Chiral organic thin films: How far pulsed laser deposition can conserve chirality

We have investigated the pulsed laser deposition (PLD) technique to grow isotropic thin films based on bridged binaphthyls. We have focused on the conservation of the chiroptical properties during the deposition process. Chiral high purity liquid chromatography reveals that all the molecules are damaged at the same laser power threshold, but that below this threshold, neither bridged binaphthyl nor binaphthol undergo racemization. In situ circular dichroism spectra, as well as optical rotation (OR) measurements, confirm these findings. Isotropic 2 μm thick films with OR of 20°/mm at 546 nm were deposited. Furthermore, an estimation of the thermal load reveals that, due to its instantaneous nature, PLD does not induce thermal degradation. Only photochemical processes are involved in both racemization and degradation.

► Pulsed laser deposition can produce organic isotropic chiral thin films. ► Depending on the molecular structure, the chirality can be transferred to the films. ► No thermal racemization was observed during the process. ► Photoracemization occurs only for a given molecular structure. ► High optical rotation (20°/mm at 546 nm) was measured on a bridged binaphthyl film.