Intensities Of Vibronic Bands Research Articles

Vibronic absorption spectra of the angular fused bisindolo- and biscarbazoloanthracene blue fluorophores for OLED applications

An in-depth analysis of the vibronic absorption spectra for the recently synthesized blue-fluorescent OLED emitters bis[(1,2)(5,6)]indoloanthracene and biscarbazolo[3,4-a:3′,4′-h]anthracene has been carried out computationally at the density functional theory level within the Franck-Condon approximation. These molecules are characterized by extended and rich electronic absorption spectra with most absorption bands being of vibronic origin. The first excited singlet state of bis[(1,2)(5,6)]indoloanthracene compound demonstrates a clear observable double-peak vibronic progression for two different active modes in the absorption spectrum, while the S2 state is vibronically inactive. In contrast, for the larger biscarbazolo[3,4-a:3′,4′-h]anthracene compound the S0 → S2 transition demonstrates well-resolved intense vibronic bands which overlap the less intense progressions of few modes in the S0 → S1 transition. We have also found, that even the higher-lying and very intense S0 → S4 and S0 → S5 transitions for bis[(1,2)(5,6)]indoloanthracene and biscarbazolo[3,4-a:3′,4′-h]anthracene, respectively, are characterized by clear vibronic progressions in excellent agreement with experimental spectra.

Effects of terthiophene as the end-groups in triblock copolymers consisting of poly(fluorene vinylene) and oligo(phenylene vinylene): Time-resolved fluorescence and its anisotropy

Effects of terthiophene (3T) as the end-groups in poly(9,9-di-n-octyl-fluorene-2,7-vinylene)s (PFVs) were studied by means of time-resolved fluorescence and anisotropy techniques. In a terthiophene end-modified triblock copolymer consisting PFV and oligo(phenylene vinylene) (PV, as the middle segment), [(10PFV)2-7PV](3T)2, steady-state fluorescence spectrum shows much intense vibronic bands compared to those of the reference copolymer without terthiophene groups. In contrast, the absorption spectrum of [(10PFV)2-7PV](3T)2 was almost identical to that of the reference copolymer. Fluorescence quantum yield of the 3T end-modified polymer is significantly lower than that of the reference copolymer: ϕf = 0.62 vs 0.83. It was found that fluorescence spectral profile of [(10PFV)2-7PV](3T)2 is time-dependent: As the delay time increases, relative intensities of the higher vibronic bands increase. Time-resolved signals were analyzed by two decay components, 430 ps (shorter wavelength region) and 630 ps (longer wavelength region). On the other hand, fluorescence anisotropy ratios decrease as the monitored wavelength becomes longer. It is highly likely that the terthiophene end-modified copolymer undergoes structural change in the excited state. The longer decay component can be ascribed to a species of which π-system of the excited PFV part is expanded over the end-group after coplanarization of the terthiophene unit upon the excitation.

The excited-state structure, vibrations, lifetimes, and nonradiative dynamics of jet-cooled 1-methylcytosine

We have investigated the S0 → S1 UV vibronic spectrum and time-resolved S1 state dynamics of jet-cooled amino-keto 1-methylcytosine (1MCyt) using two-color resonant two-photon ionization, UV/UV holeburning and depletion spectroscopies, as well as nanosecond and picosecond time-resolved pump/delayed ionization measurements. The experimental study is complemented with spin-component-scaled second-order coupled-cluster and multistate complete active space second order perturbation ab initio calculations. Above the weak electronic origin of 1MCyt at 31 852 cm-1 about 20 intense vibronic bands are observed. These are interpreted as methyl group torsional transitions coupled to out-of-plane ring vibrations, in agreement with the methyl group rotation and out-of-plane distortions upon 1ππ∗ excitation predicted by the calculations. The methyl torsion and ν1' (butterfly) vibrations are strongly coupled, in the S1 state. The S0 → S1 vibronic spectrum breaks off at a vibrational excess energy Eexc ∼ 500 cm-1, indicating that a barrier in front of the ethylene-type S1⇝S0 conical intersection is exceeded, which is calculated to lie at Eexc = 366 cm-1. The S1⇝S0 internal conversion rate constant increases from kIC = 2 ⋅ 109 s-1 near the S1(v = 0) level to 1 ⋅ 1011 s-1 at Eexc = 516 cm-1. The 1ππ∗ state of 1MCyt also relaxes into the lower-lying triplet T1 (3ππ∗) state by intersystem crossing (ISC); the calculated spin-orbit coupling (SOC) value is 2.4 cm-1. The ISC rate constant is 10-100 times lower than kIC; it increases from kISC = 2 ⋅ 108 s-1 near S1(v = 0) to kISC = 2 ⋅ 109 s-1 at Eexc = 516 cm-1. The T1 state energy is determined from the onset of the time-delayed photoionization efficiency curve as 25 600 ± 500 cm-1. The T2 (3nπ∗) state lies >1500 cm-1 above S1(v = 0), so S1⇝T2 ISC cannot occur, despite the large SOC parameter of 10.6 cm-1. An upper limit to the adiabatic ionization energy of 1MCyt is determined as 8.41 ± 0.02 eV. Compared to cytosine, methyl substitution at N1 lowers the adiabatic ionization energy by ≥0.32 eV and leads to a much higher density of vibronic bands in the S0 → S1 spectrum. The effect of methylation on the radiationless decay to S0 and ISC to T1 is small, as shown by the similar break-off of the spectrum and the similar computed mechanisms.

