Emission time-resolved

All systems were probed in steady-state fluorescence, absorption and time resolved emission lifetime studies at room temperature. Additionally, time resolved femtosecond transient absorption and nanosecond laser flash photolysis measurements were carried out. 

The following experimental setups and instruments were used for the various photophysical techniques. 

All UV/vis spectra were recorded on a Varian Cary 50 Scan spectrophotometer and a PERKIN ELMER UV/vis Spectrometer Lambda 2 (double beam) in solution. Absorption maxima Xmax are given in nm. 0.4 cm quartz cuvettes were used for all measurements. 

Fluorescence lifetimes were measured with a Laser Strobe Fluorescence Lifetime Spectrometer (Photon Technology International) with 337 nm laser pulses 

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Ware WR, Lee SK, Brant GJ, Chow PP (1970) Nanosecond time-resolved emission spectroscopy spectral shifts due to solvent-solute relaxation. J Chem Phys 54 4729 1737... 

Naik LR, Naik AB, Pal H (2009) Steady-state and time-resolved emission studies of thioflavin-T. J Photochem Photobiol A Chem 204 161-167... 

Jaye AA, Stoner-Ma D, Matousek P, Towrie M, Tonge PJ, Meech SR (2005) Time resolved emission spectra of green fluorescent protein. Photochem Photobiol 82 373-379... 

Rurack K, Resch-Genger U, Rettig W (1998) Global analysis of time-resolved emission - a powerful tool for the analytical discrimination of chemically similar Zn11 and Cd11 complexes. J Photochem Photobiol A 118 143-149... 

Time-resolved emission anisotropy measurements are more straightforward in pulse fluorometry. 

Ware W. R., Lee S. K., Brant G. J. and Chow P. P. (1971) Nanosecond Time-Resolved Emission Spectroscopy Spectral Shifts due to Solvent-Excited Solute Relaxation, J. Chem. Phys. 54, 4729-4737. 

Fluorescence polarization 1) steady state 2) time-resolved emission anisotropy rotational diffusion of the whole probe simple technique but Perrin s Law often not valid sophisticated technique but very powerful also provides order parameters... 

Time-resolved emission anisotropy experiments provide information not only on the fluidity via the correlation time rc, but also on the order of the medium via the ratio rco/ro. The theoretical aspects are presented in Section 5.5.2, with special attention to the wobble-in-cone model (Kinosita et al., 1977 Lipari and Szabo, 1980). Phospholipid vesicles and natural membranes have been extensively studied by time-resolved fluorescence anisotropy. An illustration is given in Box 8.3. 

Time-resolved emission of the donor or acceptor fluorescence provides direct information on the transfer rate, without the difficulties that may result from inner filter effects. 

Steady-state and time-resolved emission anisotropy measurements also allows distinction of single molecules on the basis of their rotational correlation time. 

As an example for linear x2-fitting, we analyse time resolved emission spectra of a mixture of two components with overlapping emission spectra and similar lifetimes. 

J. H. Easter, R. P. DeToma, and L. Brand, Nanosecond time-resolved emission spectroscopy of a fluorescence probe adsorbed to L-a-egg lecithin vesicles, Biophys. J. 16, 571-583 (1976). 

Figure 1.13 The time-resolved emission spectrum of anhydrite (CaS04) at two different delay times. The scale on the emission intensity axis of (b) has been enlarged by a factor of 1000 in order to clearly observe the remaining luminescence of the Eu and ions. Excitation wavelength at 266 nm (reproduced with permission from Gaft et al., 2001).

Among other examples, time-resolved luminescence has recently been applied to the detection of different trace elements (i.e., elements in very low concentrations) in minerals. Figure 1.13 shows two time-resolved emission spectra of anhydrite (CaS04). The emission spectrum just after the excitation pulse (delay 0 ms) shows an emission band peaking at 385 nm, characteristic of Eu + ions. When the emission spectmm is taken 4 ms after the pulse, the Eu + luminescence has completely disappeared, as this luminescence has a lifetime of about 10/rs. This allows us to observe the weak emission signals of the Eu + and Sm + ions present in this mineral, which in short time intervals are masked by the En + Inminescence. The trivalent ions have larger lifetimes and their luminescence still remains in the ms delay range. 

The narrow band with two maxims at 335 and 360 nm in time-resolved emission spectra of datolite (Fig. 4.16a), with a short decay time of 30 ns is connected with Ce +. 

Steady-state and time-resolved emission spectroscopy was used to study the interaction of E. colt PNP with its specific inhibitors formycin B, FA, and A -l-methylformycin A. Complexation was found to induce tautomeric shifts <2000BBA1467>. Carbocyclic analogues of formycin A and B have been recently synthesized <2004T8233>. The synthesis utilized 417 as starting material which was converted into 418 via a multistage synthesis. The latter could be converted into the formycin analogue (Scheme 36) <2004TL8233>. 

Time-resolved emission from I2(fi3n0u+) has been studied in a static system by Abrahamson, Husain, and Wiesenfeld23 following the flash photolysis of CF3I. The basis of the mechanism giving rise to the emission may be written ... 

The time-resolved emission spectra (TRES) and fluorescence lifetimes, ti, of the fluorene derivatives were measured in liquid solutions at room temperature with a PTI QuantaMaster spectrofluorimeter with 0.1 ns temporal resolution [20]. At this resolution, all investigated fluorenes exhibited TRES which were coincident with the corresponding steady-state fluorescence spectra. As an example, TRES for compounds 3 and 11 in hexane, THE, and ACN are presented in Eig. 8 for different nanosecond delays 0 ns (curves 2,4,6) and 5 ns, which modeled the steady-state condition (curves 3,5,7). No differences in the fluorescence spectra for these two delays were observed, indicating that all relaxation processes in the first excited state Si are sufficiently fast for fluorene molecifles and did not exceed the time resolution of the PTI system ( 0.1 ns). 

Excitation-wavelength-dependent emission polarization studies indicate the presence of an overlapping xy polarized transition in the bluer part of the 290-315-nm range, as indicated in Fig. 5. The combination of static absorption, time-resolved emission, and emission quantum yield measurements suggests that the emitting state has the same polarization (z axis, linear), but is not the same state as that giving rise to the 362-nm absorption peak. These assignments for the 3.5-nm particles are summarized in Fig. 5. 

Figure 54. (a) The time-resolved emission spectrum of the Nd-Yb coupled ion system in Nao.5Gdo.5WO4. (b) The same system except in Calibo glass [from Refs. (166,167)). 

A further possibility is that the signals arise from hydrated electrons or base radical ions produced by monophotonic ionization of the polymers. However, the quantum yield for photoionization of adenosine is reported to be approximately the same as that of poly(A) and poly(dA) [25], It is unlikely that photoionization of the polymers can account for the signals seen here since there is no detectable signal contribution from the photoionization of single bases [4], The most compelling argument that our pump-probe experiments monitor excited-state absorption by singlet states is the fact that ps and ns decay components have been observed in previous time-resolved emission experiments on adenine multimers [23,26-28]. 

What is the advantage of a time-resolved emission measurement with Eu3+ versus measurement of fluorescence from organic chromophores ... 

Figure 7. Flow chart summarizing the steps needed to produce time-resolved emission profiles at different wavenumbers from the raw data, the time-resolved emission profiles as a function of path difference.

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