The alternant hydrocarbon pairing theorem and all-valence electrons theory. An approximate LCOAO theory for the electronic absorption and MCD spectra of conjugated organic compounds, part 2

Abstract

An approximate linear combination of orthogonalized atomic orbitals (LCOAO) all-valence electrons theory is described, based on a previously suggested partitioning of the Fock operator. Kinetic energy and penetration terms are evaluated explicitly in a LoÈ wdin OAO basis, while two-electron repulsion terms are treated according to the conventional neglect of dierential overlap (NDO) approximation. One-electron and penetration integrals are parameterized explicitly to predict approximate alternant pairing symmetry for the p-systems of benzene and napthalene. Application of the resulting LCOAO theory to a variety of alternant and non-alternant hydrocarbons demonstrates signi®cant improvements in the prediction of MCD B-terms and transition moment directions, particularly for alternant (4N+2)-or 4N-perimeter p-systems for which traditional NDO procedures fail.

UV polarisation spectroscopy of 1,4-diethynylbenzene

“…Additional calculations were carried out with the Linear Combination of Orthogonalized Atomic Orbitals (LCOAO) method [44][45][46]. This semiempirical all-valence-electrons procedure was developed for the prediction of electronic transitions and Magnetic Circular Dichroism (MCD) B-terms [47] for conjugated organic compounds.…”

“…This semiempirical all-valence-electrons procedure was developed for the prediction of electronic transitions and Magnetic Circular Dichroism (MCD) B-terms [47] for conjugated organic compounds. It has been applied to several conjugated hydrocarbons containing triple-bonded linkages [45,48,49]. The LCOAO results are listed in S9.…”

Electronic States of Anthanthrene. Linear and Magnetic Circular Dichroism, Fluorescence Anisotropy, and Quantum Chemical Calculations

“…26). This is an all-valence electrons model developed with particular empbasis on a description of tbe alternant pairing properties of benzenoid PAHs and has beensbown to yield excellent results for a variety of systems (25,26). In particular, [he model leads to .satisfactory predictions of MCD B-terms and transition moment direct ions for planar PAHs with Cs or C211 symmetry, such as benz|a|anthracene (13).…”

“…The molecular geometry of anthanthrcne (C2ii symmetry) was taken as the one computed with the Gaussian98 software package (27) by using B3LYP density functional theory and the 6-31G* basis sel (23,28). The 64 singly excited 7T-7T* configurations generated by excitation from the 8 highest JT to the 8 lowest n* orbitals were included in the Configuration Interaction (CI) calculation (25). The results are listed in Table I and shown graphically in (0 where the sums run over the transitions / contributing to tbe spectra.…”

“…HIectronic iransitions predicted by ihe LCOAO meth(xl, wilh indication nfin-ptane triinsition nioniciil anj;lL\s <p and MCI) B-tcnns in units ol" 10"' Pe Debye'/cm"'(25). Trun.silii)ns Ibihiddcn by syniniclry are indicalcd by circles.…”