Dispersed-fluorescence spectroscopy of jet-cooled calcium ethoxide radical (CaOC2H5)

Dispersed fluorescence (DF) spectra of the calcium ethoxide radical (CaOC2H5) have been obtained by pumping the Ã12A′←X̃2A′ and the Ã22A′′←X̃2A′ origin bands in its laser-induced fluorescence spectrum. Dominant transitions in the vibrationally resolved DF spectra are well reproduced using Franck-Condon factors predicted by complete active space self-consistent field (CASSCF) calculations. Collision-induced population transfer between the Ã12A′and the A22A′′ states results in additional peaks in the experimental DF spectra. Differences between the intensities of vibronic bands in the Ã12A′→X̃2A′ and the Ã22A′′→X̃2A′ DF spectra are attributed to different symmetries of the two excited electronic states.

DFT simulation of the heteroannelated octatetraenes vibronic spectra with the Franck–Condon and Herzberg–Teller approaches including Duschinsky effect

Calculations of vibronic structure in the electronic absorption spectra are carried out for the series of heteroannelated octatetraenes on the basis of density functional theory method. Both Franck–Condon and Herzberg–Teller approaches have been used for estimation of frequency and intensity of vibronic bands in the simulated absorption spectra with respect to the S0→S1 electronic transition. The key result discussed in this work is that the electronic transition into the first singlet excited states is vibronically-active in the absorption spectra for all studied circulenes in a good agreement with experimental observations. We have confirmed our previous assumption that the first (low-lying) weak absorption maximum in the spectra of tetra-tert-butyltetraoxa[8]circulene and dithieno[3,4-b:3′,4′-d]thiophene-annelated cyclooctatetraene can be assigned just for the S0→S1 transition which produce the next more intense vibronic satellite. In the case of aza[8]circulenes the S0→S1 transition is symmetry allowed and the corresponding vibronic bands are less intense relative to 0–0 band.

The laser-induced fluorescence spectroscopy of yttrium monosulfide

We have investigated the laser-induced fluorescence (LIF) excitation spectra and dispersed fluorescence (DF) spectra of yttrium monosulfide (YS) in the energy range of 17860–20700cm−1. Rotational analyses indicated that almost all of the intense vibronic bands can be attributed to the new [19.38]2Σ+(υ′)-X2Σ+(υ″) transition system. The missing (1, 2), (2, 1) and (3, 3) bands are caused by their very small Franck–Condon factors, as confirmed by our calculations. The new 2Σ+ state has been suggested to arise from the electronic configuration of (core)1σ22σ21π33σ2π, featuring a charge-transfer nature. Moreover, the spin-rotation parameter γ for the newly observed 2Σ+ state has been determined to be 0.0206cm−1, the magnitude of which is larger than the known γ(X2Σ+) (0.001427cm−1) but smaller than γ(B2Σ+) (−0.1515cm−1).

