Pariser-Pople-Parr molecular orbital method

The molecular orbital (MO) approach developed more slowly but was ultimately much more successful than the other approaches. Dewar (1950) was able to predict absorption maxima for various types of cyanine dyes in excellent agreement with experiment. A major advance was made in 1953 when a self-consistent molecular orbital method specifically taking into account antisymmetrisation and electron repulsion effects was developed by Pariser, Parr and Pople. The PPP-MO method established itself over the next two decades as the most useful and versatile technique for colour prediction, especially when the microelectronics revolution provided facilities for overcoming the complexity of the necessary calculations. 

Electronic Spectra and Electronic Structure of Complex Unsaturated Molecules. I. See also, R. Pariser and R. Parr, J. Chem. Phys., 21, 767 (1953). A Semi-Empirical Theory of the Electronic Spectra and Electronic Structure of Complex Unsaturated Molecules. II. J. A. Pople, Trans. Faraday Soc., 49, 1375 (1953). Electron Interactions in Unsaturated Hydrocarbons. J. A. Pople, J. Phys. Chem., 61, 6 (1957). Application of Self-Consistent Molecular Orbital Methods to ti Electrons. 

More explicit molecular orbital methods including the electronic repulsion terms are called advanced molecular orbital methods. In such methods, F matrix elements of the Fock equation are calculated by Eqs. (6.6) and (6.7), and the iterative procedure, or self-consistent field (SCF) procedure must be used. The most convenient advanced molecular orbital method for the polycyclic aromatic compounds is the semiempirical method suggested by Pariser, Parr, and Pople (the PPP method). In this PPP method, the required integral values are empirically determined using the following approximations. 

In view of the inadequacy of the HMO method, attention turned in time to rather more elaborate MO approaches that remained reliant on semi-empiricism. A particular molecular orbital approach that was extensively applied to the calculation of the colour properties of dye molecules in the later decades of the twentieth century is the Pariser-Pople-Parr (PPP) method. Although the use of the PPP-MO method... 

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... 

When parameters of the Pariser-Parr-Pople configuration interaction molecular orbital (PPP-CI MO) method were modified so as to reproduce the Aol)s values for l,3-di(5-aryl-l,3,4-oxadiazol-2-yl)benzenes 16 and 17, the calculated HOMO and LUMO energy levels corresponded with the experimental ionization potential and electron affinity values. The relationships between the electrical properties and molecular structures for the dyes were investigated. The absorption maximum wavelengths for amorphous films were found to be nearly equal to those for solution samples <1997PCA2350>. 

M. Hida, unpublished results. b HMO, Hiickel molecular orbital theory. PPP, Pariser-Parr-Pople method. 

Among the earliest examples of the application of molecular orbital calculations to lignin chemistry is, as might be expected, the formation and reactivity of phenoxy radicals [32]. This work described the use of Pariser-Parr-Pople molecular orbital calculations, comparing various methods to determine the rr-electron spin densities for a number of model compounds. The different techniques gave similar results, with the bulk of the unpaired spin density at the phenolic oxygen, followed by the ortho and para carbons. In a cinnamaldehyde model, the P-position also exhibited considerable unpaired spin density. 

The Pariser-Parr-Pople method, self-consistent molecular orbital calculations, and the Huckel approach have been applied to the theoretical calculation of transition energies and intensities in the ultraviolet spectra of pyrido[2,3-ft]pyrazine and other azanaphthalenes. Good agreement with experimental data was obtained. The infrared spectra of the parent heterocycle" and its 8-hydroxy derivative have been discussed the 0X0 form is preferred to the hydroxy form both in chloroform solution and in the solid state. As with other a-hydroxyazines, the oxo form is also favored in the 2-, 3-, and 6-hydroxy compounds. Ultraviolet spectra have been measured for the parent heterocycle and various substituted compounds. The spectrum of the parent is substantially similar to other azanaphthalenes. In ethanol the principal bands are at ca. 260,300, and 350 nm. Both the infrared and ultraviolet spectra of about 60 derivatives of the ring system have been assembled. ... 

---