Excitonic coupling

K. Nakanishi and N. Harada, Circular Dichroism Spectroscopy Exciton Coupling in Organic Stereochemistry, University Science Books, Mill Vallqr, California, 1983 D. N. Kirk, Tetrahedron 42 777 (1986). 

Czader A, Bittner ER (2008) Calculations of the exciton coupling elements between DNA bases using the transition density cube method. J Chem Phys 128 035101... 

Scheme 5 shows a group of alkynylgold(i) complexes for which the studies focused on the UV-VIS electronic absorption and emission properties. Most of these compounds are of the type [(L)AuC=CR], for which the methods of synthesis have been summarized above. The products were found to show phosphorescence in various polymorphs and crystal forms of solvates. Although there are no metallophilic interactions discernible in the crystal between most of the monomers due to the steric effect of the large tertiary phosphines, there is nevertheless strong excitonic coupling based on other weak interactions, which depend on the organization of the molecules in the crystal.105,106... 

Harada, N. Nakanishi, K. Circular Dichroic Spectroscopy—Exciton Coupling in Organic Stereochemistry, Oxford University Press, Oxford, 1983. 

Exciton coupled circular dichroism (ECCD) spectra. 139... 

However, this explanation is not sufficient to accoimt for the bipha-sic CD spectrum of human ferri-protoheme—hemopexin (with 2,4-vinyl substituents), as well as the much weaker human CO-ferro-heme-hemopexin bisignate signal compared to the rabbit congener (139), and hence other factors must be involved. Several potential effectors exist (a) exciton coupling (b) the conformers produced by a 180° rotation about the a- and y-meso-carbon axis and consequent nonisometric interactions of the as5unmetric 2,4- and 9,10-substituents (c) the aromatic tryptophan residues near the heme binding site (s) and (d) two independent binding modes or sites. 

A bisignate spectrum is characteristic of exciton coupling between identical chromophores on one molecule (144), an impossibility with the 1 1 heme-hemopexin complex. Bisignate CD spectra have been observed with bilirnbin-albnmin however, bilirubin, nnlike the planar molecnle heme, can adopt an extended, helical stacked conformation... 

Hwang, I.-W. Kamada, T. Ahn, T. K. Ko, D. M. Nakamura, T. Tsuda, A. Osuka, A. Kim, D. Porphyrin boxes constructed by homochiral self-sorting assembly Optical separation, exciton coupling, and efficient excitation energy migration. J. Am. Chem. Soc. 2004,126, 16187-16198. 

In the dimer, the exciton coupling results in a fast relaxation to the S manifold. 

Soret band. Exciton coupling in the "face-to-face" stacking results in an allowed state at higher energy than the monomer state and a forbidden state at lower energy (30,44). The y-oxo dimer emits both... 

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