Aqueous Dispersion and Temperature Induced Reversible Fluorescence Properties of 1-Pyrenecarboxaldehyde

The fluorescence intensities for various vibronic fine structures in the 1-pyrenecarboxaldehyde (PyCHO) fluorescence show strong environment dependence. In aqueous solvent, the distribution of dye is highly depended on its concentration labels and varies from excimer to monomeric state. UV-Vis Spectroscopic analysis could not able to detect dye below 10-7M concentration, whereas a new monomeric peak at 342 nm was observed after heating and cooling treatment at above the concentration. At 10-8M concentration, only monomeric distribution of 1-PyCHO reveals a strong temperature (20-50 °C) induced reversible perturbation of the vibronic band intensities. This suggests the operation of some specific solute-solvent dipole-dipole interaction mechanism strongly influenced by heating.

Cavity Ringdown Spectroscopy of the Hydroxy-Methyl-Peroxy Radical

We report vibrational and electronic spectra of the hydroxy-methyl-peroxy radical (HOCH2OO(•) or HMP), which was formed as the primary product of the reaction of the hydroperoxy radical, HO2(•), and formaldehyde, HCHO. The ν1 vibrational (OH stretch) spectrum and the à ← X̃ electronic spectrum of HMP were detected by infrared cavity ringdown spectroscopy (IR-CRDS), and assignments were verified with density functional calculations. The HMP radical was generated in reactions of HCHO with HO2(•). Free radical reactions were initiated by pulsed laser photolysis (PLP) of Cl2 in the presence of HCHO and O2 in a flow reactor at 300-330 Torr and 295 K. IR-CRDS spectra were measured in mid-IR and near-IR regions over the ranges 3525-3700 cm(-1) (ν1) and 7250-7800 cm(-1) (à ← X̃) respectively, at a delay time 100 μs after photolysis. The ν1 spectrum had an origin at 3622 cm(-1) and exhibited partially resolved P- and R-branch contours and a small Q-branch. At these short delay times, spectral interference from HOOH and HCOOH was minimal and could be subtracted. From B3LYP/6-31+G(d,p) calculations, we found that the anharmonic vibrational frequency and band contour predicted for the lowest energy conformer, HMP-A, were in good agreement with the observed spectrum. In the near-IR, we observed four well spaced vibronic bands, each with partially resolved rotational contours. We assigned the apparent origin of the à ← X̃ electronic spectrum of HMP at 7389 cm(-1) and two bands to the blue to a progression in ν15', the lowest torsional mode of the à state (ν15' = 171 cm(-1)). The band furthest to the red was assigned as a hot band in ν15″, leading to a ground state torsional frequency of (ν15″ = 122 cm(-1)). We simulated the spectrum using second order vibrational perturbation theory (VPT2) with B3LYP/6-31+G(d,p) calculations at the minimum energy geometries of the HMP-A conformer on the X̃ and à states. The predictions of the electronic origin frequency, torsional frequencies, anharmonicities, and rotational band contours matched the observed spectrum. We investigated the torsional modes more explicitly by computing potential energy surfaces of HMP as a function of the two dihedral angles τHOCO and τOOCO. Wave functions and energy levels were calculated on the basis of this potential surface; these results were used to calculate the Franck-Condon factors, which reproduced the vibronic band intensities in the observed electronic spectrum. The transitions that we observed all involved states with wave functions localized on the minimum energy conformer, HMP-A. Our calculations indicated that the observed near-IR spectrum was that of the lowest energy X̃ state conformer HMP-A, but that this conformer is not the lowest energy conformer in the à state, which remains unobserved. We estimated that the energy of this lowest conformer (HMP-B) of the à state is E0 (Ã, HMP-B) ≈ 7200 cm(-1), on the basis of the energy difference E0(HMP-B) - E0(HMP-A) on the à state computed at the B3LYP/6-31+G(d,p) level.

Aqueous Dispersion and Temperature Induced Reversible Fluorescence Properties of 1-Pyrenecarboxaldehyde

The fluorescence intensities for various vibronic fine structures in the 1-pyrenecarboxaldehyde (PyCHO) fluorescence show strong environment dependence. In aqueous solvent, the distribution of dye is highly depended on its concentration labels and varies from excimer to monomeric state. UV-Vis Spectroscopic analysis could not able to detect dye below 10-7M concentration, whereas a new monomeric peak at 342 nm was observed after heating and cooling treatment at above the concentration. At 10-8M concentration, only monomeric distribution of 1-PyCHO reveals a strong temperature (20-50 °C) induced reversible perturbation of the vibronic band intensities. This suggests the operation of some specific solute-solvent dipole-dipole interaction mechanism strongly influenced by heating.

