Can Magnetic Dipole Transition Moment Be Engineered?

Abstract

The development of chiral compounds with enhanced chiroptical properties is an important challenge to improve device applications. To that end, an optimization of the electric and magnetic dipole transition moments of the molecule is necessary. Nevertheless, the relationship between chemical structure and such quantum mechanical properties is not always clear. That is the case of magnetic dipole transition moment (m) for which no general trends for its optimization have been suggested. In this work we propose a general rationalization for improving the magnitude of m in different families of chiral compounds. Performing a clustering analysis of hundreds of transitions, we have been able to identify a single group in which |m| value is maximized along the helix axis. More interestingly, we have found an accurate linear relationship (up to R2=0.994) between the maximum value of this parameter and the area of the inner cavity of the helix, thus resembling classical behavior of solenoids. This research provides a tool for the rationalized synthesis of compounds with improved chiroptical responses.

Chiral π-Conjugated Double Helical Aminyl Diradical with the Triplet Ground State

“…62−64 Notably, the enantiomer of neutral tetraamine (PP)-2-H 2 -C 2 exhibits moderately strong chirooptical properties, as determined by the absorption anisotropy factor, |g| = |Δε|/ε = 0.036 at λ = 376 nm (Figure 6). This factor is comparable to |g| = 0.039 and 0.035 reported for other double helices, carbon−sulfur, and bis-perylene diimide, 65,66 but smaller than |g| = 0.052 for expanded [23]helicene 67,68 and |g| = 0.20 for Zn(II)helicate. 62,69 The barrier for racemization of tetraamine (MM)-2-H 2 -C 2 (%ee 94.4) is measured at 210, 230, and 250 °C by using two solid samples at each temperature.…”

“…The ECD spectrum with the negative couplet at the longest wavelength is invariably associated with the ( M ) and ( MM ) enantiomers of helical and double helical π-systems, , with many exceptions for double helical systems. − Notably, the enantiomer of neutral tetraamine ( PP )- 2 -H 2 - C 2 exhibits moderately strong chirooptical properties, as determined by the absorption anisotropy factor, | g | = |Δε|/ε = 0.036 at λ = 376 nm (Figure ). This factor is comparable to | g | = 0.039 and 0.035 reported for other double helices, carbon–sulfur, and bis-perylene diimide, , but smaller than | g | = 0.052 for expanded [23]­helicene , and | g | = 0.20 for Zn­(II)-helicate. , …”

Chiral π-Conjugated Double Helical Aminyl Diradical with Triplet Ground State

“…[62][63][64] Notably, the enantiomer of neutral tetraamine (PP)-2-H2-C2 exhibits moderately strong chirooptical properties, as determined by the absorption anisotropy factor, |g| = |Δε|/ε = 0.036 at  = 376 nm (Figure 6). This factor is comparable to |g| = 0.039 and 0.035 reported for other double helices, carbon-sulfur and bis-perylene diimide 65,66 but smaller than |g| = 0.052 for expanded [23]helicene 67,68 and |g| = 0.20 for Zn(II)-helicate. S2.1, SI).…”

Can Deep Learning Search for Exceptional Chiroptical Properties? The Halogenated [6]Helicene Case

“…Being a component of the equation, very low |m 0j | values result in very poor chiroptical response. This value is maximized when the transition involves the extended helicene π-orbitals, 48 while localized π-orbitals usually give low |m 0j | values. On the other hand, the angle θ is also critical.…”