Chemistry at the Solid–Gas Interface: Direct Crystalline Thin-Film to Thin-Film Chemical Transformation

Single-crystal to single-crystal transformation is an elegant example of altering a crystalline solid-state of matter to a solid-state with a different chemical identity. Herein, we present an alluring example of thin-film to thin-film transformation of metal–organic to metal–halide by exploring chemistry at the solid–gas interface. Exposure of crystalline AgTCNQ (TCNQ = 7,7,8,8-tetracyanoquinodimethane) thin-film to iodine (I₂) vapor and subsequent washing with chloroform (CHCl₃) generated crystalline AgI (silver iodide) thin-film. The chemical transformation AgTCNQ → AgI was so rapid that it took place within 2 min at ambient conditions. Reversible structural phase transition in the thin-film of AgI (β-phase ↔ α-phase) was further captured in variable temperature X-ray diffraction patterns, which appears promising for superionic conductivity and pyroelectricity applications.