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  • 1
    Electronic Resource
    Electronic Resource
    Electronic transitions in α-oligothiophene thin films. Comparison of ultraviolet/visible absorption spectroscopy and high resolution electron energy loss spectroscopy investigations (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 6344-6352 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Vapor deposited thin films of a series of α-oligothiophenes are investigated comparatively with polarized ultraviolet/visible absorption spectroscopy (UV/VIS) and by high resolution electron energy loss spectroscopy (HREELS) in specular reflection geometry. The complementary selection rules of these methods allow an assignment of the observed absorption and loss bands according to a Hückel molecular orbital model. By plotting the transition energies of corresponding bands of different members of the homologous series vs the reciprocal of the number of rings, the development of the one-dimensional "π-band-structure'' with an increasing number of rings could be followed. The extrapolation to infinite chain length leads to the electronic properties of an ideal (defect free) polythiophene. Furthermore, characteristic differences were observed in the results obtained from the two methods. The orientation of the molecules in thin films is only detectable with UV/VIS spectroscopy. It is most pronounced for α-quinquethiophene. On the other hand, HREELS gives information about the position of optical parity forbidden electronic transitions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468458
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  • 2
    Electronic Resource
    Electronic Resource
    Luminescence and photoconductivity studies on bonding, mobility and electronic deactivation in submonolayers and thin films of Distyrylbenzene
    Amsterdam : Elsevier
    Journal of Molecular Structure 267 (1992), S. 297-302 
    Details
    ISSN: 0022-2860
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0022-2860(92)87047-Y
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  • 3
    Electronic Resource
    Electronic Resource
    UV/Vis and IR spectroscopic studies on molecular orientation in ultrathin films of polythiophene model compounds
    Amsterdam : Elsevier
    Journal of Molecular Structure 293 (1993), S. 249-252 
    Details
    ISSN: 0022-2860
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0022-2860(93)80060-9
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  • 4
    Electronic Resource
    Electronic Resource
    Solvation and Solvent Relaxation in Swellable Copolymers as Studied by Time-Resolved Fluorescence Spectroscopy (2000)
    Springer
    Journal of fluorescence 10 (2000), S. 383-392 
    Details
    ISSN: 1573-4994
    Keywords: DANSyl-labeled copolymers ; swelling volume ; time-resolved fluorescence ; solvent relaxation ; rotational depolarization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The fluorescent probe dimethylaminonaphthylsulfonamide is covalently bound to the ends of the pol(ethylene glycol) chains of the swellable block copolymers poly(ethylene glycol)–polystyrene (PEG-PS) and poly(ethylene glycol)–poly(ethylene imine) (PEG-PEI) to investigate the molecular mobility inside the polymers, swollen by different liquids. Steady-state and time-resolved studies of the Stokes shift between absorption and fluorescence spectra reveal that the probe is solvated by both the polymer matrix and the liquid phase. The extent of solvation by the liquid and the mobility of the microenvironment of the probe depend on both the swelling volume of the polymer and the solubility of the probe in this liquid. Steady-state and time-resolved fluorescence depolarisation measurements show that the polymer matrix forms a very rigid solvent cage, which almost completely immobilizes the probe. Upon solvation of the probe by the liquid, the mobility of the probe increases. In PEG-PEI swollen by polar solvents, the mobilities of the probe itself and of its microenvironment, although not reaching the values observed in homogeneous solution, are significantly higher than in PEG-PS, due to the hydrophilic nature of the polymeric backbone in PEG-PEI.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1009482514437
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  • 5
    Electronic Resource
    Electronic Resource
    Fluorescence yields and molecular orientation of thin organic films: Vapor-Deposited Oligothiophenes α3T–α8T (1995)
    Springer
    Journal of fluorescence 5 (1995), S. 165-170 
    Details
    ISSN: 1573-4994
    Keywords: Thin organic films ; vapor-deposited oligothiophenes ; quantum yields
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The fluorescence quantum yields of vapor-deposited (VD) films of α-oligothiophenes,nT, with ring numbers ofn=3–8 and layer thicknesses ofd=3–50 nm were determined at room temperature andT=77 K and compared to the yields of dilute solutions and small (5T)x clusters. The yields of highly oriented ultrathin films are of the order of ΦF=5*10−5-1*10−4. The yields increase strongly with the layer thickness and also upon cooling, but do not reach the values in dilute solution. The main nonradiative deactivation step S1 → T1 in solution was quantified by1O2 production, the yields of which systematically decrease withn from ΦF (3T) to 0.36 (6T), in contrast to the fluorescence yields, which increase from ΦF=0.01 (2T) to 0.40 (6T). In films or clusters the S1 → T1 deactivation step must be a very unimportant side reaction: neither1O2 nor any signal of triplet-triplet absorption could be positively identified.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00727534
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  • 6
    Electronic Resource