The Effects of Aggregation on Electronic and Optical Properties of Oligothiophene Particles

Solution processing of oligothiophene molecules is shown to produce a range of particles with distinct morphologies. Once isolated on a substrate, the optical and electronic properties of individual particles were studied. From polarized scanning confocal microscopy experiments, distinct particles that are identifiable by shape were shown to have similar emission spectra except in regard to the 0-0 vibronic band intensity. This suppression of the 0-0 vibronic band correlates to the amount of energetic disorder present in a weakly coupled H-aggregate. The studied particles ranged from moderate to almost complete suppression of the 0-0 vibronic band when compared to the emission spectrum of the isolated molecule in solution. All particles were found to have a high degree of geometric order (molecular alignment) as observed from the fluorescence dichroism (FD) values of around 0.7-0.8 for all the studied morphologies. The structural and electronic properties of the particles were investigated with Kelvin probe force microscopy (KPFM) to measure the local contact potential (LCP) difference, a quantity that is closely related to the differences in intermolecular charge distribution between the oligothiophene particles. The LCP was found to vary by as much as 70 mV between different oligothiophene particles and a trend was observed that correlated the LCP changes with the amount of energetic disorder present, as signified by the suppression of the 0-0 vibronic peak in the emission spectra. Combined polarized scanning confocal microscopy studies, along with KPFM measurements, help to provide fundamental insights into the role of morphology, molecular packing, and intermolecular charge distributions in oligiothiophene particles.

Unified Description of Optical Properties and Photostability of Fluorescent Proteins by Means of the Chromophore-Protein Electrostatic Interactions

Fluorescent proteins (FPs) are widely used in two-photon microscopy as genetically-targeted probes. Understanding the mechanisms of their two-photon absorption (2PA) and photobleaching is therefore of prime importance for creation of brighter and more photostable mutants.We study the effect of the local electrostatic environment of the FP chromophore on its optical properties and photostability. To this end, we select the series of red FPs, including DsRed and a number of its Fruits derivatives, all possessing the same red anionic chromophore but different local surrounding.2PA spectroscopy provided us a direct experimental access to the absolute values of the local electric field on the chromophore site [1]. Using crystallography data available for several of the proteins, we perform here a series of QM/MM calculations of local electric potentials and fields on the chromophore site and determine the “hot” spot on the chromophore where the calculated fields almost quantitatively match the experimental data. This procedure also allows us to validate the protonation state of certain amino acids near the chromophore.We further analyze our experimental 2PA spectra of the Fruits [2] and show that the local electric field at the “hot” spot of the chromophore drives their 2PA absorptivity. The variations of the field result in different vibronic band intensities and eventually are responsible for the 2PA (vibronic) peak amplitude.We finally present our experimental data on photobleaching kinetics and demonstrate that there is a correlation between the rate of chromophore degradation and local electrostatic potential on the chromophore.Our results suggest the directions of mutagenesis that can simultaneously improve the 2PA brightness and photostability.

Polarity Behaviour and Specific Interactions of Imidazolium-Based Ionic Liquids in Ethylene Glycol

The molecular interactions of the ionic liquids (ILs) 1-butyl-3-methylimidazolium tetrafluoroborate [C(4)mim][BF(4) ], 3-methyl-1-octylimidazolium tetrafluoroborate [C(8)mim][BF(4)] and 1-butyl-3-methylimidazolium octylsulfate [C(4)mim][C(8)OSO(3)] are investigated in ethylene glycol (EG) over the whole mole fraction range using fluorescence (steady-state and time-resolved), Fourier transform infrared and nuclear magnetic resonance (NMR) spectroscopy. The cybotactic region surrounding the pyrene fluorescent probe exhibits peculiar characteristics for different ILs in the EG-rich region. The extent of solute-solvent interactions is assessed by determining the deviations of experimentally observed vibronic band intensity ratios of peak 1 to peak 3 of pyrene fluorescence (I(1)/I(3)) from a composite I(1)/I(3) value obtained using a preferential solvation model. A distinct vibrational frequency shift for various stretching modes of EG (O−H) or ILs (C−H of ring protons, B−F and S=O of anions) indicates specific interactional preferences of EG toward the IL protons/anion. Splitting of the O−H vibration band of EG at 3000-3700 cm(-1) into three separate bands, and analysis of the changes in location and area of these bands as a function of concentration enable precise determination of the effect of ILs on hydrogen bridges of EG. NMR chemical shifts and their deviations from ideality show multiple hydrogen-bonding interactions of varying strengths between unlike molecules in the mixtures. A comparison of spectroscopic results with thermodynamic properties shows that the mixing microscopic behaviour of the investigated systems is completely different from the macroscopic behaviour, which is primarily governed by the difference in shape, size and nature of the molecules.

