Energy acceptors

AG and AH can be expressed as a multiplicative function of hydrogen bonding in different polar and nonpolar solvents by means of enthalpy acceptor factors E - enthalpy donor factors free energy acceptor factors Q, and free energy donor factors Q (Eqs. (32) and (33), where kj, 2- 3 [kcal/mol] are regression coefficients). 

The HYBOT descriptors were successfully applied to the prediction of the partition coefficient log P (>i--octanol/water) for small organic componnds with one acceptor group from their calculated polarizabilities and the free energy acceptor factor C, as well as properties like solubility log S, the permeability of drugs (Caco-2, human skin), and for the modeling of biological activities. 

Addition of fluorescent energy acceptors such as 9,10-dibromoanthracene substantially increases chemiluminescence intensity by transferring excitation energy (132,133), as is the case with dioxetanes. 

WEE AS A van der Waals free energy acceptor surface area... 

However, cfc-stilbene does not behave as a classical triplet energy acceptor inasmuch as the rate of energy transfer is much larger than would be predicted from Eq. (9.7) for donors with triplet energies less than 57 kcal/mole. This is then additional information consistent with Eq. (9.5). 

As seen from (1) and (2), intermolecular processes may reduce essentially the lifetime and the fluorescence quantum yield. Hence, controlling the changes of these characteristics, we can monitor their occurrence and determine some characteristics of intermolecular reactions. Such processes can involve other particles, when they interact directly with the fluorophore (bimolecular reactions) or participate (as energy acceptors) in deactivation of S) state, owing to nonradiative or radiative energy transfer. Table 1 gives the main known intermolecular reactions and interactions, which can be divided into four groups ... 

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. 

A, B.. . . reactants, Px electronically excited reaction product, P reaction product in the ground state, Xx energy acceptor in electronically excited, X energy acceptor in the ground state... 

Clapp AR, Medintz IL, Fisher BR, Anderson GP, Mattoussi FI (2005) Can luminescent quantum dots be efficient energy acceptors with organic dye donors J Am Chem Soc 127 1242-1250... 

Intensive effort has been devoted to the optimization of CCP structures for improved fluorescence output of CCP-based FRET assays. The inherent optoelectronic properties of CCPs make PET one of the most detrimental processes for FRET. Before considering the parameters in the Forster equation, it is of primary concern to reduce the probability of PET. As the competition between FRET and PET is mainly determined by the energy level alignment between donor and acceptor, it can be minimized by careful choice of CCP and C. A series of cationic poly(fluorene-co-phenylene) (PFP) derivatives (IBr, 9, 10 and 11, chemical structures in Scheme 8) was synthesized to fine-tune the donor/acceptor energy levels for improved FRET [70]. FI or Tex Red (TR) labeled ssDNAg (5 -ATC TTG ACT ATG TGG GTG CT-3 ) were chosen as the energy acceptor. The emission spectra of IBr, 9, 10 and 11 are similar in shape with emission maxima at 415, 410, 414 and 410 nm, respectively. The overlap between the emission of these polymers and the absorption of FI or TR is thus similar. Their electrochemical properties were determined by cyclic voltammetry experiments. The calculated HOMO and LUMO... 

Energy transfer. Energy acceptors can be the substrate 23 as well as suitable adsorbates. 24,25 In both cases the decay curves become nonexponential and, especially in the initial part, much steeper than the spontaneous decay. 

A proposed mechanism taking place when an excited sensitizer (HS ) interacts with an energy acceptor can be described by the key energy-transfer steps depicted in the following scheme ... 

Since phenol has an appreciable dipole moment, and no low energy acceptor orbitals, it should interact best with the donors that have the largest lone pair dipole moment — the oxygen compounds. Iodine has no dipole moment and the interaction with iodine is expected to be essentially covalent. Iodine should interact best with the donors that have the lowest ionization potential, i.e., the ones whose charge clouds are most easily polarized. Similar considerations have been employed to explain the donor strengths of primary, secondary and tertiary amines 35a) and the acid strengths of (35b) ICl, Bt2, I2. CeHsOH and SO2. 

Reactions involving electron transfer. Reaction of free ion radicals, oxidation of anion radicals of aromatic and heteroaromatic hydrocarbons. Usually an energy acceptor is required to be present... 

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