A homologous series of 4,7-bis(aryl) substituted benzothiadiazole (BTD) compounds, containing the helicenic derivatives bis([4]helicene), bis([5]helicene) and bis([6]helicene), have been prepared upon a double Suzuki coupling between 3,6-bis(pinacolyl-borane)-BTD and the corresponding bromo-aryl precursors. The single crystal X-ray structure of the bis([4]helicene) compound shows the existence of both helicities (M) and (P) on the same molecule. All the compounds of the series are highly emissive in solution, with quantum yields of the emission ranging from 50 to 91 %.
View Article and Find Full Text PDFIn this work, we present two compact basis sets optimized for the calculation of specific rotation: augD-3-21G and augT3-3-21G. They are obtained by combining the standard 3-21G basis set with the diffuse functions of aug-cc-pVDZ and aug-cc-pVTZ, respectively, followed by a reoptimization of the exponents of the diffuse functions. The exponent optimization is based on minimization of the root-mean-square relative error (RMSE) of the specific rotation computed at 589.
View Article and Find Full Text PDFIn this work, we describe a simple approach to select the most important molecular orbitals (MOs) to compute the optical rotation tensor through linear response (LR) Kohn-Sham density functional theory (KS-DFT). Taking advantage of the iterative nature of the algorithms commonly used to solve the LR equations, we select the MOs with contributions to the guess perturbed density that are larger than a certain threshold and solve the LR equations with the selected MOs only. We propose two criteria for the selection, and two definitions of the selection threshold.
View Article and Find Full Text PDFIn this work, we present an analysis of a series of helicene molecules to determine the driving forces for their large specific rotation, [α], and probe the effects of functionalization. The analysis is done in the configuration space of the molecular orbitals (MOs), and it allows us to decompose [α] into the component transition electric and magnetic dipoles from single MO excitations. We find that [α] for helicene molecules may be described by three sets of transitions based on the orientation of the magnetic dipole with respect to the helical axis: parallel, orthogonal, or tilted.
View Article and Find Full Text PDFA comparative theoretical and experimental study of dispersive optical activity is presented for a set of small, rigid organic molecules in gas and solution phases. Target species were chosen to facilitate wavelength-resolved measurements of specific rotation in rarefied vapors and in organic solvents having different polarities, while avoiding complications due to conformational flexibility. Calculations were performed with two density functionals (B3LYP and CAM-B3LYP) and with the coupled-cluster singles and doubles (CCSD) ansatz, and solvent effects were included through use of the polarizable continuum model (PCM).
View Article and Find Full Text PDFIntroduction of heterocycles into the helical skeleton of helicenes allows modulation of their redox, chiroptical, and photophysical properties. This paper describes the straightforward preparation and structural characterization by single-crystal X-ray diffraction of thiadiazole-[7]helicene, which was resolved into M and P enantiomers by chiral HPLC, together with its S-shaped double [4]helicene isomer, as well as the smaller congeners thiadiazole-[5]helicene and benzothiadiazole-anthracene. A copper(II) complex with two thiadiazole-[5]helicene ligands was structurally characterized, and it shows the presence of both M and P isomers coordinated to the metal center.
View Article and Find Full Text PDF