Spectroscopy time-resolved emission

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... 

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. 

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). 

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>. 

One of the most spectacular observations in time-resolved emission spectroscopy is the rise and decay of molecular and excimer (or exciplex) spectra, illustrated in Figure 7.35(b). The structured molecular emission decreases immediately while the excimer emission increases up to a time of tens of ns, depending on the concentration. At longer times only the broad red-shifted excimer spectrum is observed. In Figure 7.35(b) the steady-state spectrum is shown in white this represents of course the integration of all the instantaneous spectra which can be obtained only through time-resolved spectroscopy. 

W.B. Norris H.P. Broida, Time Resolved Emission Spectroscopy in Acetylene-Oxygen Explosions , TR-33 (1969), (AD 714 730) 31) K.W. Reed L. Rudlin, Optical Spectra Produced by 13-gm Pentolite Spheres in Several Gases at Atmospheric Pressure , NOLTR-69-37 (1969), (AD 689 354) 32) D.E. Chasan G. 

LANTHANIDE AND ACTINIDE SOLUTION CHEMISTRY AS STUDIED BY TIME-RESOLVED EMISSION SPECTROSCOPY... 

Basic principles of Time-Resolved Emission Spectroscopy (TRES)... 

Fig. 1. Schematic view of the 3D experimental data collected in Time-Resolved Emission Spectroscopy.

Most of the time-resolved emission spectroscopy setups are home made in the sense that they are built from individual devices (laser, detection system,. ..) hence they are not of a plug and press type, so that their exact characteristics may vary from one installation to the other. Some of these differences have no impact on the overall capabilities of the system but some have a drastic influence on the way the collected data are processed and analysed. This aspect will be detailed in the next section, while this section deals with a general description of the apparatus. The most basic type of apparatus will be described, with no reference to sophisticated techniques such as Time Correlated Single Photon Counting or Circularly Polarized Luminescence devices. 

Time-resolved emission spectroscopy is gaining importance in the study of various chemical aspects of luminescent lanthanide and actinide ions in solution. Here, the author describes the theoretical background of this analytical technique and discusses potential applications. Changes in the solution composition and/or in the metal-ion inner coordination sphere induce modifications of the spectroscopic properties of the luminescent species. Both time-resolved spectra and luminescence decays convey useful information. Several models, which are commonly used to extract physico-chemical information from the spectroscopic data, are presented and critically compared. Applications of time-resolved emission spectroscopy are numerous and range from the characterization of the... 

Lanthanide and actinide solution chemistry as studied by time-resolved emission spectroscopy 465... 

The relaxation time for this new dynamic equilibrium varies from femtoseconds to picoseconds. The fast reorientation of solvent molecules causes a fast solva-tochromic shift in the fluorescence band of the organic chromophores. Solvation dynamics is measured in terms of (8v (0) 8v (/)), where the fluctuating frequency v(t) is the difference in solvation energies between the two electronic states involved, i.e., v(t)= sE(t)/h [110]. In time-resolved emission spectroscopy the time dependence of the excited-state distribution is monitored via the frequency shift of the emission... 

The results discussed above have shown that time-resolved emission spectroscopy can provide detailed insight into vibronic deactivation paths of triplet substates, even when the zero-field splitting is one order of magnitude smaller than the obtainable spectral resolution (= 2 cm ). This is possible at low temperature (1.3 K), because the triplet sublevels emit independently. They are not in a thermal equilibrium due to the very small rates of spin-lattice relaxation between these substates. In the next section, we return to this interesting property by applying the complementary methods of ODMR and PMDR spectroscopy to the same set of triplet substates. 

The information obtained from the phosphorescence microwave double resonance (PMDR) spectroscopy nicely complements the results deduced from time-resolved emission spectroscopy. (See Sect. 3.1.4 and compare Ref. [58] to [61 ].) Both methods reveal a triplet substate selectivity with respect to the vibrational satellites observed in the emission spectrum. Interestingly, this property of an individual vibronic coupling behavior of the different triplet substates survives, even when the zero-field splitting increases due to a greater spin-orbit coupling by more than a factor of fifty, as found for Pt(2-thpy)2. 

In Sect. 4.2.7 it will be shown that the emission of the backgroimd decays also at T = 1.3 K biexponentiaUy with time constants of 600 ns and 110 ps. This is due to the fact that both states I and II are not in a fast thermal equilibrimn. By time-resolved emission spectroscopy one can separate the super-imposed emissions of the two states. Details are discussed in Sect. 4.2.8. 

In conclusion, it is possible for Pt(2-thpy)2, to separate the emission spectra that are super-imposed in time-integrated spectra by time-resolved emission spectroscopy. It is important that one also obtains a low-temperature (1.3 K) emission spectrum from a higher lying state with the corresponding high spectral resolution. This possibility is a consequence of the relatively slow spin-lattice relaxation. Or vice versa, since the monitored time-resolved emission spectra are clearly assignable to different triplet substates, these results nicely support the concept of a slow spin-lattice relaxation as developed above. Moreover, the results presented reveal even more distinctly a triplet substate selectivity with... 

Due to the slow processes of spin-lattice relaxation, an emission of a higher lying triplet substate cannot be frozen out even at very low temperature. Thus, emissions of different substates are often superimposed in the usually monitored time-integrated spectra. This fact can strongly complicate an interpretation. However, by use of the method of time-resolved emission spectroscopy, separated triplet sublevel spectra are obtained for Pd(2-thpy)2 (Fig. 8) and for Pt(2-thpy)2 (Fig. 22). Thus, a more reliable assignment of the spectra, particularly in the regions of the vibrational satellites is achieved [58,60]. 

Time-resolved emission spectroscopy (TRES), also referred to as time-resolved Stokes shift spectroscopy, enables one to derive information about the dynamics of biopolymer-solvent interactions on the femtosecond to nanosecond time scales, provided that suitable solvatochromic fluorescent probes have been identified. Such probes should exhibit significant Stokes shifts that change with solvent polarity and should have fluorescent lifetimes on the order of the dynamic solvent exchange process or longer. TRES detects solvent dynamics that influences the energy difference between the excited and the ground states of the fluorophore and is insensitive to dynamic processes that are significantly slower than the fluorescence lifetime. 

Ghiggino, K. P., Lee, A G., Meech, S. R., O Cbnnor, D. V., Phillips, D. Time-Resolved Emission Spectroscopy of the Dansyl Fluorescence Probe. BIOOHEM (in press)... 

Time-resolved emission spectroscopy has provided valuable information on the nature of excited states in polymers. Two distinct types of excimers have been observed in poly(Y-vinylcarbazole) using picosecond time-resolved fluorescence. The sandwich-type excimer emitting at 420 nm was formed in several nanoseconds, whereas a second excimer emitting at 375 nm was formed immediately after a lOps electron pulse. (Scheme 13). Similar observations were also... 

Spectroscopic characterization of the ablated plume was performed by the time resolved emission spectroscopy. The review emission spectra from plasma were recorded in the UV and visible ranges with a CCD array detector. 

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