Pure chiral organic thin films with high isotropic optical activity synthesized by UV pulsed laser deposition

Abstract

We show that the pulsed laser deposition (PLD) technique allows us to elaborate pure molecular solid state thin films based on binaphthyl molecules featuring high isotropic optical rotation (HIOR). The transfer of chirality from the ablated target to the substrate was probed by polarimetry and circular dichroism (CD) measurements. A rotary power of 12° mm at 546 nm has been obtained. CD spectroscopy confirms both the chiral and the isotropical nature of the deposited thin films and put into evidence the disorder between the naphthyl chromophores inside the molecular material. Finally, we highlight three regimes for the deposition mechanism depending on the laser fluence: desorption without racemisation, desorption with racemisation, and ablation with degradation. These results demonstrate that, by properly adjusting the growth conditions, isotropic purely organic chiral films can be grown by PLD, thereby opening the prospect for the synthesis of high value organic materials for applications such as waveguiding.