Introduction charge transfer

Gutmann, F. An Introduction to the Electrochemistry of Charge Transfer Complexes II 13... 

Figure 1. Some examples of luminescent probes with intramolecular charge transfer (ICT) electronic excited states. The numbers in parenthesis indicate the typical wavelengths of the excitation/emission maximums for each of them in polar media however, introduction of chemical groups in the unsubstituted molecular frame or attachment to a solid support may shift those values.

In the case of MAP, the concept of chirality was used so as to prevent centrosymmetry a chiral molecule cannot be superimposed on its image by a mirror or center of symmetry so that a crystal made only of left or right-handed molecules can accomodate neither of these symmetry elements. This use of the chirality concept ensures exclusion of a centrosymmetric structure. However as we shall see in the following, the departure of the actual structure from centrosymmetry may be only weak, resulting in limited nonlinear efficiencies. A prerequisite to the introduction of a chiral substituent in a molecule is that its location should avoid interfering with the charge-transfer process. 

Many of the processes that are familiar from ordinary electrochemistry have an analog at ITIES so these form a wide field of study. We limit ourselves to a brief introduction into a few important topics thermodynamics, double-layer properties, and charge-transfer reactions. Further details can be found in several good review articles... 

While the band position in the spectra of acylmetallocenes is close to that of the parent, above 325 m its intensity is enhanced with the introduction of the —COR. (This is in contrast to the alkylmetallocenes, whose spectra are almost identical to the parent metallocene.) Below 300 m(x, however, the intense, broad end-absorption in the spectrum of the parent metallocene is replaced by two intense peaks (for acylferrocenes these appear near 230 and 270 m j.). These are believed to be associated in part with electronic transitions of the substituent with the ring, superimposed upon metal to ring charge-transfer bands.7... 

In addition to this influence of the molecular structure, which correlates with the number and the delocalization of -electrons, steric effects resulting from the internal molecular geometry and the nature of the substituents may play an important role in intermolecular charge transfer because of the packing of adjacent molecules in the solid 80>. For instance, the observation that the introduction... 

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