Helitwistacenes-Combining Lateral and Longitudinal Helicity Results in Solvent-Induced Inversion of Circularly Polarized Light.

Helicity is expressed differently in ortho- and para-fused acenes-helicenes and twistacenes, respectively. While the extent of helicity is constant in helicenes, it can be tuned in twistacenes, and the handedness of flexible twistacenes is often determined by more rigid helicenes. Here, we combine helicenes with rigid twistacenes consisting of a tunable degree of twisting, forming helitwistacenes.

The effect of axial and helical chirality on circularly polarized luminescence: lessons learned from tethered twistacenes.

The effect of axial and helical twisting on the circularly polarized luminescence of acenes was studied both experimentally and computationally, using four series of tethered twisted acenes. We find that the combination of axial and helical chirality yields the highest anisotropy factors, and that the ratio between the absorption and emission anisotropy factors is an intrinsic property for twistacenes.

Circularly polarized and total luminescence as probes of nucleation and growth in chiral nanocrystals.

Nucleation of crystals as well as their growth is difficult to study experimentally. We have recently demonstrated that chiral Eu -doped terbium phosphate nanocrystals are an interesting system for studying nanocrystal formation mechanisms and chiral symmetry breaking, occurring during their formation, directed by chiral ligands, such as tartaric acid. In this paper, we show how simultaneous, in situ monitoring of both total emission intensity and circularly polarized luminescence magnitude and sign versus time during nanocrystal formation provides considerable information on the mechanisms of nanocrystal nucleation and growth.

A Kinetic Isotope Effect in the Formation of Lanthanide Phosphate Nanocrystals.

Mechanisms of nucleation and growth of crystals are still attracting a great deal of interest, in particular with recent advances in experimental techniques aimed at studying such phenomena. Studies of kinetic isotope effects in various reactions have been useful for elucidating reaction mechanisms, and it is believed that the same may apply for crystal formation kinetics. In this work, we present a kinetic study of the formation of europium-doped terbium phosphate nanocrystals under acidic conditions, including a strong H/D isotope effect.

Time-resolved circularly polarized luminescence of Eu -based systems.

Chiral Eu -based systems are frequently studied via circularly polarized luminescence spectroscopy. The emission lifetimes of each circular polarization, however, are virtually always ignored, because in a homogeneous sample of emitters, there should be no difference between the two. However, we show that in less robust Eu complex structures, as in the chiral complex Eu (facam) , a difference in the lifetimes of the two circularly polarized emission components arises due to heterogeneity of the complexes.