Non-transient thermo-/photochromism of iodobismuthate hybrids directed by solvated metal cations

Two iodobismuthate-based organic-inorganic hybrids, [M(DMSO)(8)][Bi2I9] (M = La (1), Bi (2)), have been successfully designed and synthesized by using solvated metal cations as structure-directing agents (SDAs). 1 displays transient high-temperature thermochromism, which is similar to that of the characteristic low-temperature thermochromic properties of bulk bismuth iodide and iodobismuthate hybrids. In contrast, 2 exhibits distinguishing non-transient thermochromic properties stimulated by the different temperature ranges of the thermal treatments. More importantly, a comparison of the optical inertness of 1 and 2 also reveals novel photochromic behavior. The completely different thermo-/photo-responsive properties of 1 and 2 are mainly ascribed to the different binding abilities of the central metal cations with DMSO molecules, which cause a distinct transformation of the inorganic moiety and consequent modulation of band gaps.