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In a comprehensive picture of inclusion com- plex formation of the highly fluorescent dye coumarin-6 (C6) and betacyclodextrin (beta-CD), which was obtained using various fluorescence spectroscopic methods, it was demonstrated that up to three beta-CD rings can thread on the rod like dye molecule. Interaction of coumarins and modified coumarins with cellular organelles or proteins has been reported in several publications. Especially 7-amino- coumarins are characterized by unique properties like high fluorescence quantum yield and are thus already used successfully in different areas, like staining of fluorescent nanoparticles. We could show that Coumarin-6 made sol- uble by complexation with beta-cyclodextrin is able to stain eukaryotic cells specifically dependent on their origin and cellular behaviour. The staining reaction is indepen- dent from pH, is photo stable, and shows no cross talk with proteins in the cytoplasm and other staining procedures or erythrocytes. Staining with coumarin 6/cyclodextrin com- plexes can thus be used for fast discrimination of different cell types. Importantly, it could be shown that the ideal staining reaction is dependent on the stoichiometry of the complex-formation.

Lipid-polymer conjugates with differing hydrophobic to hydrophilic dimensions were prepared. The polymer part consisted of hydrophilic poly(2-methyl-1,3-oxazolines) (POZO), whose chain length can be controlled by living polymerization methods. The lipid-polymer conjugates were incorporated into vesicles composed of L-α-dimyristoylphosphatidylcholine (DMPC) or L-α-dipalmitoylphosphatidylcholine (DPPC) in amounts of up to 25 mol%. The formation of domains within the lipid bilayer membrane is observed by atomic force microscopy (AFM), thermal analysis (DSC), and fluorescence spectroscopy. The synthetic design of the lipids allows control over the distribution of polymer chains on the vesicle surface.

Fluorescence correlation spectroscopy (FCS) was used to study the diffusion behavior of the glucocorticoid dexamethasone on the cell membrane of the mouse pituitary cell line AtT-20 to investigate the putative membrane glucocorticoid receptor (mGR). This putative membrane receptor is thought to mediate glucocorticoid effects independent from protein synthesis and the well-known intracellular glucocorticoid receptor (iGR), the so-called “nongenomic” effects. The high spatial resolution of the FCS technique allowed for focusing exclusively on the cell membrane; measurements were taken on living cells in solution after incubation with 60 nM fluoresceindexamethasone for 1 h without manipulation of the cells. FCS measurements were performed by moving the position of the laser focus in 1 μm steps through a single cell. In a scan through the cell a component typical for a receptor-bound ligand (diffusion constant 3 x 10-10 cm2 sec-1) becomes apparent in the autocorrelation function (ACF) at the position of the cell membrane whereas another component (diffusion constant 2 x 10-8 cm2 sec-1) typical for a ligand diffusing in the cytosol becomes predominant in the ACF curves inside the cell. After pre-incubation with unlabeled dexamethasone in 1000-fold excess the “receptor-typical” component on the cell membrane was absent. This result is the first direct evidence for the existence of a mGR on a living cell.

The structures, spectroscopic and photophysical properties of the inclusion complexes between 4-OH-biphenyl and cyclodextrins (CD) in water were studied theoretically and experimentally. The complex structures were predicted using a dynamic Monte Carlo procedure including solvation effects and analyzed via computed and experimentally determined circular dichroism. The interpretation of the induced circular dichroism spectra indicated the formation of stable 2:2 complexes between the probe and alpha-CD, while 1:1 structures account for the circular dichroism induced by beta- and gamma-CD. Fluorescence emission quantum yields and lifetimes, measured as a function of the CD concentration, confirmed the formation of this higher order complex with alpha-CD. Prototropic equilibration in the singlet excited state was found to be depressed in 2:2 complexes due to the hydrophobic environment of the OH groups, while it remained unperturbed in 1:1 complexes, where the substituent is exposed to the aqueous environment. Triplet-triplet absorption and triplet quenching data supported this interpretation. The photophysical properties of both the 1:1 and the 2:2 complexes are characterized by a significant reduction of the nonradiative decay rates.

Acid–base properties of four 3,5-dimethyl-1,7-diphenyl-bis-pyrazolo-[3,4-b; 4′,3′-e]-pyridine derivatives with different substituents in position 4, i.e. N,N-dimethylaminophenyl, phenyl, nitrophenyl, and methoxyphenyl (DMA-DMPP, H-DMPP, NO2-DMPP, and CH3O-DMPP) were investigated in nonaqueous solutions. Absorption and stationary fluorescence as well as time-resolved spectroscopy were applied as methods. The acidity of the amino group in DMA-DMPP which is preferentially protonated in the ground state, does practically not change in the first excited state. The second protonation step of DMA-DMPP and the protonation of the other compounds occurs at the heterocyclic subunit, in the ground state most probably on the pyridine nitrogen. The basicity of this nitrogen atom increases remarkably in the first excited state. Experimental results were compared with those of semiempirical calculations. The amino group as the preferential site of protonation before the pyridine nitrogen in the ground state was confirmed. According to quantum mechanical computations, one pyrazolo nitrogen is preferentially protonated in the first excited state. The protonation is accompanied by a geometrical relaxation leading to a planarized conformer with a lower total energy.

