Nonradiative excitation energy transfer

The next group of bimolecular interactions (3) shown in Table 1, includes noncontact interactions, in which fluorescence quenching occurs due to radiative and nonradiative excitation energy transfer [1, 2, 13, 25, 26]. Energy transfer from an excited molecule (donor) to another molecule (acceptor), which is chemically different and is not in contact with the donor, may be presented according to the scheme ... 

Amir D, Haas E. Estimation of intramolecular distance distributions in bovine pancreatic trypsin-inhibitor by site-specific la- 167. beling and nonradiative excitation energy-transfer measurements. Biochemistry 1987 26 2162-2175. 

Fluorescence Quenching and Nonradiative Excitation Energy Transfer. 202... 

Nonradiative excitation energy transfer from a donor D to an acceptor A summarized in Figure 13.9 requires interactions between them. These interactions can be of the Coulombic type, or due to an orbital overlap between the two species, or be a combination of both types. Two mechanisms can explain nonradiative energy transfer in donor-acceptor systems. As is the case of electron transfer, energy transfer can also happen in cascade processes. For clarity reasons, however, we will only describe the basic theoretical background for energy dyads comprising one donor D and one acceptor A. 

Keywords Steady-state fluorescence spectra Time-resolved fluorescence decays Fluorescence anisotropy Huorescence quenching Nonradiative excitation energy transfer Solvent relaxation Excimer J and H aggregates... 

The excitation (absorption of a photon) and the red-shifted emission are two distinct events that are separated by a time window ranging from units to hundreds of nanoseconds depending on the fluorophore and the host system. This enables monitoring fast kinetics, because a number of molecular processes proceed on this timescale in small volumes delimited by distances comparable with the range of intermolecular interactions and affect the time-dependent emission characteristics. They include translational and rotational diffusion of the fluorophore, reorientation of molecules in the solvation shell, segmental dynamics of flexible macromolecules, and nonradiative excitation energy transfer, etc. 

Uhlik F, Limpouchova Z, Matejicek P, Prochazka K, Tuzar Z, Webber SE (2002) Nonradiative excitation energy transfer in hydrophobically modified amphiphilic block copolymer micelles theoretical model and Monte Carlo simulations. Macromolecules 35 (25) 9497-9505. doi 10.1021/ma012073o... 

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

Amir, D. Haas, E. Determination of intramolecular distance distributions in a globular protein by nonradiative excitation energy transfer measurements. Biopolymers 1986, 25, 235-240. 

For energy transfer to occur, the energy level of the excited state of D has to be higher than that for A and the time scale of the energy transfer process must be faster than the lifetime of D. Two possible types of energy transfers are known—namely, radiative and nonradiative (radiationless) energy transfer. 

Nonradiative relaxation from states can be effected via fluorescence resonance energy transfer. The rate of energy transfer in donor-acceptor pairs is directly related to their distance, which can of course be affected by analyte complexation. Excitation energy transfer leads to quenching of the donor, but also to enhancement of the acceptor fluorescence therefore, the ratio of fluorescence intensities at donor and acceptor emission wavelengths provides information on complexation via changes in donor-acceptor distance. The chapters by Valeur, Bouas-Laurent, and Krafft describe uses of the energy transfer mechanism. 

Excited energy transfer among chromophores is one of the most ftmdamental photophysical processes. According to the mechanism the excited energy transfer is classified into 1.) radiative trivial type, 2.) nonradiative Forster type [286], and 3.) nonradiative Dexter type [285]. 

All glass lasers developed to date have used a rare earth as the active ion and optical pumping for excitation (Stokowski, 1982). Of these, flash-lamp-pumped neodymium glass lasers are the most frequently used and the most widely investigated. The spectroscopic data needed for estimation of the laser characteristics are usually obtained from small samples (Reisfeld and Jprgensen, 1977). The data include absorption, emission, nonradiative relaxation, energy transfer probabilities and laser cross sections. Laser operation predictions can be made from such data without actually demonstrating laser action. 

Energy Transfer. In addition to either emitting a photon or decaying nonradiatively to the ground state, an excited sensitizer ion may also transfer energy to another center either radiatively or nonradiatively, as illustrated in Figure 4. 

Nonradiative energy transfer is induced by an interaction between the state of the system, in which the sensitizer is in the excited state and the activator in the ground state, and the state in which the activator is in the excited and the sensitizer in the ground state. In the presence of radiative decay, nonradiative decay, and energy transfer the emission of radiation from a single sensitizer ion decays exponentially with time, /. 

Characterization and control of interfaces in the incompatible polymer blends were reported by Fayt et al. [23]. They used techniques such as electron microscopy, thermal transition analysis, and nonradiative energy transfer (NRET), etc. They have illustrated the exciting potentialities offered by diblock copolymers in high-performance polymer blends. 

Hart, R. C., Matthews, J. C., Hori, K., and Cormier, M. J. (1979). Renilla reniformis bioluminescence Luciferase-catalyzed production of nonradiating excited states from luciferin analogues and elucidation of the excited state species involved in energy transfer to Renilla green fluorescent protein. Biochemistry 18 2204-2210. 

Bimolecular reactions with paramagnetic species, heavy atoms, some molecules, compounds, or quantum dots refer to the first group (1). The second group (2) includes electron transfer reactions, exciplex and excimer formations, and proton transfer. To the last group (3), we ascribe the reactions, in which quenching of fluorescence occurs due to radiative and nonradiative transfer of excitation energy from the fluorescent donor to another particle - energy acceptor. 

Nonradiative transfer of excitation energy requires some interaction between donor and acceptor molecules and occurs if the emission spectrum of the donor overlaps the absorption spectrum of the acceptor, so that several vibronic transitions in the donor must have practically the same energy as the corresponding transitions in the acceptor. Such transitions are coupled, i.e., they are in resonance, and that is why the term resonance energy transfer (RET) or electronic energy transfer (EET) are often used. 

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