Trans fluorescence spectra

Rotational Raman spectra of N2 and O2 Resonance fluorescence spectrum of Br2 Vibrational-rotational spectra of CD3H and CH3D Spectrophotometric study of stabihty of metal ion-EDTA complexes Kinetics of the H2 + I2 = 2HI reaction in the gas phase Weak-acid catalysis of BH4 decomposition Photochemistry of the cis-trans azobenzene interconversion Isotope effect on reaction-rate corrstants... 

Tsukida K, Saiki K, Takii T and Koyama Y (1982) Separation and determination of cis/lrans-P-caTOtenes by high-performance liquid chromatography. J Chromatogr 245 359-364 Wasielewski MR, Johnson DG, Bradford EG and Kispert LD (1989) Temperature dependence ofthe lowest excited singlet-state lifetime ofall-fi o/w-/8-carotene and fully deuterated all-trans-P-carotene. J Chem Phys 91 6691-6697 Watanabe J, Takahashi H, Nakahara J and Kushida T (1993) Subpicosecond dynamic Stokes shift in /3-carotene solution probed by excitation energy dependence of fluorescence spectrum. Chem Phys Lett 213 351-355 Zechmeister L (1962) Cis-trans isomeric carotenoids vitamins A and arylpolyenes. Academic Press, New York... 

The time-resolved fluorescence spectrum from ( )-ll observed 0 to 250 ps after a 316-nm laser excitation is due primarily to s-trans = 394 nm). The spectrum shifts to that of s-cis = 407 nm) in a nanosecond time scale at 58°C (Figure 10a), indicating that (s-trans) converts to (s-cis) in a one-way manner (Scheme 12). Decrease of temperature retards the conversion, and finally at — 90°C in toluene no spectral change occurs at all, due to complete suppression of the conversion (Figure 10b). The (s-trans) - (s-cis) conversion proceeds with an activation energy of... 

A solution of the high-cis polymer fluoresces when excited by irradiation at 330 nm. The initial spectrum displays a weak emission at about 370 nm attributed to 2% of tra s-stilbene segments originally present in the chains. With continued irradiation (2 min) there is an increase in the emission from this band as more trans double bonds are generated, and a new emission appears at 445-500 nm. After further irradiation, this intense red-shifted luminescence becomes the predominant feature before the polymer precipitates. In a statistical copolymer of 9% of 71 and 91% of norbomene, the units of 72 are isolated between norbomene units, and the fluorescence spectrum is confined to the shorter wavelength region with a maximum around 360 nm (Miao 1994a). 

Studies of solvent polar effects on the fluorescence spectrum of immobilized stilbenes indicated that the maximum wavelength of the fluorescence emission is not very sensitive to solvent polarity. The apparent local polarity of the medium in the vicinity of the stilbene label was estimated. The trans-cis photoisomerization kinetics of the stilbene derivatives in the immobilized and free state in a medium with different viscosity was monitored by fluorescence technique at constant illumination conditions. Investigation of the microviscosity effect on the photoisomerization of the immobilized and free stilbene label was carried out by changing the relative concentration of glycerin in a glycerin-water mixture used as a solvent. With an appropriate calibration, the microviscosity in the vicinity of the stilbene label was estimated. The apparent photoisomerization rate constant of the process was found to be 3-4 times less for the immobilized label than in a free state. 

Emission inner filter effect (self-absorption) The fluorescence photons emitted in the region overlapping the absorption spectrum can be absorbed (radiative energy trans-... 

Following the initial observation113 of excimer fluorescence from dissolved polystyrene, Hirayama114 has reported a systematic survey of the fluorescence spectra of the di- and triphenylalkanes shown in Figure 14. In addition to the normal molecular spectrum of the phenyl group exhibited by all the molecules listed, an excimer band is exhibited by those systems in which the planar phenyl groups are separated by exactly three carbon atoms or a distance of 2.54 A in the trans propane chain. Since there is no evidence of a... 