Potential photosynthetic models, porphyrin dyads with various acceptors, that are separated by a diazaphenylene spacer, are synthesized by a new strategy. The amidine and vinamidinium salts are coupled by pyrimidine rings. In one example (n=1 in the figure), excitation of a flavin acceptor results in energy transfer to the porphyrin singlet (≈60 %) and population of a charge-separated state (≈40 %), which relaxes to the ground state on a subnanosecond time scale.

Fluorescence properties of 1-heptanoylpyrene in homogeneous solutions and incorporated into liposome membranes have been measured. The fluorescence intensity of the alkanoylpyrene is small in neat hydrocarbon solutions (Qf = 0.006) but increases with increasing solvent polarity. On the contrary, Qf of the 1-alkylpyrene is larger by a factor of 10 in a hydrocarbon solvent and decreases slightly in polar solvents. In alcohols the fluorescence yield of 1-heptanoylpyrene becomes considerably larger in comparison to a nonhydroxylic environment and nearly identical to that of heptylpyrene in the same solvent. The fluorescence spectra shift bathochromically in that polar environment. The fluorescence properties of 1-heptanoylpyrene incorporated in a liposome membrane indicate that the probe molecules are well embedded within the hydrophobic core of the bilayer. Semiempirical calculations were performed for 1-ethanoylpyrene and 1-ethylpyrene as model compounds in order to analyze the influence of solvent polarity and of hydrogen bonding on excited state energies and fluorescence properties of 1-acyl derivatives of pyrene. Hydrogen-bonding increases the energy gap between the lowest singlets, which are nearly degenerated, and the 3π*-n triplet and reduced consequently the intersystem crossing efficiency. But also a change in the sequence of the excited 1π*-π states is concluded from experimental data and should contribute to the increase of the fluorescence yield upon hydrogen bonding.

The photophysical properties of 4-(4′-N,N′-dimethylaminophenyl)-1,7-diphenyl-3,5-dimethyl-bis-pyrazolo-[3,4-b;4′,3′-e]pyridine (DMA-DMPP), highly emissive in non-polar solvents and composed from a dimethylanilino electron donor and a bulky electron acceptor, have been investigated. The position of the fluorescence maximum as well as the fluorescence quantum yield and the radiative decay rate are strongly solvent polarity dependent; the magnitude of this effect becomes dramatically larger as the solvent polarity exceeds that of 1-chlorobutane. In protic solvents dual fluorescence is observed. In accordance with theoretical calculations the results are explained in terms of a polarity induced change in the energetic ordering of two emissive states of largely different charge transfer character.

The complexation properties of various cyclodextrins depend on their ring size and the molecular shape of the guest molecules, but also on the hydrophobicity of the interior. Convenient systems for the characterization of the environment (solvation shell or complexing host molecules) are alkylaminomethyl-naphthols, molecules with an intramolcular hydrogen bond allowing proton transfer, which is extremely sensitive to solvation phenomena.

Solubility enhancement of the fungicide triflumicole byβ-cyclodextrin is explained using a thermodynamic approach. The influence of organic cosolvents on the overall equilibrium constants of triflumizole complexation withβ-cyclodextrin in aqueous solutions has been investigated. Their variance in mixed solvents is only partly explained by a competitive inclusion of substrate and cosolvent molecules inβ-cyclodextrin. The geometries of host-guest complexes have been estimated by molecular mechanics calculations. Their broad structural variety caused by the flexibility of host and guest molecules and different association possibilities of triflumizole have been analysed by a dynamic Monte Carlo docking method. The hydrophobic effect has been simulated by cominimization of the hydrophobic contributions to the solvation energy, calculated from the solvent accessible surface area of the complex and the conformational (potential) energy.

In addition to the yellow emission ascribed to the J aggregates of 1,1′-diethyl-2,2′-cyanine, this compound also exhibits a high-energy emission around 400 nm in dilute aqueous solutions (c

Steady-state and dynamic photophysical characteristics of a number of 4- and 5-amino-2-phenylindan-1,3-dione derivatives have been studied at 293 and 77 K in solvents of widely different polatiry and hydrogen-bonding ability. The observed changes of the fluorescence Franck-Condon transition energy, and of the fluorescence quantum yields and the singlet lifetimes, as well as the solvent deuterium-isotope effect, indicate the formation of intermolecular hydrogen bonds in the excited state with protic solvents for the 5-amino compounds at room temperature.

