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The lowest excited singlet states of 4-(dimethylamino)-4‘-cyanostilbene (DCS), 4-(dimethylamino)-4‘-nitrostilbene (DANS), and 4-di(hydroxy-ethyl)amino-4‘-nitrostilbene (DANS-diol) have been investigated by high-resolution fluorescence excitation and dispersed emission spectroscopy on samples seeded in supersonic expansions. Using ab initio calculations of the harmonic force fields of the electronic ground state as a starting point for the analysis of vibrational modes and frequencies, detailed vibrational assignments of the rich line structure of the S1 ← S0 transition in these three push−pull stilbenes are reported. From the experimental and theoretical analysis, it becomes apparent that the excitation spectra are dominated by low-frequency vibrational modes of the stilbene-like backbone, albeit that a characterization in terms of trans-stilbene vibrational terminology is not very appropriate. The fluorescence excitation and emission spectra show significant Franck−Condon factors for transitions involvin...

The copolymers of tetrachloroethylacrylate (TeCEA) and pentafluorophenylacrylate (PFPA) and of TeCEA and pentafluorophenylmethacrylate (PFPMA) have been examined with regard to their applicability as core materials for optical waveguides. In particular, their thermal properties as function of polymerisation conditions have been investigated and optimized by addition of crosslinkers. The polymerisation reactions were followed by FT-Raman and FT-IR spectroscopy. Also the optical characteristics like material dispersion and attenuation of the polymers have been studied. The fundamental demands of waveguide polymers are high optical transmission at the near-IR wavelengths windows around 1300 and 1550 nm, respectively, the adjustability of the refractive index of the core polymer versus the cladding polymer, and sufficient thermal stability of at least 70°C. Both the examined copolymers show low absorption at 1300 and 1550 nm of 0.2 and 0.7 dB/cm (best values), respectively. The refractive index (RI) of TeCEA/PFPA copolymer is tunable between 1.464 and 1.518 (1300 nm). TeCEA/PFPMA copolymers are tunable between RI values of 1.469 and 1.518 (1300 nm). Thermal stability as indicated by the glass transition temperature (Tg), which reaches about 81°C for the TeCEA/PFPA copolymer with 5 weight% (wt%) of ethyleneglycoldimethacrylate (EGDMA) crosslinker, whereas for TeCEA/PFPMA copolymer with the same amount of EGDMA a Tg of 105°C is obtained. As determined by quantitative vibrational spectroscopy the conversion in the all-acrylate based copolymer is in the order of 98%. Using also EGDMA as crosslinker and with an additional thermal treatment the unsaturation in photocured TeCEA/PFPMA copolymer can be decreased to values of 4%.

The photo-polymerization of tetrachloroethylacrylate (TeCEA), pentafluorophenylacrylate (PFPA) and pentafluorophenylmethacrylate (PFPMA) was examined by quantitative FT-IR and FT-Raman spectroscopy and by thermal analysis. The agreement between the FT-Raman results and thermal analysis was good for all monomers. The FT-IR measurement yielded higher percentages of unsaturation than the two other techniques in the slowly reacting PFPMA polymer, which can be attributed to oxygen quenching effects. Calculations of unsaturation based on spectroscopic measurements were carried out using the relative band ratio method. The influence of the choice of the internal reference band on the unsaturation calculation was examined. The photo-polymerization of the acrylates reached conversions of 95%–99% after irradiation of only a few minutes, samples which contained PFPMA reached conversions of about 85% after 1.5 h of irradiation. Volatile compounds in the resulting polymers were quantified and identified by thermogravimetic analysis (TGA) and thermal desorption followed by gas chromatography with mass spectrometric detection (TD-GC-MS), respectively. Glass transition temperatures of the resulting polymers as determined by differential scanning calorimetry (DSC) vary from 70°C to 125°C.

Latex particles of various sizes, containing a fluorescent dye and dispersed at low density in a poly(vinyl alcohol) matrix, were imaged by near-field scanning optical microscopy. The fluorescence intensity of the latex particles was studied quantitatively, by integrating the total intensity measured per particle. For all the samples, a high accuracy in determination of the fluorescence intensity could be achieved. The noticed difference in fluorescence intensity for particles of a similar size is mainly affected by the size distribution of the particles and by sample preparation. Particularly, the smaller particles (50−100 nm) show a significant difference in fluorescence intensity. This was confirmed by further study of the distribution of particle sizes by transmission electron microscopy and by examination of the correlation between the fluorescence intensity of the latex particles and their size. When the size difference is significant (e.g., when particles of 100 and 200 nm, which show a narrow size...

