Tuned Range-Separated Time-Dependent Density Functional Theory Applied to Optical Rotation

For range-separated hybrid density functionals, the consequences of using system-specific range-separation parameters (γ) in calculations of optical rotations (ORs) are investigated. Computed ORs at three wavelengths are reported for methyloxirane, norbornenone, β-pinene, [6]helicene, [7]helicene, and two derivatives of [6]helicene. The γ parameters are adjusted such that Kohn–Sham density functional calculations satisfy the condition −ε^HOMO(<i>N</i>) = IP. For β-pinene, the behavior of the energy as a function of fractional total charge is also tested. For the test set of molecules, comparisons of ORs with available coupled-cluster and experimental data indicate that the γ “tuning” leads to improved results for β-pinene and the helicenes and does not do too much harm in other cases

Does a Molecule-Specific Density Functional Give an Accurate Electron Density? The Challenging Case of the CuCl Electric Field Gradient

In the framework of determining system-specific long-range corrected density functionals, the question is addressed whether such functionals, tuned to satisfy the condition −ε^HOMO = IP or other energetic criteria, provide accurate electron densities. A nonempirical physically motivated two-dimensional tuning of range-separated hybrid functionals is proposed and applied to the particularly challenging case of a molecular property that depends directly on the ground-state density: the copper electric field gradient (EFG) in CuCl. From a continuous range of functional parametrizations that closely satisfy −ε^HOMO = IP and the correct asymptotic behavior of the potential, the one that best fulfills the straight-line behavior of <i>E</i>(<i>N</i>), the energy as a function of a fractional electron number <i>N</i>, was found to provide the most accurate electron density as evidenced by calculated EFGs. The functional also performs well for related Cu systems

Ruthenium-Vinylhelicenes: Remote Metal-Based Enhancement and Redox Switching of the Chiroptical Properties of a Helicene Core

Introducing metal-vinyl ruthenium moieties onto [6]­helicene results in a significant enhancement of the chiroptical properties due to strong metal–ligand electronic interactions. The electro-active Ru centers allow the achievement of the first purely helicene-based redox-triggered chiroptical switches. A combination of electrochemical, spectroscopic, and theoretical techniques reveals that the helicene moiety is a noninnocent ligand bearing a significant spin density

Ruthenium-Vinylhelicenes: Remote Metal-Based Enhancement and Redox Switching of the Chiroptical Properties of a Helicene Core

Introducing metal-vinyl ruthenium moieties onto [6]­helicene results in a significant enhancement of the chiroptical properties due to strong metal–ligand electronic interactions. The electro-active Ru centers allow the achievement of the first purely helicene-based redox-triggered chiroptical switches. A combination of electrochemical, spectroscopic, and theoretical techniques reveals that the helicene moiety is a noninnocent ligand bearing a significant spin density

Giant Faraday Rotation in Mesogenic Organic Molecules

Faraday rotation, the rotation of the polarization of light due to a magnetic field in the direction of propagation of the light, is used in applications ranging from quantum memory to the detection of biomagnetic fields. For these applications large Faraday rotation is necessary, but absorption of light is detrimental. In search of these properties, we have characterized the Verdet constant of a so far unexplored class of mesogenic organic molecules. We report their spectra and provide an interpretation. A Verdet constant of almost 2.5 × 10⁵ deg T^–1 m^–1 is found around 520 nm. This Verdet constant is 3 orders of magnitude larger than the largest known for organic molecules in a region without spectral features. We attribute this enormous Faraday rotation to resonant enhancement by a triplet excitation that does not appear in the linear absorption spectrum and to near-resonant enhancement by low-energy singlet excitations. Furthermore we are able to switch the Faraday rotation by changing the liquid crystal phase of the compound. These results demonstrate a new class of Faraday rotating materials with great potential to replace current materials and improve existing applications. The inherent flexibility in the synthesis of this class of molecules opens a new field of research in Faraday rotation