Time-resolved energy transfer

More recently, the method of scanning near-field optical microscopy (SNOM) has been applied to LB films of phospholipids and has revealed submicron-domain structures [55-59]. The method involves scanning a fiber-optic tip over a surface in much the same way an AFM tip is scanned over a surface. In principle, other optical experiments could be combined with the SNOM, snch as resonance energy transfer, time-resolved flnorescence, and surface plasmon resonance. It is likely that spectroscopic investigation of snbmicron domains in LB films nsing these principles will be pnrsned extensively. 

Circular polarization of luminiscence, stopped-flow fluorescence, fluorescence-monitored chemical relaxation, the evaluation of relative orientation by polarized excitation energy transfer, time-resolved fluorescent polarization ( nanosecond polarization ), and other new techniques have become valuable means for studying protein structures, their interactions and structural changes in relation to various treatments (e.g. denaturation). New fluorescent probes and quenchers have enabled the research field to expand from isolated proteins to more complicated systems such as membranes, muscle and nerve components and other subcellular structures (see also 7.3). 

Multiple detection formats, including spectral, intensity, lifetime, polarization, quenching, energy transfer, time-resolved, and phase-resolved measurements. Imaging capability with submicrometer spatial resolution. two- and three-dimensional (with eonfoeal opties) sensitive visual detection. 

Keywords Bioanalytical assays Immunoassays Lanthanide nanoparticles Luminescence resraiance energy transfer Time-resolved fluorometry... 

Keywords Nonradiative excitation energy transfer Time-resolved fluorescence anisotropy Dynamics of polymer chains ir-Conjugated polymers Single-molecule spectroscopy... 

The flnorescence dynamics imaging was carried ont by monitoring time-resolved fluorescence at 530 nm, where the rise of the tetracene fluorescence is observed, at different positions of the microcrystal. The np-converted fluorescence data were recorded every 1 pm distance. To shorten the measnrement time at each point, the up-converted signal was sampled at only fonr delay time points (- 5, 5,15, 30 ps), and then the energy transfer time, x, was evalnated by htting with the following single-exponential fnnction ... 

Both linear and nonlinear Raman spectroscopy can be combined with time-resolved detection techniques when pumping with short laser pulses [8.781. Since Raman spectroscopy allows the determination of molecular parameters from measurements of frequencies and populations of vibrational and rotational energy levels, time-resolved techniques give information on energy transfer between vibrational levels or on structural changes of short-lived intermediate species in chemical reactions. One example is the vibrational excitation of molecules in liquids and the collisional energy transfer from the excited vibrational modes into other levels or into translational energy of the collision partners. These processes proceed on picosecond to femtosecond time scales [8.77,8.79]. 

Cavanagh R R, Fleilweil E J and Stephenson J C 1994 Time-resolved measurements of energy-transfer at surfaces Surf. Sc/. 300 643-55... 

An interferometric method was first used by Porter and Topp [1, 92] to perfonn a time-resolved absorption experiment with a -switched ruby laser in the 1960s. The nonlinear crystal in the autocorrelation apparatus shown in figure B2.T2 is replaced by an absorbing sample, and then tlie transmission of the variably delayed pulse of light is measured as a fiinction of the delay This approach is known today as a pump-probe experiment the first pulse to arrive at the sample transfers (pumps) molecules to an excited energy level and the delayed pulse probes the population (and, possibly, the coherence) so prepared as a fiinction of time. 

A recent study of the vibrational-to-vibrational (V-V) energy transfer between highly-excited oxygen molecules and ozone combines laser-flash photolysis and chemical activation with detection by time-resolved LIF [ ]. Partial laser-flash photolysis at 532 mn of pure ozone in the Chappuis band produces translationally-... 

The X-ray and neutron scattering processes provide relatively direct spatial information on atomic motions via detennination of the wave vector transferred between the photon/neutron and the sample this is a Fourier transfonn relationship between wave vectors in reciprocal space and position vectors in real space. Neutrons, by virtue of the possibility of resolving their energy transfers, can also give infonnation on the time dependence of the motions involved. 

Hydrogen transfer in excited electronic states is being intensively studied with time-resolved spectroscopy. A typical scheme of electronic terms is shown in fig. 46. A vertical optical transition, induced by a picosecond laser pulse, populates the initial well of the excited Si state. The reverse optical transition, observed as the fluorescence band Fj, is accompanied by proton transfer to the second well with lower energy. This transfer is registered as the appearance of another fluorescence band, F2, with a large anti-Stokes shift. The rate constant is inferred from the time dependence of the relative intensities of these bands in dual fluorescence. The experimental data obtained by this method have been reviewed by Barbara et al. [1989]. We only quote the example of hydrogen transfer in the excited state of... 

Dendrimers with a polyphenyl core around a central biphenyl unit decorated at the rim with peryleneimide chromophores have been investigated both in bulk and at the single-molecule level in order to understand their time and space-resolved behavior [28]. The results obtained have shown that the conformational distribution plays an important role in the dynamics of the photophysical processes. Energy transfer in a series of shape-persistent polyphenylene dendrimers substituted with peryleneimide and terryleneimide chro-mophoric units (4-7) has been investigated in toluene solution [29]. 

A rather important aspeet that should be eonsidered is that interfaeial quenching of dyes does not neeessarily imply an eleetron-transfer step. Indeed, many photoehemieal reactions involving anthracene oeeur via energy transfer rather than ET [128]. A way to discern between both kinds of meehanisms is via monitoring the accumulation of photoproducts at the interfaee. Eor instance, heterogeneous quenehing of water-soluble porphyrins by TCNQ at the water-toluene interfaee showed a elear accumulation of the radical TCNQ under illumination [129]. This system was also analyzed within the framework of the exeited-state diffusion model where time-resolved absorption of the porphyrin triplet state provided a quenehing rate eonstant of the order of 92M ems. ... 

Et /ZG AG -0.2 V fluorescence quenching correlates with CT driving force no spectral overlap for energy transfer no Zs in injection site or intervening sequence k = 2 x 1011 s 1 observed up to 20 A in time-resolved and steady-state experiments shallow dependence of CT yield between 6-24 A (y = 0.2-0.3) no dependence of kci between 10-17 A strong efficiency and distance dependence of CT yield vary with Z flanking sequence and intervening mismatches... 

Hildebrandt N, Charbonniere LJ, Lohmannsroben HG (2007) Time-resolved analysis of a highly sensitive forster resonance energy transfer immunoassay using terbium complexes as donors and quantum dots as acceptors. J Biomed Biotechnol 2007 79169... 

Charbonniere LJ, Hildebrandt N, Ziessel RF, Lohmannsroben HG (2006) Lanthanides to quantum dots resonance energy transfer in time-resolved fluoro-immunoassays and luminescence microscopy. J Am Chem Soc 128 12800-12809... 

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