Supramolecular Control of Helicene CPL Emitters in Molecular Solids and Bright Nanoparticles.

ABSTRACT

Circularly polarized luminescence (CPL) from chrial molecules is attracting much attention due to its potential in optical materials. However, formulation of CPL emitters as molecular solids typically deteriorates photophysical properties in the aggregated state leading to quenching and unpredictable changes in CPL behavior impeding materials development. To circumvent these shortcomings, a supramolecular approach can be used to isolate cationic dyes in a lattice of cyanostar-anion complexes that suppress aggregation-caused quenching and which we hypothesize can preserve chiroptical properties. Herein, we verify for the first time that supramolecular assembly of small-molecule, ionic isolation lattices (SMILES), allows translation of molecular ECD and CPL properties to solids. A series of cationic helicenes that display increasing chiroptical response, is investigated. Crystal structures of three different packing motifs all show spatial isolation of dyes by the anion complexes. We observe the photophysical and chiroptical properties of all helicenes are seamlessly translated to water soluble nanoparticles by the SMILES method. Also, a DMQA helicene is used as FRET acceptor in SMILES nanoparticles of intensely absorbing rhodamine antennae to generate an 18-fold boost in CPL brightness. These features offer promise for reliably accessing bright materials with programmable CPL properties.