Electron-rich organic donors

Some photosensitizers, such as metal organic complexes (see also Section 6.8), can behave as either electron donors or acceptors because of their favourable redox potentials for oxidation or reduction of their excited states.670 A well-known example is tris(2,2 -bipyridine)ruthenium(II) ion ([Ru(bpy)3]2 + Scheme 6.204).10461235 When a solution of this compound is irradiated with visible light, a triplet charge-transfer excited state is formed, in which a metal-centred electron is promoted to the jt -orbital of the bipyridyl ligand [d,7t state where the metal is the electron-deficient centre (acceptor) and the ligand is the electron rich centre (donor)]. 

A large number of DTDAFs ( electron-rich olefins ) described above are very efficient donors, e.g., for their application in organic conductors however they are highly sensitive to air. Studies aimed at the preparation of such compounds, especially the aliphatic ones, have so far met with only limited success. For example, a few alkyl-substituted DTDAF derivatives could be detected electrochemically, but an attempt to isolate one of these only led to oxidation products (91JA985). Similarly, an elec-... 

Likewise, cationic acceptors afford mixed (positively) charged complexes with electron-rich donors,11 i.e., [D, A+] and anionic donors associate with electron-poor acceptors to form mixed (negatively) charged complexes,12 i.e., [D-, A]. In each case, the intermolecular (ionic) complexation or association represents the highly oriented organization of the donor/acceptor pair (independently of whether they bear positive, negative or no charge) that is often sufficient to afford crystalline complexes amenable to direct X-ray structure elucidation.13... 

Except for very electron-rich donors that yield stable, persistent radical cations, the ox values are not generally available.64 Thus the cation radicals for most organic donors are too reactive to allow the measurement of their reversible oxidation potentials in either aqueous (or most organic) solvents by the standard techniques.65 This problem is partially alleviated by the measurement of the irreversible anodic peak potentials E that are readily obtained from the linear sweep or cyclic voltammograms (CV). Since the values of E contain contributions from kinetic terms, comparison with the values of the thermodynamic E is necessarily restricted to a series of structurally related donors,66 i.e.,... 

Face-to-face aromatic stacking interactions are common in a wide range of organic charge-transfer compounds where there is a donor-acceptor interaction between an electron rich Ji-system and an electron... 

Monocyclic azines are very weak --donors and behave mainly as n-donors on interaction with electrophiles. However, 7r-donor character is significantly increased in their benzo derivatives which have higher energy HOMOs (Table 2). For example, acridine 25 forms a highly colored 1 1 molecular complex with 2,3,5,6-tetrachloro-l,4-benzoquinone (chlor-anil). Perimidine 96 is one of the strongest heterocyclic --donors and gives deeply colored molecular complexes with a variety of organic electron acceptors. This is consistent with its electron-rich structure and its separate classification. 

In the last paper on this topic [113], the same group extended this study to several different unsaturated organic compounds, leading to the conclusion that the DCA-sensitized photooxygenation of electron-rich donors is affected by solvent polarity. The chemical outcome can be connected with the fluorescence data and the formation of superoxide ion, and/or singlet oxygen proceeds from a charge-transfer complex between the donor and the acceptor upon excitation. 

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