Thermoresponsive-fluorescent isopropylacrylamide–vinylpyridine–pyrenemethylacrylamide terpolymer and its complexation behaviour with DNA

Temperature and pH-responsive, fluorescent random terpolymer of N-isopropylacrylamide (NIPA), 4-vinylpyridine (4VP) and N-pyrenemethylacrylamide (PyMeA) was synthesized. Temperature and pH-dependent fluorescence behaviour of poly(NIPA–4VP–PyMeA) terpolymer was investigated by fluorescence spectroscopy. The protonation of terpolymer (i.e. high cationic charge) in the acidic pH region provided significantly higher values for the ratio of the first to third vibronic band intensities (I1/I3) with respect to that found for pyrene in an aqueous medium (i.e. 1.87). I1/I3 ratio significantly decreased with increasing pH depending upon the decreasing polarity of microenvironment due to the deprotonation of terpolymer. As a new potential carrier for DNA-delivery, the interaction of fluorescent poly(NIPA–4VP–PyMeA) terpolymer with DNA was investigated. The addition of DNA into the fluorescent terpolymer solution resulted in the formation of stable, colloidal terpolymer-DNA complex due to the bridge formation between phosphate groups of DNA and protonated 4VP units of the fluorescent terpolymer. The hydrodynamic diameter of DNA-poly(NIPA–4VP–PyMeA) terpolymer complex increased with increasing DNA concentration. The formation of colloidal complex particles lower than 1μm at the pHs close to the physiological pH value showed that poly(NIPA–VP–PyMeA) terpolymer could be utilized as a new fluorescent non-viral vector for DNA delivery.

Vibronic spectra of solutions and sols of copper phthalocyanine

Optical spectra of solutions and sols prepared from finely dispersed crystalline copper phthalocyanine (CuPc) were studied. The CuPc preparation was demonstrated to contain an admixture of an amorphous phase. The amorphous phase proved to be soluble in dioxane and heptane with the formation of a true molecular solution of CuPc. It was found that CuPc molecules are absorbed by polyethylene, polypropylene, polycaproamide, and cellulose triacetate films. The optical spectrum of individual CuPc molecules was demonstrated to differ substantially from those of particles of the pigment. It featured intense vibronic bands belonging to three π → π* transitions typical of aromatic structures and a series of bands characteristics of n → π* transitions involving nitrogen atoms (<29000 cm−1) but showed no absorption bands characteristic of dispersions of the pigment in the visible spectrum (400–800 cm−1). It was revealed that the Q-band (λ = 670 nm), assigned in the literature to individual CuPc molecule, in reality belongs to CuPc associates.

1,3,6,8-Tetraethynylpyrene and 1,3,6,8-tetrakis (trimethylsilylethynyl) pyrene: Photophysical properties in homogeneous media

The photophysical properties of two new tetra substituted derivatives of pyrene: 1,3,6,8-tetraethynylpyrene (TEP) and 1,3,6,8-tetrakis(trimethylsilylethynyl)pyrene (TEP-TMS) have been studied. Studies were done with respect to mirror image symmetry in the absorption and emission spectra and permissive or forbidden nature of S 0–S 1 transition, solvent sensitivity of the first and third vibronic bands and fluorescence anisotropy. Both the derivatives exhibited a strongly allowed S 0–S 1 transition, high fluorescence quantum yield, shorter fluorescence lifetime compared to pyrene and invariance of the vibronic band intensity ratio to solvent polarity. The behavior of the two pyrene derivatives validates the hypothesis “solvent polarity mediates vibronic coupling and therefore the emission band intensities, for forbidden S 0–S 1 transitions”. The trimethylsilyl derivative (TEP-TMS) was characterized by a strong fluorescence in solid state. The tetraethynyl derivative (TEP) showed high fluorescence anisotropy comparable to the well-known anisotropy probe DPH in glycerol at 0 °C. The fluorescence intensities of TEP and TEP-TMS did not show any significant change in the temperature ranger 0–40 °C for a low viscous solvent like ethanol and in the range 0–60 °C in glycerol. Unlike pyrene, no excimer emission was observed even up to 10 −3 M for TEP and TEP-TMS.

