Charge-transfer molecules

Figure 2. Origin of the nonlinearity of charge-transfer molecules for a two-level-like disubstituted aromatic molecule. The donor (D) and acceptor (A) cooperate to distort the linear response (dotted lines) of a nonsubstituted benzene ring (below).

In the case of a charge transfer molecule such as paranltro-anlllne, only two electronic states contribute significantly in the visible range. The rest of the spectrum contributes a small, If not negligible, additive background. In the latter case, p reduces to ... 

One of the most important class of excited state charge transfer molecules is the alkyloaminonaphthalenesulfonates, which have been employed by Kosower and Huppert to make some of the early observations of the role of solvation dynamics in fast charge transfer reactions. As stated previously compounds in this class have been reviewed recently [4]. 

Second-Harmonic Generation from Non-dipolar Non-centrosymmetric Aromatic Charge-Transfer Molecules... 

Compounds 268a and 269a showed large Stokes shifts in polar solvents. Such large Stokes shifts have been observed in many TICT (twisted intramolecular charge transfer) molecules. Fluorescence decay time measurement indicated that there were two kinds of excited states, fast and slower decaying components, and the latter was the emission from the more polar state. 

Recent theoretical work on two-dimensional charge transfer molecules containing cumulene moieties indicate that just as in the case of the real part of the third-order susceptibilities (see Sect. 4.3) two-dimensionality can also increase the imaginary part [89] and lead to large two-photon absorption in the visible spectral region (Fig. 30). Donor-acceptor substituents further increase <5 in the visible range. 

Foster, R. (1969). Organic charge transfer molecules. Academic Press, London. [153] Foxman, B. M., Goldberg, P. L. and Mazurek, H. (1981). Confrontational polymorphism of Ni(NCS)2[P(CH)2CH2CN)3]2. Crystallographic study of three polymorphs. J. Inorg. Chem., 20,4368-75. [163]... 

In most cases, for charge transfer molecules, only a single major non-zero tensor component can be assumed. Then, Eq. (19) finally reduces to Eq. (20). 

The total-intensity hyper-Rayleigh scattering experiment basically consists of measuring the amount of incoherently scattered optical second harmonic (parallel and perpendicular output polarizations) versus a reference. When only this single measurement is done, only one independent tensor component can be obtained. For charge transfer molecules, this is generally approximated by P. The depolariza-... 

Shin, D.-M., and Whitten, D. G. (1988). Solvent induced mechanism change in charge-transfer molecules. Inversion versus rotation paths for the Z E isomerization of donor-acceptor substituted azobenzenes. /. Am. Chem. Soc. 100, 5206-5208. 

Mendis and de Silva111 have investigated a class of novel charge transfer molecules (II) using the semi-empirical MOPAC6.0/AM1 method. Large values of the static / are found which depend critically on the twist angle -1234. 

Thus, in this technique one measures only the vector part of As already mentioned, in the case of charge-transfer molecules under consideration here, the component is strongly enhanced and the other components intervening in Eq. (5) are negligible. 

Therefore, prediction of the p values for a given chemical structure is essential in the second-order NLO field in order to prepare appropriate systems for a specific application and constitutes the basis for the optimization of the microscopic NLO performance. The most widely used theoretical model to discuss the NLO performance of organic molecules consists of a summation over the electronic states of the system (SOS sum over states). The general SOS expressions for the components of the p tensors are well-known [30]. In many cases, only a few electronic levels contribute significantly to the NLO response and the general expressions simplify. For ID charge-transfer molecules (such as p-nitroaniline) a two-level model has yielded satisfactory results for the quadratic hyperpolarizability. For planar (2D) systems, as most phthalocyanines and analogous compounds, three... 

The primary quantum conversion act of photosynthesis in chemical terms is an ionization occurring in a charge transfer complex (28). But this cannot occur in isolated charge transfer molecules in solution or in a homogeneous single phase crystal because the products cannot escape from each other. The primary quantum conversion act as it occurs in modern photosynthesis can only take place in a laminated structure where the electrons and holes can escape from each other by electron migrations and not by atomic migrations (74). (For a discussion of the evolution of photosynthetic mechanisms, see Calvin, 74). 

These compounds are so-called charge-transfer molecules having the general structure shown in Chart 3.2. 

Chart 3.2 General structure of charge-transfer molecules (AttD molecules). 

Both the electronic and the vibronic contributions to one- and two-photon absorption of a D-it-D charge transfer molecule (4-dimethylamino-4 -Me-tra s-stilbene) were studied by density functional response theory combined with a linear coupling mode (Figure 3.8) [18]. 

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