The photochemistry of some α-azohydroperoxides (phenyl(phenylazo)methyl hydroperoxide and its halogenated derivatives) was investigated in various solvents by microsecond and nanosecond flash photolysis methods and steady state product analysis. Photodecomposition of the molecule, demonstrated by the formation of benzaldehyde, is a major, but not the only, photochemical pathway. Investigation of the influence of solvent and substitution on the photoinduced transients provides strong evidence for alternative photoreactions. One of the species produced by flash photolysis was studied in detail and assigned to a transient zwitterion formed from the α-azohydroperoxide by proton transfer via an excited state pathway. Semiempirical calculations add further support to the proposed mechanism.

Piperidinomethyl-2-naphthol forms inclusion complexes with β-cyclodextrin with an equilibrium constant of 265M−1 in aqueous solution. The proton transfer equilibrium between the neutral and the zwitterionic form is strongly influenced by the association.

Solvent polarity effects on the energetics of charge separation processes, in particular on proton transfer in 1-morpholinomethyl-2-naphthol (M2N), were studied and discussed in the frame of a continuum model. The obtained results were compared to electron transfer (TICT) inp-cyano-N,N-dimethylaniline (CDMA). Solvatochromic shifts of M2N were explained by an increase of the molecular dipole moment on excitation, but more importantly by a rotation of its direction. A minimum in the excited state lifetime in an intermediate polarity region was attributed to a maximum radiationless transition probability.

The emission yields of 1-(N,N-dimethylamino)-2-phenylethane are followed as a function of the excitation energy in solutions in n-hexane, 1,2-dichloroethane, and in ethanol at room temperature. In n-hexane intramolecular exciplex formation is slightly more favoured from the excited amino than the aryl moiety. The conversion from the excited amine to the exciplex is partly quenched by dichloroethane. In ethanolic solutions excited amine does not convert to the lowest aryl π, π∗, but exciplex formation is observed following excitation of both chromophores.

The quantum yield O(e aq ) of photoejected electrons from aromatic carboxylate anions in aqueous solutions (pH 9.5 – 12.3) appreciably increases with increasing excitation energy; for example, O(e aq ) for benzoate is 0.0025 for the S 1 state (excitation at 254 nm) and 0.0048 for the S 2 state (excitation at 214 nm). The O(e aq ) value also increases with the number of CH 2 groups separating the phenyl and carboxylate groups; for example, for phenylbutyrate O(e aq ) is 0.05 for the S 1 state and 0.010 for the S 2 state. Furthermore, increases of O(e aq ) are linked with decreases in the quantum yield of fluorescence. In order to evaluate a possible consumption of the photoejected electrons by the ground state carboxylates, the rate constants k (e aq + substrate) for the reaction of solvated electrons with the corresponding substrates were determined.

Exciplex formation of triethylamine with ethanol and with deuterated ethanol at low alcohol concentrations in hydrocarbon solutions is shown by steady state and time-resolved fluorescence spectroscopy. The observed spectra and the decay kinetics show the appearance of three exciplex structures which can be discriminated by temperature and deuterium isotope effects. The spectrum of the primarily formed 1:1 heterodimer overlaps significantly with the monomer spectrum (spectral shift is 800 cm −1 ) and equivalent associations are found with tetrahydrofuran. The photophysical parameters change only slightly on complexation. Two further exciplex emissions with large spectral shifts compared with the monomer (4500 cm −1 and 9000 cm −1 ) arise at ethanol concentrations above 0.02 M, together with a diminution of the quantum yield. Complexation with non-deuterated ethanol leads primarily to high energy emissive structures and equilibrium is attained, as they decay with a common lifetime. Deuteration of ethanol results in a stabilization of the lowest energy exciplex, which is populated irreversibly. Exciplex structures are discussed, with reference to ab inition model calculations.

Fluorescence spectra, quantum yields and lifetimes are comparatively studied for aniline, N,N -dimethylaniline (DMA) and some further alkylsubstituted and rigid aniline derivatives in various solvents. A good correlation of Stokes shift with macroscopic solvent parameters is found for DMA but not for aniline. General and specific solvent effects are distinguished by studying the functional dependence of various spectroscopic and photophysical parameters on the polar co-solvent concentration in binary solvent mixtures. Excited state complexation of primary and secondary amines with alcohols is demonstrated by the double-exponential decay of the monomer fluorescence and the grow-in of exciplex emission found in aniline—ethanol— n -hexane ternary systems. Exciplex formation is attributed to solvent—donor hydrogen bonding and primarily causes enhanced intersystem crossing compared with that in the free molecule, an effect also evoked by N -methylation. Non-specific long-range interactions give rise to a general reduction in the non-radiative deactivation rate, with the exception of o,o′ -dimethyl-substituted anilines, for which an increase in this rate was found as the bulk becomes polar.

