Donor-acceptor crystal

Assume that the rectangular lattice consists of two weakly interacting segments, one of them having a nonzero value of a. This lattice may be considered as a simple correlated electron model for stacked donor-acceptor crystals. For a t2 one can use the cyclic spin permutation technique within... 

This chapter surveys unimolecular and bimolecular photochemical reactions in mixed molecular crystals and solid mixtures. Various photoreactions occurring in mixed crystals (solid solution), hydrogen-bonded cocrystals, donor-acceptor crystals, crystalline organic salts, and solid mixtures are described. In contrast to one-component crystals [2], the organic photochemistry of such multi-... 

When the intermolecular forces are relatively strong and directional, crystalline molecular compounds (crystalline molecular complexes) are formed. They have fixed stoichiometries and ordered structures. These two-component molecular crystals are also called cocrystals or maybe adduct crystals. Hydrogen-bonded cocrystals, donor-acceptor crystals (charge transfer crystals), and inclusion crystals (host-guest crystals) are examples of crystalline molecular complexes. Crystalline organic salt is a special case of hydrogen-bonded cocrystal or donor-acceptor crystal, i.e., proton (or electron) transfer from the acid (or donor) to base (or acceptor) occurred. 

Electrical and magnetic properties of donor-acceptor crystals (charge transfer crystals) are interesting in view of their potential applications to organic conduc-... 

The CT excitation of the 1 2 donor-acceptor crystals of various diarylacet-ylenes (DAs) with 2,6-dichlorobenzoquinone (DB) afforded quinone methide products through [2+2] cycloaddition [55]. Selected examples are displayed in Scheme 28. Although the cocrystal c was unreactive, time-resolved (ps) diffuse... 

As the above examples demonstrate, the number of photoreactive donor-acceptor crystal is now increasing. 

Fig. 1.6 The crystal structure ofthe weak donor-acceptor crystal anthracene-tetracyanobenzene (TCNB). One can clearly see how the two components alternate in parallel planes. The CN groups are indicated by a darker shade. The crystal structure is monoclinic, with a = 9.528 A, b= 12.779 A, c= 7.441 A, i8 = 92.39°.

Fig. 2.14 shows as a typical example the crystal structure of 1,4-dibromonaph-thalene. The dipole forces decrease, in contrast to the dispersive forces, only as the fourth power of the distance. Therefore, a predominant structural principle is now that in the formation of crystals, the dipole-dipole interaction be maximised. On the other hand, the tendency to closest packing remains. Weak donor-acceptor crystals, in which in the electronic ground state only a very small charge transfer occurs. 

StiU more strongly influenced by dipolar and Coulomb forces are the structures of the strong donor-acceptor crystals and the radical-ion salts. 

In some weak tt-tt donor-acceptor crystals, the acceptor lattice is ordered, while the donor has an additional degree of freedom. An example is the anthracene-tetracyano-benzene crystal (cf Fig. 1.6). Here, the donor has two equivalent sites,... 

Fig. 6.14 The anthracene-pyromellitic acid dianhydride (A-PMDA) mixed-crystal system as an example of a weak donor-acceptor crystal with mixed stacks. The ground state is neutral, nearly without charge transfer. The lowest CT state Is formed by a transition of an electron...

P. J. Strebel and Z. G. Soos, Theory of Charge Transfer in Aromatic Donor-Acceptor Crystals, J. Chem. Phys. 53, 4077-4090 (1970). 

In this paper, illustrations of some peculiar aspects of the spectroscopy of CT crystals have been given with reference to simple dimeric models. Quantitative applications of such models are only appropriate for systems with localized electron states, such as insulating ion radical salts and donor-acceptor crystals. Analysis of spectroscopic data pertaining to these systems allows an accurate determination of some fundamental interaction parameters. 

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