Highly circularly polarized broad-band emission from chiral naphthalene diimide-based supramolecular aggregates†
We report off-white circularly polarized luminescence (CPL) from supramolecular aggregates formed by a chiral carboxylic acid-functionalized naphthalene diimide. The self-assembly behaviour and the stability of the aggregates in solution were assessed by variable-temperature UV-Vis and electronic circular dichroism experiments. The observed 200 nm-wide emission band is unusual for a single chromophore and is a consequence of the supramolecular ordering due to a combination of π-stacking and H-bonding interactions, leading to excimer formation. High emission anisotropy factors glum, around |1–2| × 10−2, were observed over the whole spectrum in chlorinated/hydrocarbon solvent mixtures, as well as in thin films. These values are one order of magnitude higher than those of most chiral self-assembled fluorophores and other common small organic emitters.