Excited electron-donor molecule

The decay kinetics of excited electron donor molecules (the intensity of fluorescence is proportional to the concentration of excited molecules at any given time) can be interpreted in two ways. First, one may try to approxi-... 

The decay kinetics of excited electron donor molecules (the intensity of fluorescence is proportional to the concentration of excited molecules at any given time) can be interpreted in two ways. First, one may try to approximate it with the sum of two exponents, one of which refers to the decay of the fluorescence of free donor molecules and the other to that of the complex between the donor and the acceptor. This interpretation is similar to the description of the two-exponential decay of the fluorescence observed in the presence of two compounds containing heavy atoms [40]... 

A transfer of the excitation energy from the donor to the acceptor will occur when an energy acceptor molecule is placed at the proximity of an excited energy donor molecule. After energy transfer, the donor relaxes to its ground state and the acceptor is promoted to one of its excited states. A photo-induced electron transfer can be initiated after photoexcitation when an excited single electron in the LUMO of the electron donor is transferred to a vacant molecular orbital (LUMO) of the acceptor. 

In an emitter consisting of two- or more component materials, specific interactions between them must be taken into account in the formation process of excited states. Of particular interest are interactions between electron donor molecules (D) and electron acceptor molecules (A) characterized by partial or complete electron transfer from D to A. The degree of electron transfer depends on the ionization potential (Id) of the donor and the electron affinity (Aa) of the acceptor. 

Both Cgo and C70 embedded in a lipid membrane can act as efficient electron acceptors from excited electron donors adsorbed on the surface of the membrane [70]. Very interestingly, Cgo and C70 can act not only as photosensitizers for electron transfer from a donor molecule but also as mediators for electron transfer across a membrane with very high efficiencies [71],... 

It is proposed that in the presence of fluorescent probes, the energy transfer from excited carbonyl (donor molecule) to an originally unexcited acceptor molecule can take place. Because the energy of excitation of the acceptor comes from the excited donor, the donor is radiationlessly deactivated to its ground electronic state. The acceptor molecule, which has become excited at the expense of the donor, may return... 

On the other hand, in order to reduce the number of functional groups attached onto the CNT surface, a more elegant procedure involves the synthesis of SWCNTs functionalized polyamidoamide dendrimers. In this way, the extended conjugated n-system is not irreversibly perturbed and it is possible to modify further the periphery of the dendrimer with electron donor molecules to mediate the electron transfer process [131], Also in this case, the fluorescence kinetic studies brought about the existence of short-lived (0.04 0.01 ns) and long-Uved (8.6 1.2 ns) excited states. This kind of construct plays the unambiguous role of antenna system on the nanotube surface. 

Early pulse-radiolysis work in the 1960 s led to the recognition that the origin of many reactions occurring when an electron-donor molecule A in a low-polarity solvent is exposed to high-energy electrons is the ionization of excited molecules A according to Equation (5.19) ... 

Figure 6.15 Energy transfer in. solution. Deactivation of electronically excited molecules. Symbols D is excited electron-donor (singlet or triplet) A is electron-acceptor S is singlet state T is triplet state.

The study of radical ion recombination chemiluminescence of this sort emerged from observations of, so to speak, the reverse reaction. The fluorescence of aromatic hydrocarbons was found to be effectively quenched by certain electron-donor molecules, e.g. N,N-diethylaniline. A new emission appeared in such cases which exhibited a strong red shift, and was ascribed to an excited charge transfer complex ( exciplex , hetero-excimer) (see e.g. [31]), when a nonpolar solvent was used. 

In electron donor-acceptor (EDA) complexes, there is always a donor molecule and an acceptor. The donor may donate an unshared pair (an n donor) or a pair of electrons in a ti orbital of a double bond or aromatic system (a it donor). One test for the presence of an EDA complex is the electronic spectrum. These complexes generally exhibit a spectrum (called a charge-transfer spectrum) that is not the same as the sum of the spectra of the two individual molecules. Because the first excited state of the complex is relatively close in energy to the ground state, there is usually a... 

Research on the molecular basis of photoexcitation and electron transfer, including interactions of electron donor and acceptor molecules, could lead to new photochemicals. Development of model photosensitive compounds and methods of incorporating them into membranes containing donor, acceptor, or intermediate excitation transfer molecules, and... 

When both electron donor (D) and acceptor (A) groups are attached to a w-electron system it is not possible to consider the transition in terms of the excitation of one electron since it is a composite of several different one-electron excitation types. An example of a molecule which has electronic transitions of this type is Michler s ketone ... 

Porter has termed these transitions charge-transfer excitations (CT). Possible one-electron contributions to the excitation of a molecule represented as DRA (D, donor R, chromophore A, acceptor) are... 

Exciplexes are complexes of the excited fluorophore molecule (which can be electron donor or acceptor) with the solvent molecule. Like many bimolecular processes, the formation of excimers and exciplexes are diffusion controlled processes. The fluorescence of these complexes is detected at relatively high concentrations of excited species, so a sufficient number of contacts should occur during the excited state lifetime and, hence, the characteristics of the dual emission depend strongly on the temperature and viscosity of solvents. A well-known example of exciplex is an excited state complex of anthracene and /V,/V-diethylaniline resulting from the transfer of an electron from an amine molecule to an excited anthracene. Molecules of anthracene in toluene fluoresce at 400 nm with contour having vibronic structure. An addition to the same solution of diethylaniline reveals quenching of anthracene accompanied by appearance of a broad, structureless fluorescence band of the exciplex near 500 nm (Fig. 2 )... 

A number of fluorescent dyes with internal charge transfer mechanism allow the molecule to twist (rotate) between the electron donor and electron acceptor moieties of the fluorescent dipole. In most cases, the twisted conformation is energetically preferred in the excited Si state, whereas the molecule prefers a planar or near-planar conformation in the ground state. For this reason, photoexcitation induces a twisting motion, whereas relaxation to the ground state returns the molecule to the planar conformation. Moreover, the Si — So energy gap is generally smaller in the twisted conformation, and relaxation from the twisted state causes either a... 

Electron transfer (Chapter 6), considered as a photophysical process, involves a photoexcited donor molecule interacting with a ground-state acceptor molecule. An ion pair is formed, which may undergo back electron transfer, resulting in quenching of the excited donor. 

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