Nanomorphology Control of Metallo-Supramolecular Polymers toward Photocatalytic CO 2 Reduction

The self-assembly of small molecules with a suitable metal ion is a critical bottom-up approach for preparing solution-processable metallo-supramolecular polymers and to realize their potential as a photocatalyst. Herein, we report the design, synthesis, self-assembly, and gelation behavior of a low-molecular-weight gelator (LMWG) based on a pyrene core connected to four terpyridine units (TPY-PY) through amide linkages. TPY-PY forms an organogel (OG) in the DMSO/H2O mixed solvent with a nanofibrillar morphology. In contrast, the introduction of RuII with the LMWG resulted in a Ru-TPY-PY coordination polymer gel (CPG) with a cross-linked fibrillar nanostructure with a length of several micrometers. The Ru-TPY-PY CPG exhibited highly efficient photoreduction of CO2 to CO (yield: 10.79 mmol g–1, rate: 899.17 μmol g–1 h–1) with 90% selectivity, under visible light irradiation, and in the presence of triethylamine (TEA) as a sacrificial electron donor. Moreover, metallo-supramolecular polymers with diverse nanomorphologies, formed at different RuII to TPY-PY ratios, showed different efficiencies in the photo reduction of CO2 to CO. Among these nanostructures, 1D nanofibers exhibited enhanced photocatalytic activity compared to the nanospheres for CO2 reduction, attributed to the abundance of catalytically active sites on their surface with facile CO2 diffusion capabilities. Furthermore, femtosecond transient absorption spectroscopy, in situ DRIFTS analysis, and DFT calculation help to understand the feasibility of the electron transfer pathway, and reaction mechanism in the overall process. The “soft” processable hybrid metal–organic supramolecular polymers that integrate both the catalytic site and the light-absorbing units are a class of catalysts showing efficient CO2 photoreduction to CO.