Molecular orbitals chromophore

Indigo is the most important vat dye, dating back to ancient times and produced on an industrial scale since 1880. To replace the indigo dyes, the indanthrone (21) class of dyes was developed. Indanthrone has superior characteristics as a vat dye and became a key material for further development of anthraquinoid vat dyes. There exist a variety of anthraquinone vat dyes differing in the chromophoric system. The color-structure relationship of vat dyes have been rationalized by the Pariser-Parr-Pople molecular orbital (PPP MO) method. Some examples of commercialized anthraquinoid vat dyes are shown in Scheme 6.14... 

In our first ONIOM study, we showed the advantages of combining two molecular orbital (MO) methods in calculations of the chromophore itself. Compared to a full CASSCF treatment of a scaled chromophore (PSBN in Figure 2-3), a two-layer ONIOM (CASSCF CIS) calculation where only parts of the conjugated system (PSBN8 in Figure 2-3) is included in the model system, reproduces the... 

Figure 2.13 n and k molecular orbitals associated with the >C=C< chromophore. Both the n- and Ji -orbitals lie in the plane of the paper... 

The reducing character of the ligand is linearly related to the relative position of the first spin-allowed transition and the first electron transfer transition. Jorgensen 233) calculated the optical electronegativity of ethyl-dsep as 2.6 which is close to that of ethyl-dtp, 2.7. Jorgensen 233) has also discussed electron delocalization in M(X2P)3 (X = S, Se) chromophores in terms of a molecular orbital model. 

In spite of the absence of a typical chromophore, 1,2-dithiin is a bright reddish-orange color. Absorption maxima were found at 451 (2.75 eV), 279 (4.36 eV), and 248 nm (5.00 eV), and the colored band was assigned to a A excitation <1991JST(230)287>. The main reason for the colored absorption of 1,2-dithiin is the low HOMO-LUMO gap of the KS orbitals which amounts to only 3.6 eV (HOMO = highest occupied molecular orbital LUMO = lowest unoccupied molecular orbital KS = Kohn-Sham) <2000JMM177>. By comparison, saturated 1,2-dithiane is colorless (290 nm). 

The application of the angular overlap method to MXg chromophores of trigonal bipyramidal and square p3u-amidal stereochemistry leads to the patterns of Fig. 2 for the energies of the antibonding "d molecular orbitals (dc). The crystal field model leads to a similar pattern. 

The secondary structure of poly(iV-alkynylamides) is influenced by the position of the chiral center and amide group.The position of the chiral center mainly affects the helical pitch, which becomes short when the chiral center is positioned away from the main chain. The stability of the helical structure is also influenced by the position of the amide group. Based on molecular orbital study, it is concluded that poly(iV-propargylamides) with right-handed helical structure display a plus Cotton effect around 390 nm. This is also confirmed by the exciton chirality method using porphyrin as a chromophore. ... 

One important chromophore is a carbon-carbon double bond. In terms of the language of molecular orbital theory, the electronic transition that occurs when energy is absorbed is the excitation of an electron from... 

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