Spectroscopic characterization of the 4-hydroxy catechol estrogen quinones-derived GSH and N-acetylated Cys conjugates.

Estrogens, including the natural hormones estrone (E(1)) and estradiol (E(2)), are thought to be involved in tumor induction. Specifically, catechol estrogen quinones (CEQs) derived from the catechol estrogens 4-hydroxyestrone (4-OHE(1)) and 4-hydroxyestradiol (4-OHE(2)) react with DNA and form DNA adducts (Cavalieri, E. L., et al. (1997) Proc. Natl Acad. Sci. U.S.A. 94, 10037). CEQs are also conjugated with GSH, a reaction that prevents damage to DNA, providing biomarkers of exposure to CEQs. Current detection limits for these analytes by HPLC with multichannel electrochemical detection are in the picomole range (Devanesan, P., et al. (2001) Carcinogenesis 22, 489). To improve the detection limit of CEQ-derived conjugates, spectrophotometric monitoring was investigated. Fluorescence and/or phosphorescence spectra of the 4-OHE(1), 4-OHE(2), Cys, N-acetylcysteine (NAcCys), 4-OHE(1)-2-SG, and 4-OHE(2)-2-SG conjugates and their decomposition products 4-OHE(1)-2-NAcCys and 4-OHE(2)-2-NAcCys were obtained at 300 and 77 K. It is shown that (i) 4-OHE(1)- and 4-OHE(2)-derived SG and NAcCys conjugates are weakly fluorescent at 300 K (with the emission maximum at 332 nm) but strongly phosphorescent at 77 K; (ii) Cys and NAcCys exhibit fluorescence and phosphorescence only at 77 K; and (iii) 4-OHE(1) and 4-OHE(2) are weakly fluorescent at 300 and 77 K and not phosphorescent. The phosphorescence spectra of SG and NAcCys conjugates are characterized by a weak origin band at approximately 383 nm and two intense vibronic bands at 407 and 425 nm. After they are cooled from 300 to 77 K, the total luminescence intensity of SG and NAcCys conjugates increases by a factor of approximately 150 predominantly due to phosphorescence enhancement. Theoretical calculations revealed, in agreement with the experimental data, that the lowest singlet (S(1)) and triplet (T(1)) states of 4-OHE(2)-2-NAcCys are of n,pi* and pi,pi* character, respectively, leading to a large intersystem crossing yield and strong phosphorescence. The limit of detection (LOD) for CEQ-derived conjugates, based on phosphorescence measurements, is in the low femtomole range. The concentration LOD is approximately 10(-9) M. Therefore, we propose that capillary electrophoresis interfaced with low temperature phosphorescence detection can be used to test for human exposure to CEQs by analyzing urine.

D 1 ( 2 B 2g )→D ( 2 A u ) fluorescence from the matrix-isolated perylene cation following laser excitation into the D5(2B3g) and D2(2B3g) electronic states

Fluorescence spectra of the perylene cation, isolated in an argon matrix and pumped by direct laser excitation via the D2(2B3g)←D0(2Au) and D5(2B3g)←D0(2Au) transitions, are presented. Direct excitation into the D5 or D2 states is followed by rapid nonradiative relaxation to D1 that, in turn, relaxes radiatively. Excitation spectroscopy across the D2(2B3g)←D0(2Au) transition near 730 nm shows that site splitting plays little or no role in determining the spectral substructure in the ion spectra. Tentative assignments for ground state vibrational frequencies are made by a comparison of spectral intervals with calculated normal mode frequencies, with the strongest IR bands leading to the most intense vibronic bands.

In vivo laser-induced fluorescence detection of pyrene in nematodes and determination of pyrene binding constants for humic substances by fluorescence quenching and bioconcentration experiments.