Charge-transfer fluorescence probes show a strong response of the intensity and wavelength positions of their spectra to solvent polarity and mobility. Such properties have been applied in the past to follow polymerization kinetics and solvent-induced effects (e.g., swelling) in polymeric materials. An important advantage of charge-transfer fluorescence probes is that they can be measured at extremely low concentrations, hence interference with the polymeric system is limited. Furthermore they report from “within,” since they are only sensitive to phenomena which occur in their immediate surroundings. In this paper it is shown that charge-transfer fluorescence probes can also be applied to study mechanical and thermal properties of polymers. The charge-transfer fluorescence probe Fluoroprobe (1-phenyl-4-[(4-cyano-1-naphthyl)methylene]piperidine) was doped into a polyether–polyester block copolymer, which was submitted to thermal and mechanical stress. The effect of strain applied to the polymers in various forms (fibers, sheets) and the effect of thermal processes (glass transition temperatures, phase transitions, melting points) are clearly reported by the changes in fluorescence intensity and wavelength of the Fluoroprobe molecule.

Cyanine-based near-i.r. fluorescent probes have been applied as labels to determine functional groups in polymeric materials. The advantage of such probes is that they can be applied to polymers which are autofluorescent or strongly coloured or to strongly scattering polymer emulsions. Two examples are discussed: the labelling of a polymer latex with aldehyde functional groups, by application of a cyanine with a hydrazide functionality, and the labelling of amino functional groups in a polyamide utilizing a cyanine label with an isothiocyanate functionality. The cyanines which have been applied absorb and fluoresce in the 650–700 nm range and in the 750–800 nm range, respectively. In addition to near-i.r. fluorescence, the cyanine dyes have strong absorption (with extinction coefficients in the order of 2 × 10 5 lmol −1 cm −1 ). It is shown that by application of reflection absorption measurements also sensitive detection of labelled functional groups can be realized. The combined application of fluorescence and reflection measurements allows for the detection of concentration and distribution of functional groups in polymeric systems down to very low levels.

A charge-transfer fluorescence molecule has been applied to study the structure of polystyrene latices and polystyrene—glycidylmethacrylate core—shell latices. Information on the composition of the latex could be obtained on the basis of the combined application of steady state and time-resolved fluorescence measurements. Time-resolved measurements were done using a frequency-domain approach; the time-resolved data were interpreted using the maximum entropy method of analysis.

Determination of benzo[a]pyrene (BaP) metabolites in urine can provide direct insight into recent exposure to BaP integrated from all uptake routes. In order to detect 3-OH BaP in human urine after exposure to BaP at the workplace, extremely sensitive methods need to be developed. In this paper, a new extraction method is presented, and two laserbased fluorescence techniques are evaluated. Using HPLC with laser-induced fluorescence detection, a detection limit of 8 ng/L was obtained. With laser-excited Shpol'skii spectrometry after chemical derivatization, 3-OH BaP could be detected at even a 0.5-ng/L concentration. In a pilot study, urine samples from coke-oven workers and from occupationally nonexposed control persons were analyzed. In the control samples, the average 3-OH BaP concentration was 8.3 ng/L; the 3-OH BaP concentrations were found to be highly correlated (r2 = 0.89) with urinary 1-OH pyrene, a widely used biomarker for polycyclic aromatic hydrocarbon (PAH) exposure. Significantly elevated 1-OH pyrene concentrations were measured in urine samples from coke-oven workers, but in most samples a corresponding increase of 3-OH BaP was not observed. Possible explanations for this discrepancy are discussed.

The practical applicability and analytical performance of laser-excited Shpol'skill spectroscopy (LESS) for the determination of benzo[a]pyrene (BaP) metabolites was studied. Quantitation of these compounds in fish bile can provide insight into the BaP uptake from a contaminated aquatic environment (blomonitoring). Chemical derivatization of hydroxylates BaP metabolites with methyl iodide (to improve the compatibility with the Shpol'skii matrix) was tested. The methylation of phenolic metabolites was rapid and quantitative, but with BaP-dihydro diol metabolites, mixtures and methylation and elimination products were formed

The ataxonomic discrimination of phytoplankton species on the basis of fluorescence data obtained by multiwavelength excitation in combination with wavelength selective detection in flow cytometry is demonstrated. The discrimination is based on differences in pigment composition between the species, which are reflected in their spectral characteristics. Classification can be done both by making use of the absolute fluorescence intensities and with fluorescence parameter ratios. The latter approach has the advantage that size-related effects and instrument fluctuations are reduced to a large extent. Photoadaptation does influence the absolute as well as the ratioed parameters that are obtained but does not impede the classification into major ataxonomic groups.

