Insight into the Influence of the Chiral Molecular Symmetry on the Chiroptics of Fluorescent BINOL-Based Boron Chelates

Abstract

The prominent influence of the molecular symmetry, as defined by the symmetry point group, on the chiroptical behavior (electronic circular dichroism and, especially, circularly polarized luminescence) of simple fluorescent boron chelates (BODIPY and related BOPHY analogues) is studied and discussed. It is shown that increasing the dye symmetry by means of the D3 chiral symmetry group is a workable design option to enhance the level of differential emission of rightand left-circularly polarized light in BODIPY dyes and related emitters. And that the influence of the level of symmetry is stronger than the influence of the higher number of chiral moieties perturbing the acting achiral chromophore.

Ligand Shell Isomerization Induces Different Fluorescence Origins of Two Au28 Nanoclusters

“…The small structural relaxation of the Au 28 (CHT) 20 nanocluster leads to less energy dissipation (via a small relaxation energy of 0.18 eV). The present studies suggested that the symmetry of the nanoclusters is an important factor in the photoluminescence of ligand-protected gold nanoclusters, similar to the case of organic molecules. ,,− The higher quantum yield of Au 28 (CHT) 20 can be attributed to its highly symmetric structure, which leads to a small distortion in the geometric structure between the ground and excited states and hence less energy dissipation during the structural relaxation process. In addition, the small Franck–Condon factor of the S 1 → S 0 transition together with the allowed S 2 → S 0 transition in Au 28 (CHT) 20 results in mutual orthogonality between the S 2 and S 1 states, which reduces the rate of S 2 → S 1 internal conversion and hence provides a longer life span of the S 2 state .…”

Enhanced Chiral Exciton Coupling in Neat Molecular Films

“…Recently, Sánchez-Carnerero et al demonstrated that a conjugate of an achiral BODIPY with a chiral BINOL ( O -BODIPY) shows both CD and circularly polarized light emission in the visible range above wavelengths of 500 nm . Thanks to the simplicity of the synthesis, a new variety of O -BODIPY compounds has been developed that absorbs light from the ultraviolet to the near-infrared ranges of the optical spectrum. − …”