The bioconcentration of pyrene by bacterivorous thread worms (nematodes) of the species Caenorhabditis elegans was studied with laser-induced fluorescence (LIF) spectroscopy, fluorescence imaging and a radiotracer method. The vibronic band intensities of the LIF spectra indicated that the microenvironment of pyrene in the nematodes was similar to a low-polarity solvent, and thus provided direct evidence that pyrene was accumulated in lipid-rich areas inside the nematodes. The concentration of pyrene in the nematodes was estimated from the monomer/excimer fluorescence intensity ratio. Results from this method were in fair agreement with results using 14C labeled pyrene for measuring pyrene bioconcentration. Preliminary results indicated that LIF measurements of pyrene may be possible even in single nematodes. Fluorescence microscopic observations revealed that pyrene was not adsorbed on the outside of the organisms, but was strongly concentrated in restricted areas inside the worms. In the second part of the study, the effects of six different humic substances (HS) on the bioconcentration of pyrene were investigated and sorption coefficients (KDOC) calculated from reductions in bioconcentration (KDOC(biol)) were compared with sorption coefficients measured with a fluorescence quenching technique (KDOC(flu)). The results of these two different experimental methods agreed well (with KDOC(biol) being slightly lower than KDOC(flu), indicating that the fraction of pyrene that was determined as freely dissolved by the fluorescence quenching method was comparable to the bioavailable fraction.

Molecular Interactions at Octadecylated Chromatographic Surfaces

Interactions between fluorescent solutes and an octadecylated silica surface are investigated using fluorescence emission spectra and quenching techniques under conditions similar to those found in high-performance liquid chromatography. Pyrene, benzo[a]pyrene, fluorene, biphenyl, propyldansylamide, and decyldansylamide are used as the fluorescent probes, and potassium iodide and N,N-dimethylaniline are used as quenchers. N,N-Dimethylaniline is a moderately retained quencher thought to probe deeper into the octadecylated surface than the ionic iodide salt. Solvent-dependent fluorescence emission maxima, solvent-dependent fluorescence vibronic band intensities, and quencher access to the probes are investigated using aqueous methanol mobile phase compositions ranging from 60 to 100% methanol. The resulting information is used to interpret differences in interfacial probe environments and to determine the location of the probes within the bonded phase layer. The data indicate that biphenyl and pyrene may remain in very nonpolar interfacial probe environments deep in the bonded phase layer over the mobile phase composition range tested. The fluorophore portion of both propyldansylamide and decyldansylamide may reside in an interfacial environment, which becomes more polar as the water content in the mobile phase is increased. Benzo[a]pyrene apparently becomes exposed to the mobile phase as the water content in the mobile phase increases. This is thought to be due to the relatively large size of the solute molecule and the collapse of the octadecyl chains with increased solvent polarity. Fluorene appears to interact strongly with silanol groups. The results are interpreted in light of the surface convolution and chain cluster octadecylated chromatography surface models and are found to be more constant with the chain cluster model. Implications of the results to reversed phase high-performance liquid chromatography separations are also discussed.

Collision-induced b1Σg+–a1 Δg, b1Σg+–X3 Σg- and a1Δg–X3Σg - transition probabilities in molecular oxygen

Multireference configuration interaction (MRCI) calculations have been performed for the dipole transition moments of the Noxon band, b 1 Σ g + –a 1 Δ g , and for the red and IR atmospheric emission bands, b 1 Σ g + –X 3 Σ g - and a 1 Δ g –X 3 Σ g - , in O 2 in collision complexes with different solvent molecules. The spin–orbit coupling between the b 1 Σ g + and X 3 Σ g - (M S =0) states does not change after collision so the a–X transition borrows intensity from the collision-induced Noxon band b–a, and the b–X band borrows electric dipole transition probability from the collision-induced difference dipole moments of the b and X states. The calculations show that the b–a, a–X and b–X transition probabilities are enhanced by ca. 10 5 , 10 3 and 1.2 times by O 2 +H 2 collisions. An additional order of magnitude enhancement for all three transitions is possible for solvent molecules with larger polarizability than that of molecular hydrogen. The collision-induced b–a transition dipole moment depends not only on the intermolecular distance, but also on the internuclear O–O distance. Since a–X and b–a transition moments are directly connected (D a,X =0.013iD b,a ), the strong dependence on the O 2 bond length leads to an additional enhancement of the (0,1) vibronic band intensity of the a 1 Δ g –X 3 Σ g - transition. The dipole moments of the b and X states are also shown to depend on the O 2 bond length in the collision complex, which leads to additional collision-induced enhancement of the (0,1) band of the b–X system.