    Electronic Resource
    Fluorescence Study on Translational Mobility in Polystyrene–Polyethyleneglycol Microbeads (1998)
    Springer
    Journal of fluorescence 8 (1998), S. 171-177 
    Details
    ISSN: 1573-4994
    Keywords: Polystyrene–polyethyleneglycol microbeads ; translational mobility ; dynamic excimers ; pyrenebutyric acid
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Polyethyleneglycol (PEG) chain mobility in gelatineous microbeads is investigated by means of dynamic excimer formation. Pyrenebutyric acid (PYB) is covalently linked to the chain ends as probe molecule. Excimer formation is monitored by steady-state and time-resolved fluorescence spectroscopy in the presence of a series of liquid phases and in the dry state. PYB concentration in the beads is varied over three orders of magnitude up to c = 6·10−2 M. The concentration is derived from absorption measurements in stirred bead suspensions, considering the deviations from Lambert–Beer's law in heterogeneous systems. Excimer formation is found to be a dynamic process in the presence of liquid phases which solvate both the polymer and the fluorophore. The collisional rate constant, k DM, is of the order of k DM-values of PYB in homogeneous solutions, indicating a high translational mobility. Excimer-to-monomer intensity ratios are in general accordance with the solvation capacity of the liquid phase. In the dry state excimer formation is found only at high PYB concentrations, c ≈ 3·10−2 M. It is concluded that this excimer emission arises from aggregated PYB, since corresponding fluorescence response curves show no rise time.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1022506627591
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  • 7
    Electronic Resource
    Electronic Resource
    Combined Fluorescence and NMR Studies of Reversed HPLC Stationary Phases with Different Ligand Chain Lengths (1997)
    Springer
    Journal of fluorescence 7 (1997), S. 311-315 
    Details
    ISSN: 1573-4994
    Keywords: HPLC stationary phases ; ligand length ; solid-state NMR spectroscopy ; time resolved fluorescence anisotropy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Alkyl chain bonded “reversed” HPLC phases consisting of 6 to 30 carbon atoms are investigated by fluorescence spectroscopy, steady-state and time-resolved fluorescence anisotropy, and solid-state NMR spectroscopy. The structure and dynamics of the interphase formed by alkyl chains and liquid phase penetrating each other are studied as a function of alkyl chain length. Increasing alkyl chain lengths lead to enhanced partitioning of the fluorescent probe diphenylhexatriene (DPH) into the interphase, as monitored by fluorescence decay curves. The concomitant spectral red shift of DPH fluorescence excitation maxima is evidence of increased interphase polarizability. Time-resolved fluorescence anisotropy measurements reveal that the motion of the probe molecule in the interphase is “wobble in cone”-like. Cone angles θ and rotational correlation times τR change from θ = 63° and τR = 0.75 ns in C6 phases to θ = 42° and τR = 1.50 ns in C30 phases, thus indicating decreasing probe mobility with increasing ligand length. This interpretation is supported by 13C CP/MAS NMR spectra, which show reduced contributions of alkyl chain gauche conformations, i.e., enhanced interphase order, in phases with long alkyl chains and high surface coverage. A concomitant increase in the line-widths of 1H MAS NMR peaks indicates reduced mobility of the longer chains. The spectroscopic observations are consistent with the results of HPLC separations, where enhanced shape selectivity is found with increasing ligand length, rod-shaped molecules like DPH showing the greatest increase in retention time.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1022534110945
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  • 8
    Electronic Resource
    Electronic Resource
    Investigation of Structure and Mobility of Silica Bonded Stationary Acridine Phases by Means of Fluorescence and NMR Spectroscopy (1998)
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 21 (1998), S. 11-17 
    Details
    ISSN: 0935-6304
    Keywords: Acridine-modified HPLC stationary phases ; ligand mobility ; fluorescence spectroscopy ; time-resolved fluorescence anisotropy ; solid state NMR spectroscopy ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Ligand mobility of silica-based HPLC stationary phases modified by various surface coverages of acridine-9-carboxy(N-aminoethylaminopropyl)amide ligands was investigated by fluorescence spectroscopy, time-resolved fluorescence anisotropy measurements, as well as solid-state 13C-CP/MAS- and 1H-MAS-NMR spectroscopy. Rotational correlation times, τR, of the bound acridine fluorophore obtained from fluorescence anisotropy measurements are significantly longer in the bound phase, than in solution. Also, in time-resolved experiments anisotropies do not decay to zero. These results are interpreted in terms of wobble-in-cone ligand motion. The mobility of the fluorophore in the presence of liquid phase correlates strongly with the solubility of the model compound acridine-9-carboxy-n-butylamide in the same solvent. In the good solvent acetonitrile τR = 3.2 ns is found, whereas in methanol, τR 〉 80 ns is obtained. NMR measurements of the dry phase yield large linewidths, cross polarization constants, TCH, and spin-lattice relaxation times, T1ρH, shifting around the minimum in the correlation time curve. Both fluorescence and NMR data indicate medium to low ligand mobility. No difference in the mobilities of alkyl spacer and aromatic group is observed, probably due to the rigidity of the amide group.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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