Józef 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.

Chemiluminescent studies of excited Mg and Sr atoms with Cl2 in the beam-gas arrangement☆

Abstract The chemiluminescence resulting from the reactions M* + Cl 2 → MCl* + Cl (M = Mg, Sr) has been observed when an atomic beam of Mg or Sr containing a considerable fraction of atoms excited to the long-lived 3 P states is intersected by an uncollimated beam of molecular chlorine.

Dielectric medium interactions in proton-transfer and charge-transfer mole electronic excitation

Abstract The competitive triple fluorescence of benzanilide are discerned by the application of specific solvent-solute interactions. The normal fluorescence S1 → S0 is in the UV region adjacent to the first absorption band, but the long-wavelength 500 nm fluorescence region is shown to involve an intermolecular proton-transfer fluorescence S1(PT) → S0(PT) and a twisted intramolecular charge-transfer fluorescence S1(CT) → S0. The variation of fluorescence band half-width and of the fluorescence band wavelength shift with dielectric constant are used to resolve the superposed fluorescences. The specificities of the solvent interactions offer a quantitative tool for molecular liqiud interaction studies.

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

Michael Kasha: From Photochemistry and Flowers to Spectroscopy and Music

A brilliant scientist and an outstanding personality who was one of the founders of modern photochemistry-Michael Kasha-is the subject of this Essay. Kashas rule and the Kasha effect both bear his name, and he also discovered the chemical production of singlet molecular oxygen, and was a pioneer of excited-state proton transfer systems. Kasha combined his passion for chemistry and physics with that for music, photography, and botany.

Stark effect of atomic helium second triplet series in electric fields up to 1600 kV cm−1

We present experimental and theoretical investigations of the spectral series 2 3 P‐n 3 Q (n = 3‐10, Q = S, P, D,...,n 1) in electric fields up to 1600kVcm 1 . Such fields cause—for n >6—shifts of the upper levels of the observed transitions which are larger than the separation between levels with different principal quantum numbers. The patterns belonging to a certain principal quantum number become similar to hydrogen patterns; they are nearly symmetric and show a nearly linear Stark shift in higher electric fields. The applied fields were high enough that patterns belonging to neighboring principal quantum numbers begin to overlap, which leads to interesting level-anticrossing effects. The experimental results are compared with numerical calculations taking into account mixing between states of different principal quantum numbers and also between singlet and triplet states. The agreement between experimental and theoretical line shifts is quite good.