Lead(II)-Based Coordination Polymer Exhibiting Reversible Color Switching and Selective CO₂ Photoreduction Properties

Herein, we report a new photofunctional Pb-S-based coordination polymer (CP) with the formula [Pb(ATAT)(OAc)] (ATAT = 3-amino-5-mercapto-1,2,4-triazole, OAc = acetate, CP1). Apart from its photoactive one-dimensional (1D) (-Pb-S-) chain, CP1 is also composed of another 1D (-Pb-O-) chain that originates from the coordination with acetate. The coordinated acetate can be exchanged with water (H₂O) or dimethyl sulfoxide (DMSO), leading to the formation of a CP1-HO or CP1-DMSO structure that exhibits a distinct change in optical properties, including a white-to-yellow color change. The structural transformation of CP1 to CP1-HO and CP1-DMSO, and its subsequent recovery to the original CP1 structure could be controlled by the presence or absence of acetic acid vapor; the transformation was completely reversible. CP1 absorbed light with wavelengths shorter than 390 nm, with an estimated bandgap of 3.18 eV. Density functional theory calculations indicated that the valence band of CP1 is mainly formed by N and S orbitals originating from the ATAT unit, whereas the conduction band is composed of the Pb orbitals. Even without any modification, such as the incorporation of a molecular catalyst, CP1 reduced CO₂ into formate under UV light with >99% selectivity.