Strong charge-transfer complexes

Spectroscopic and Structural Consequences of the Electron Donor-Acceptor Interaction 

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HMB,NO+] complex. Indeed the unusually large slope in Fig. 10A for the [ArH, NO+] complexes is the distinguishing criterion for the existence of strong charge-transfer complexes (Flurry, 1965, 1969 Flurry and Politzer, 1969 Gur yanova et al., 1975). 

Fig. 23 The structure of the complex salt Cs2(TCNQ)3, an example of the parallel face-to-face stacking of planar TCNQ molecules in one direction which is characteristic of strong charge-transfer complexes. (After Chesnut and Arthur, 1962)...

MoeUendal, H., Grundnes, J. and Augdahl, E. (1969) Solvent effects on strong charge transfer complexes. 11. AA -Dimethylthioformamide and iodine in nonpolar and polar solvents. Acta Chem. Scand., 23, 3525-3533. 

Tetrakis(dimethylamino)ethylene (TDAE) has a strong donor ability to form strong charge-transfer complexes with electron acceptors. It has been reported that charge-transfer complex salts of fullerenes with TDAE show ferromagnetism at low temperature [5]. It was revealed that in polar solvents can be reduced in the presence of TDAE without photoirradiation (Fig. 12) [70]. From the relation between the... 

Furan and maleic anhydride undergo the Diels-Alder reaction to form the tricycHc 1 1 adduct, 7-oxabicyclo [2.2.1]hept-5-ene-2,3-dicarboxyHc anhydride (4) in exceUent yield. Other strong dienophiles also add to furan (88). Although both endo and exo isomers are formed initially, the former rapidly isomerize to the latter in solution, even at room temperature. The existence of a charge-transfer complex in the system has been demonstrated (89,90). 

First of all, the reaction pathways shown in Scheme 1 involve the formation of charge transfer complexes (CTC) between olefin and Br2- The formation of molecular complexes during olefin bromination had been hypothesized often (ref. 2), but until 1985, when we published a work on this subject (ref. 3), complexes of this type had been observed only in a very limited number of circumstances, all of which have in common a highly reduced reactivity of the olefm-halogen system, i.e. strongly deactivated olefins (ref. 4), or completely apolar solvents (ref. 5) or very low temperatures (ref 6). 

That charge-transfer effects are not involved follows from the fact that the rate of triplet decay in perfluorobenzene is larger than that in benzene. If the benzophenone triplet were to act as acceptor and the benzene derivative as donor in a charge-transfer complex, the substitution of perfluorobenzene for benzene should render this type of process much less probable due to the strongly electron-withdrawing character of the fluorine atoms. 

A relatively strong organization of an electron donor by an acceptor is typically indicated by experimental values of KEUA or KC f> > 10 M-1. For intermediate values of the formation constant, i.e., 1 < KE A < 10 m, the donor/acceptor organization is considered to be weak.17 Finally, at the limit of very weak donor/acceptor organizations with KEDA 1, the lifetime of the EDA complex can be on the order of a molecular collision these are referred to as contact charge-transfer complexes.18... 

Comparison of thermal and photochemical activation. The identical color changes that accompany the thermal and photochemical methyl transfer in various [Py+, BMe ] salts suggests that pre-equilibrium charge-transfer complexation is common to both processes. Moreover, the methyl transfer either by charge-transfer photolysis or by thermal activation of [Py+, BMeT] leads to the same products, which strongly suggests common reactive intermediates (i.e., the radical pair in equation (46)) for both thermal and photochemical processes. 

Charge-transfer complexes as intermediates in metal hydride additions to tetracyanoethylene (TCNE). Strong charge-transfer colors are observed when a colorless solution of TCNE is exposed to various metal hydrides owing to the formation of the [D, A] complex188 (equation 49). 

Double pump experiments on an organic charge transfer complex TTF-CA by Iwai and coworkers demonstrated a new class of coherent control on a strongly correlated electron-lattice system [44]. While the amplitude of the coherent oscillation increased linearly with pump fluence for single pump experiments, the amplitude in the double pump experiments with a fixed pulse interval At = T exhibited a strongly super-linear fluence dependence (Fig. 3.16). The striking difference between the single- and double-pulse results indicated a cooperative nature of the photo-induced neutral-ionic transition. 

Let us briefly mention some other binary A- B charge-transfer complexes involving neutral monomers A and B chosen rather arbitrarily from the large number of possible species of this type. These examples serve to illustrate interesting aspects of the general CT phenomenon and exhibit the strong commonality with donor-acceptor interactions considered elsewhere in this book. 

The formation of charge transfer complexes between N,N-dimethylaniline or N,N-diethylaniline and Cspectroscopic studies, also in view of their potential optical and electronic applications. Even if the spectroscopic properties of Cgo, C70 are complicated by the presence of aggregates in room temperature solutions, the emissions from the excited state charge transfer complexes between fullerenes and iVjV-dialkylani lines are strongly solvent-dependent exciplet emissions are observed in hexane, but in toluene they are absent145. 

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