The characterisation of monomode passive polymer optical devices fabricated according to the POPCORN technology bymethods originated from electron, ion and optical spectroscopy is summarized. Impacts of observed waveguide perturbationson the optical characteristics ofthe waveguide are evaluated.In the POPCORN approach optical components for telecommunication applications are fabricated by photo-curing of liquidhalogenated (meth)acrylates which have been applied on moulded thermoplastic substrates. For tuning of waveguidematerial refractive indices with respect to the substrate refractive index frequently comonomer mixtures are used. Thepolymerisation characteristics, especially the polymerisation kinetics of individual monomers, determine the formation ofcopolymers. Therefore the unsaturation as function of UV-illumination time in the formation of halogenated homo- andcopolymers has been examined. From different suitable copolymer systems, after characterisation of their glass transitiontemperatures, their curing behaviour and their refractive indices as function of the monomer ratios, monomode waveguidesapplying PMMA substrates have been fabricated. To examine the material composition also in the 6 x 6 jtm2 waveguidesthey have been visualised by transmission electron microscopy. With this method e.g. segregation phenomena could beobserved in the waveguiding copolymer with features in the 100 nm range. Secondary ion mass spectrometry has been usedfor waveguide cross section characterisation as well. The optical losses in monomode waveguides caused by segregation andother material induced defects like micro bubbles formed as a result of shrinkage have been quantisized by return lossmeasurements. Defects causing scattering could be observed by convocal laser scanning microscopy and by conventionallight microscopy.Keywords: integrated optics, polymer waveguide, halogenated acrylates, halogenated methacrylates, convocal scanninglaser microscopy, transmission electron microscopy, SIGA, POPCORN

Time-resolved fluorescence measurements have been carried out on charge-transfer fluorescent molecules incorporated in polymeric lattices, consisting of polystyrene cores and polyglycidylmethacrylate shells, and in polymethylmethacrylate thin films. New approaches to the analysis of fluorescence lifetime data obtained for molecules in polymer matrices had to be applied, since conventional analysis methods appeared not suitable for such strongly heterogeneous systems. The polymer lattices could be characterized by application of phase- resolved fluorescence lifetime measurements followed by maximum-entropy methods for data analysis. The thin films were studied using time-correlated single photon counting fluorescence lifetime measurements and data analysis with a home-built program based on stretched exponential decays. Interactions of the fluorescent guest molecules could be established by combined fluorescence lifetime and depolarization measurements. Suggestions for further improvements in fluorescence lifetime methods for characterization of polymeric materials have been made.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Recently developed photobleachable polymers show a loss of < 0.1 dB/cm at 1300 nm and < 0.15 dB/cm at 1550 nm. Nonchromophore containing polymers show film waveguide losses of < dB/cm at 1300 nm and 1550 nm. Refractive indices in these materials can be tuned within a range of 0.05 by changing the polymer composition. Multilayers of cross-linked (solvent resistant) layers, each 2-10 microns have been deposited by multiple spinning steps. Using these multilayers, fully embedded, fiber-compatible strip waveguide structures have been created by masked bleaching of multilayers with chromophore containing corelayers. The lateral refractive index contrast is thereby tuned by changing the chromophore content of the corepolymer. Poling-induced loss has been investigated by wavelength and polarization dependent measurements of losses in films. The results indicate that this loss is due to increased scattering. Bleached channel waveguides in a poled (at 125 V/micrometers ) nonlinear optical polymer have been made showing losses of < dB/cm at 1300 nm. Rapid photodegradation at 1300 nm has been observed in stilbene containing channel waveguides. In a nitrogen atmosphere no degradation was seen. The same is true for waveguides in air at 1550 nm. This suggests the attack of the stilbene chromophores by singlet oxygen. Therefore a new generation of low-loss, linear, and nonlinear optical polymers based on singlet oxygen resistant molecules has been developed. The linear optical polymers are used for the realization of low-insertion loss (< 2 dB), digital (switch voltage 3-6 V) and efficient (switching power < mW, cross talk - 20 dB) pigtailed and packaged 1 X 2 switches. They utilize the strong thermo-optic effect in polymers. Their switching time is therefore limited to 1 ms whereas their polarization dependence is < 0.3 dB.

A new hydrazide derivative of a cyanine dye is synthesized for the chemical derivatization of aldehydes. With this red absorbing fluorophore it is possible to apply visible diode laser induced fluorescence (DIO-LIF) detection in conventional-size liquid chromatography (LC). The dye is based on CY5.3a-IA, a sulfonated dicarbocyanine with a iodoacetamido reactive group. The detection limit of n-octylaldehyde is 7 × 10−8 M, limited by the reactivity of the label. Mixtures comprised of strongly resembling aldehydes were derivatized with the label and analyzed by LC-DIO-LIF. The potential applicability in biological problems is shown by the derivatization of 4-hydroxy-2-nonenal (HNE).

High-resolution fluorescence spectroscopy may be used to obtain highly specific, vibrationally resolved spectral signatures of molecules. Two techniques are presented that both make use of low temperature, solid matrices. In Shpol'skii spectroscopy highly resolved spectra are obtained by employing n-alkanes as solvents that form neat crystalline matrices at low temperatures in which the guest molecules occupy well defined substitutional sites. Fluorescence line-narrowing spectroscopy is based on the application of selective (mostly laser-) excitation of the guest molecules. Principles and analytical applications of both techniques will be discussed. Specific attention will be paid to the determination of pyrene in bird meat by means of Shpol'skii spectroscopy and to the possibilities of applying two-dimensional fluorescence line-narrowing spectroscopy.