Exciton coupling between enones: Quassinoids revisited

Abstract

The electronic circular dichroism (ECD) spectra of two previously reported quassinoids containing a pair of enone chromophores are revisited to gain insight into the consistency and applicability of the exciton chirality method. Our study is based on time-dependent Density Functional Theory calculations, transition and orbital analysis, and numerical exciton coupling calculations. In quassin (1) the enone/enone exciton coupling is quasi-degenerate, yielding strong rotational strengths that account for the observed ECD spectrum in the enone π-π* region. In perforalactone C (2) the nondegenerate coupling produces weak rotational strengths, and the ECD spectrum is dominated by other mechanisms of optical activity. We remark the necessity of a careful application of the nondegenerate exciton coupling method in similar cases.

ECD exciton chirality method today: a modern tool for determining absolute configurations

“…Adapted from ref. 38 Copyright 2017, with permission from Wiley π-π* transition, which is polarized along the double bond direction and normally occurs at 195 nm. Nonetheless, this transition may be excitonically coupled to a second transition, for example, a benzoate π-π* transition.…”

Specific chiroptical sensing of cysteine via ultrasound-assisted formation of disulfide bonds in aqueous solution

“…As three prerequisites for the application of ECM were satisfied, the helicity of transition dipole moments between NBD-R groups resulted in an ECCD spectrum with two bisignate CEs ( Fig. 4 e-4g) [39] , [59] , [60] . According to the positive CE at longer wavelengths (498 nm), a clockwise screw of two transition dipole moments was deduced ( Fig.…”

Isolation, stereochemical study, and racemization of (±)‐pratenone A, the first naturally occurring 3‐(1‐naphthyl)‐2‐benzofuran‐1(3H)‐one polyketide from a marine‐derived actinobacterium

“…For the ( R ) configuration, the two transition dipoles define a positive chirality (that is, a clockwise rotation is necessary to move the dipole in the front onto that in the back, shown in Figure ), which is in accord with the positive couplet found for (+)‐ 1 . It must be stressed that a correct application of the exciton chirality method necessitates various prerequisites to be met, the most important of which is, in the current case, an accurate knowledge of the transition moment directions. These latter (depicted in Figure ) were easily obtained by means of quick TDDFT calculations on the relevant chromophores (see details in Section 2.6).…”