Electronic structure, polyenes

Hudson, B.S., Kohler, B.E., Schulten, K. (1982), Linear Polyene Electronic Structure and Potential Surfaces, in Excited States 6 Lim, E.C., Ed. Academic Press New York. 

Hudson BS and Kohler BE (1973) Polyene spectroscopy the lowest energy excited singlet state ofdiphenyloctatetraene and other linear polyenes. J Chem Phys 59 4984-5002 Hudson BS and Kohler BE (1974) Linear polyene electronic structure and spectroscopy. Ann Rev Phys Chem 25 437-460 Hudson BS and Kohler BE (1984) Electronic stmcture and spectra of finite linear polyenes. Synthetic Metals 9 241-253 Hudson BS, Ridyard JN and Diamond J (1976) Polyene spectroscopy. Photoelectron spectra of the diphenylpolyenes. J Am Chem Soc 98 1126-1129 Hudson BS, Kohler BE and Schulten K (1982) Linear polyene electronic structure and potential surfaces. In Lim EC (ed) Excited States, Vol 6, pp 1-95. Academic Press, New York Jones PF, Jones WJ and Davies B (1992) Direct observation of the 2 Ag electronic state of carotenoid molecules by consecutive two-photon absorption spectroscopy. Photochem Photohiol A Chem, 68 59-75... 

B. Hudson, B. Kohler, and K. Schulten, Linear polyene electronic structure and potential surfaces, in E.x-cited States (C. Lim, ed.). Academic, New York. 1982, Vol. 6, p. 1. 

Kohler, B. E., A simple model for linear polyene electronic structure, 7. Chem. Phys., 93,5838, 1990. 

The discussions of linear polyene electronic structure that follow are made clearer by reference to a simple quantum mechanical model. In this section we briefly sketch the model that we use. A fuller description will be published elsewhere [3]. 

Since Schulten and Karplus showed that the experimentally observed ordering of polyene excited states reflected the importance of electron correlation in these molecules [2], the idea that explicit consideration of electron-electron coulomb interaction is essential for a correct description of polyene electronic structure has been reinforced by a number of theoretical studies [4-8]. Unfortunately, as theory more closely agrees with experiment, it also becomes more complex and computationally intensive. This is the reason that we have... 

When the 7r-systerns of two or more double bonds overlap, as in conjugated dienes and polyenes, the 7r-clccIrons will be delocalized. This has chemical consequences, which implies that the range of possible chemical reactions is vastly extended over that of the alkenes. Examples are various pericyclic reactions or charge transport in doped polyacetylenes. A detailed understanding of the electronic structure of polyenes is therefore of utmost importance for development within this field. We will first discuss the structure of dienes and polyenes based on theoretical studies. Thereafter the results from experimental studies are presented and discussed. 

Electronic structure of diene and polyene radical cations... 

For many years, investigations on the electronic structure of organic radical cations in general, and of polyenes in particular, were dominated by PE spectroscopy which represented by far the most copious source of data on this subject. Consequently, attention was focussed mainly on those excited states of radical ions which can be formed by direct photoionization. However, promotion of electrons into virtual MOs of radical cations is also possible, but as the corresponding excited states cannot be attained by a one-photon process from the neutral molecule they do not manifest themselves in PE spectra. On the other hand, they can be reached by electronic excitation of the radical cations, provided that the corresponding transitions are allowed by electric-dipole selection rules. As will be shown in Section III.C, the description of such states requires an extension of the simple models used in Section n, but before going into this, we would like to discuss them in a qualitative way and give a brief account of experimental techniques used to study them. 

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