Spectra have been recorded of the following polymers Poly isobutylene. Schaufele has reported a spectrum of a non-turbid specimen of this material complete with depolarization data (18). Bands at Av - 2919 and 720 cm 1 are clearly polarized and must result from symmetrical modes. Schaufele was also able to show that the short chain hydrocarbon CH3(CH2)12CH3 could be examined satisfactorily but the results were very much sharpened by cooling to liquid air temperatures. Polyisoprene and Polybutadiene. Both of these in the cis form have also been examined at Southampton very recently. The trans isomers gave no spectra due to fluorescence but no interpretation has been attempted as yet. Spectra are shown in Fig. 7 and 8. 

The phase dependent continuum excitation has been observed by Tran et al.6 and more clearly by Story and Cooke.10 They excited the Ba 6sl9d D2 states to the region of the 6p1/2 limit and observed the fluorescence from the excited 6p1/2 state of Ba+. The resulting spectrum is shown in Fig. 21.9. Using this technique they do not detect excitation below the 6p1/2 limit at all efficiently, but are able to see the variations in the cross section above the 6p1/2 limit with remarkable clarity. 

Most current interest in u.v. spectra is concerned with retinal and its cis-trans isomers. Studies at 77 K include theoretical calculations, fluorescence, and the effect of protonation on the corresponding Schiff base. The singlet-triplet absorption spectrum of all-trans-retinol has been measured. Calculations on the absorption-emission spectra of rhodopsin suggest that there is little dependence on the angular twist in the polyene chain. Pulse radiolysis has made it... 

Another example of intramolecular CT complex formation is provided by trans-4-dimethvlamino-4 -(1-oxobutvl)stilbene Solvent effects on the spectrum give a value of 22D for the excited state dipole moment. The effect of electric field on the fluorescence of 4-(9-anthry1)-N.N.-2.3,5,G-hexamethy1-aniline shows this compound forms an excited state whose dipole moment does not change with solvent . Chiral discrimination in exciplex formation between 1-dipyrenylamine and chiral amines is very weak . In the probe molecule PRODAN (6-propionyl)-2-(dimethylamino)—naphthalene the initially formed excited state converts to a lower CT state as directly evidenced by time-resolved spectra in n-butanol. Rate constants for intramolecular electron transfer have been measured in both singlet and triplet states of covalently porphyrin-amide-quinone molecules . Intramolecular excimer formation occurs during the lifetime of the excited state of bis-(naphthalene)hydrazides which are used as photochemical deactivators of metals in polyethylene . ... 

Absorption and fluorescence of the photoproducts, irradiation of SAA and SAT with ultraviolet light In solid solutions produces a new absorption band with a maximum at 21,300 cm l (5,49,53,55,59). The 0-0 peak of this transition has been found at 17,550 cm l in a crystalline dibenzyl matrix at 4°K (53). The extreme sharpness of this spectrum, not expected for Internally hydrogen-bonded molecules. Is an Indication of the trans-gulnold nature of the photoproduct (53). 

Aqueous acidic solutions of either stilbazolium cation exhibit only "monomer" absorption and fluorescence at concentrations of 0.005M or lower. Increasing the stilbazolium concentration in aqueous HCI (0.1-1.0M) to 0.01 M or higher results in a red-shifted, broadened and structureless "excimer" fluorescence and a slightly broadened absorption spectrum (Table 1). Irradiation of these concentrated stilbazolium solutions result in a decrease in the trans- cis isomerization and the formation of the a dimer as the principle photoproduct for both cations (Tables 2 and 3). Although both the cis isomer and the a dimer are formed from each cation in the concentrated homogeneous solution, only the 5 dimer forms from cation 1 while the p dimer and small amounts of the e dimer form from cation 2. 

Figure 34. Time-resolved fluorescence and dispersed fluorescence spectra for v, excitation of the gauche and trans conformers of propylaniline. An asterisk marks the excitation frequency in each spectrum, while an arrow indicates the detection frequency associated with the decay at left. For the trans species, complementary build-ups at different detection wavelengths were observed. For the gauche species, the Fourier transform of the decay is very rich.

Figure 35. Time-gated dispersed fluorescence spectra for V excitation of trans-propylaniline. The time ranges are as indicated. The top spectrum is the result of 12 scans, the bottom of 20 scans.

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