Birefringent Color Filter by Layered Metal-Organic Chalcogenides: In-Plane Anisotropy and Odd/Even Effect

Anisotropic 2D materials are gaining interest recently as building blocks for angular-dependent optical/electrical devices. However, the fundamental understanding of their structure-property-relationship is limited, which hinders further modulation of their unique characteristics via structure tailoring. Here the in-plane structural anisotropy and the tunable optical/electrical properties of a series of radiation-sensitive (X-ray, e-beam) metal-organic chalcogenide (MOC) single crystals are comprehensively revealed with ligands of variable length/parity. Their monoclinic crystallography is determined at atomic resolution by a simple method that couples X-ray/electron diffraction with first-principles calculations. The in-plane inorganic backbone of the MOCs exhibits a strong lattice anisotropy with odd/even alternations, which originates from that of the out-of-plane organic motifs via organic/inorganic accommodation. Such structural anisotropy is implied mechanically by the preferred orientation of crystal cleavage. It triggers a maximum ≈8 × distinction of in-plane electrical conductivity of the semiconducting MOCs, plus a distinct birefringence (maximum Δn ≈ 0.03) with a dispersive orientation of dielectric axes, which rotate up to 25.7° from UV to visible-light regime, inspiring an emerging pathway for color filtering via single crystal rotation. Such in-plane optical characteristics also exhibit odd/even alternation and can be flexibly tuned by the designable out-of-plane ligands.