Structural determinations by circular dichroism spectra analysis using coupled oscillator methods: An update of the applications of the DeVoe polarizability model

Abstract

The exciton (coupled oscillator) model for optical activity is a very useful and powerful method which allows to analyze a circular dichroism (CD) spectrum in a nonempirical way, arriving at a safe assignment of the absolute configuration of organic and inorganic compounds. Usually in this model only the exciton coupling of two electrically allowed transitions (oscillators) is taken into account. This approach has the important advantage of an easy application but, sometimes, it may lead to wrong results. Thus, in this review article a more general treatment, which allows considering the simultaneous coupling of several oscillators, i.e., the DeVoe model, is presented and critically analyzed, discussing in detail the latest applications reported in the literature. In the authors opinion, since the DeVoe model joins generality and reliability requiring an almost negligible computational effort, it represents the method of choice for stereochemical assignments, even by nonspecialists.

EXAT: EXcitonic analysis tool

“…The application of the ECM to dimeric systems results in a simple chirality rule, which relates the sign of the CD Cotton effect to the sense of twist between the transition dipole moments of the two chromophores . However, in more complex cases, where many transitions are coupled, the interpretation of CD signatures is less straightforward . In these situations, applying the ECM requires a detailed analysis of the properties of the individual subunits, namely the excitation energies and the transition dipoles, and the excited‐state interaction between them, namely the exciton coupling.…”

On the Chiroptical Behavior of Conjugated Multichromophoric Compounds of a New Pseudoaromatic Class: Bicolchicides and Biisocolchicides

“…Equation (1), which was derived from a coupled oscillator approach [6], expresses the CD due to a series of transitions 1,2,3…i localized in the chromophores of the molecule and coupled through their dipole-dipole interactions. In this frame, transitions related to strongly conjugated electrons, such as those involved in the λ>300 nm spectral range, cannot be considered.…”

“…Equation (3) holds for two identical chromophores with one electrically-allowed transition, in the frame of a treatment first order in the dipole-dipole G 12 term [6]. …”

“…Models of such systems, built from either classical electrodynamics [3], [4] or quantum mechanics [5], can also allow a quantitative interpretation of the spectroscopic and structural terms that give rise to the exciton couplet [6] –[8]. However, except in the near-to-ideal cases, success is often limited to a few bands only.…”

Assignment of the absolute configuration of (+)-5,5′,6,6′-tetrahydro-7,7′-spiro[7H-cyclopenta[b]pyridine], a new inherently chiral spiropyridine, by a nonempirical analysis of its circular dichroism spectrum

“…Clearly in this case, we cannot use the simple 'exciton chirality rules' due to Harada and Nakanishi,[19][20][21][22] because in the case of (+)-1, we have two dipoles for each chromophore meaning that we have to treat the simultaneous interactions of four dipoles, whilst the above rules can be applied only in the case of two interacting dipoles. As a consequence, we have to use a more general exciton treatment; from this point of view the DeVoe model [23][24][25] can be considered the most useful one.…”