Experimental Evidence of the Molecular and Macroscopic Origins of Circular Dichroism in Chiral Metal-Halide Networks

Clockwise or counter-clockwise spin coating? In the current hot research topic of chiral metal-halide semiconductors, several investigations have been undertaken in order to reveal their natural optical activity and have reported dissymmetry factors (gabs) for thin films of many hybrid compounds, usually without considering the macroscopic anisotropies inherent to solid-state samples. Yet, CD in the solid state can be strongly modulated by the co-existence of linear dichroism (LD) and linear birefringence (LB). Theoretical studies recently revealed the importance of such macroscopic interferences in the CD response of solid-state samples, often referred as symmetric (sLDLB) and antisymmetric (aLDLB) effects. Based on the newly synthesized one-dimensional lead-halide networks of formula (S/R-HP1A)PbBr3 and (S/R-HP1A)PbI3, an experimental method to accurately discriminate between CD, sLDLB and aLDLB in chiral metal-halide networks is here presented. The main experimental conditions influencing sLDLB and aLDLB amplitude are also highlighted, such as the concentration of the precursor solution and the spin-coating rotation direction, finally providing a complete experimental guide for the forthcoming chiroptical investigations of such important family of chiral hybrid materials. A complete experimental circular dichroism (CD) study on new chiral metal-halide thin films allows to discriminate between molecular CD and all possible macroscopic effects resulting from sample thickness or local anisotropy. The results bring important information about the origins of chiroptical activity in metal-halide semiconductors and provide a guide for disclosing the pure molecular CD in a large range of hybrid materials. image