclohexane–ethanol binary mixtures, both non-specific and specific (hydrogen bond and proton-relay tautomerization) interactions contribute to the observed solvatochromism.

Concentration and Temperature Dependence of Laurdan Fluorescence in Glycerol

Steady-state and time-resolved fluorescence measurements have been performed on Laurdan, dissolved in viscous glycerol, as functions of temperature and concentration. The results indicate spectral heterogeneity of the Laurdan solution. The fluorescence decay time distribution is attributed to radiative deexcitation of spatial conformational forms of locally excited (LE) and charge transfer (CT) states, the S1(CT)EQ state being in thermodynamic and vibrational equilibrium. The lifetimes and contributions of the different fluorescence modes depend on concentration and temperature. The excitation and emission spectra show discontinuous changes with increase of the Laurdan concentration.We suppose that the observed changes are caused by the formation of Laurdan micelle aggregates.

Laser emission of new phenyl-acetoxy anthracene derivatives

Abstract The observation is reported of laser action in eight new acetoxy-phenyl anthracene derivatives.

Spectroscopic studies of inclusion complexes of methyl-p-dimethylaminobenzoate and its ortho derivative with α- and β-cyclodextrins

The effects of α- and β-cyclodextrins (CDs) on the both emission modes (LE -locally excited and TICT -twisted intramolecular charge transfer) of the fluorescence spectrum of methyl-p-dimethylaminobenzoate (I) and its o-methoxy (II) derivative in aqueous solution have been investigated using steady-state and time-resolved fluorescence techniques. It is found that the intensity of both fluorescence bands increases with increasing concentration of α- and β-CD. The stoichiometries and equilibrium constants of the fluorophore-cyclodextrin inclusion complexes have been determined by steady-state fluorescence measurements. Performed spectroscopic studies demonstrate that in the case of I in α-CD and β-CD, both 1:1 and 1:2 inclusion complexes are formed, whereas only 1:1 inclusion complex is formed between II and β-CD.

Influence of DPPC Liposome Concentration on the Fluorescence Properties of PRODAN and LAURDAN

Fluorescence spectral features of PRODAN and LAURDAN in phospholipid vesicles of different phase states were investigated. The results indicate that in the liquid crystalline phase the dominant emission results from the charge transfer (CT) excited state, whereas in the gel state of the membrane the emission from the locally excited (LE) state dominates. The fluorescence time studies point out that there are two radiation modes, one starting from only vibrationally relaxed excited states S1(LE)ν ((S1(CT)ν) and the other from a totally thermally equilibrated state S1(LE)EQ (S1(CT)EQ). In accordance with the obtained decay time dependencies, the fluorescence emission from total nonequilibrated excited states consists of a dominant or minor radiation process in the LE or CT band emission

Luminescence studies of benzamide derivatives at room and low temperatures

In this study the luminescence spectra and fluorescence decay times of benzamide and its three derivatives have been measured at room and low temperatures in MCH, EPA and IP/EE mixtures. The bichromophoric derivatives i.e., N-phenylbenzamide and N,N′-methylphenylbenzamide yield dual fluorescence. The phosphorescence spectra of the molecules under study show a blue shift when non-polar rigid solvent is replaced with polar one. This effect, and the same λmax values of the phosphorescence bands indicate that the phosphorescence emissions originate from the (n, π*) state of the benzoic moiety. The small τ values of the S1(LE) state suggest that the rate constants of the excited state proton-transfer tautomer and TICT isomer creation processes are large. The τ values of molecules in the S1(LE), S1′(PT), and S1″(CT) states differ significantly.

Zeeman Effect of the 6 476 Å Mixed Multipole Line of Bismuth

The Zeeman effect of the 6 476 A mixed multipole (or so-called forbidden) line was studied with a Fabry-Perot interferometer and a tri-prism spectrograph in magnetic fields of 1.3, 1.5, 1.7 and 2.0 kG. The relative intensities of the ΔM = ± 1 and ΔM = 0, ± 2 transitions for longitudinal and transverse directions of observations are calculated as functions of the external magnetic field and electric-quadrupole admixture. The differences between the relative intensities of ΔM = ± 1 Zeeman patterns observed in two directions are due to the interference of the magnetic-dipole and the electric-quadrupole radiation. A comparison of the computed and experimental intensities shows that this line has predominantly a magnetic-dipole character with the percentage of the electric-quadrupole radiation in this line being about 18 ± 4.5%. This result is in good agreement with the value obtained by Garstang.

Heavy-atom effects in laser properties of 9-acetoxy-10-acetoxyhalogenophenylanthracene derivatives

Laser emission has been found for eight new 9‐acetoxy‐10‐acetoxyhalogenophenylanthracene. For these compounds the absorption threshold power, laser output energy, and lasing region have been determined. It has been found that derivatives possessing –OAc or heavy‐atom substituents in position 2′ or 6′ of the phenyl ring show laser properties differing distinctly from those compounds which have them in positions 4′, 3′ or 5′. These differences can be explained throughout by ‘‘internal heavy‐atom’’ effects and interaction—hydrogen bonding—of the substituted phenyl ring with the anthracene skeleton. This interaction shifts the triplet levels causing a decrease of T1–Tn absorption losses.