The effects of the excitation wavelength on the quantum yields Q(eaq−) and QF of electron ejection and fluorescence respectively were measured for 4-cyano-N,N-dimethylaniline (CDMA) and related compounds in aqueous solutions. In the case of CDMA no electron ejection was found for excitation of the long-wavelength (1La, 1Lb) band system. At shorter wavelengths (λexc

Exciplex formation between triethylamine and some alcohols in hexane solution has been followed by nanosecond time- and energy-resolved fluorescence spectroscopy. The experimental results have been discussed on the basis of a successive association model and rate constants have been obtained from an iterative adjustment of the model parameters to the measured concentration dependence of the decay times. Fluorescence quenching, increasing in efficiency with decreasing alcohol chain length, may be attributed to a charge transfer reaction of the amine—alcohol exciplexes with alcohol clusters formed in low concentration hydrocarbon solutions. The deuterium isotope effect observed in these systems can be explained by hydrogen migration in triethylamine—alcohol exciplexes.

Fluorescence spectra, quantum yields and lifetimes of p-cyano-N,N-dimethylaniline (CDMA) were studied in various binary mixtures of n -hexane with chlorinated hydrocarbons. Solvent effects on the equilibrium between normal emission and fluorescence originating from the highly dipolar twisted internal charge transfer (TICT) state arise predominantly from non-specific solute-solvent interactions. The non-radiative deactivation rate of the TICT state is affected primarily by the solvent composition and slows down with the stabilization of the TICT state in environments of high polarity.

Two primary photoreactions were observed for derivatives of 2-phenylindian-1,3-dione in various solvents: (1) cleavage of the hydrogen atom in the α position to both keto groups resulting in the formation of 2-arylindan-1,3-dion-2-yl radicals; (2) photoisomerization to benzylidenephthalides as a result of bond rupture via a Norrish type I mechanism. Both processes are possible with different quantum yields from the diketo form (in apolar solvents), from the enol form (in alcohols) and from the enolate form (in alkaline water).

The yields of fluorescence at 295 and 77 K and of phosphorescence at 77 K of phenol and anisole were determined in solvents of different polarities (hydrocarbons, ether, ethanol). Also intersystem crossing yields are reported for phenol and anisole in cyclohexane solution at 295 K. The data show that a non-radiative process, different from intersystem crossing, competes with the decay of S 1 phenol in liquid hydrocarbons. The nature of this deactivation pathway is discussed.

The influence of temperature and of various solvents on fluorescence and electron ejection has been studied using monophenylphosphate. Heavy atom quenching experiments with Cs+ ions and the temperature dependence observed for the system show that electrons are not only emitted from the thermalized singlet state of aqueous monophenylphosphate (Q= 0.02 for T= 30°C and pH = 8.2) but probably also during relaxation prior to fluorescence (Q= 0.008). The significant decrease in fluorescence at higher excitation energies can be satisfactorily explained by an increase in photodetachment of e–aq or H according to the pH of the solution (reaching 0.23 at pH 8.2). From the results it was concluded that electron ejection occurs via an intermediate state which has very similar properties to c.t.t.s. states observed in the spectroscopy of inorganic anions.

The dependence of the fluorescence quantum yield, QF, on the energy of the exciting light was examined for a number of aromatic amines (aniline, N,N-dimethylaniline, 2-phenylethylamine, etc.) in various polar and non-polar solvents down to 200 nm. QF of aniline is constant throughout the first absorption system but decreases when the excitation reaches the second band. This effect is most pronounced in hydrocarbon solutions but small in polar solvents capable of forming hydrogen bonds, with the only exception being water. For N,N-dimethylaniline a wavelength dependence of QF is observed only in aqueous solutions. Concomitant to the QF decrease the H2 evolution in hydrocarbons and electron ejection in water increase. These effects are also observed for solutions of 2-phenylethylamine and are explained by the formation of weak intramolecular complexes. A further pathway, characteristic of the benzoic ring, is assumed to be responsible for the wavelength dependence of protonated anilines. The derived deactivation pattern is of general validity for simple polar aromatics.

The dependence of the fluorescence quantum yield Q(F) on the excitation wavelength (λexc) was studied for phenol, anisole, p-cresol, p-methylanisole, 3,5-dimethylphenol and 2,4,6-trimethylphenol in polar and apolar solvents. All the systems investigated, with the exception of anisole and p-methylanisole exhibit a marked decrease in Q(F) at lower λexc values in hydrocarbon solvents. Further it was established that in this case enhanced photochemical cleavage of the OH bond is mainly responsible for this effect. Owing to the formation of H-bonds this dependence diminishes in polar, strongly associating solvents like alcohols and ethers, but not in water.