Interfacial Self-Assembly of Organized Ultrathin Films of Tripodal Metal-Terpyridyl Coordination Polymers as Luminophores and Heterogeneous Catalysts for Photocatalytic CO₂ Reduction

Abstract

Metal-directed interfacial self-assembly of well-defined coordination polymer (CP) ultrathin films can control the metal complex arrangement and distribution at the molecular level, providing a convenient route for the design and fabrication of novel opto-electrical devices and heterogeneous catalysts. Here, we report the assembly of two series of CP multilayers with the transition-metal ions of Fe2+, Co2+, Zn2+ and Tb3+ as connectors and tripodal terpyridyl ligands of 4,4′,4″-(1,3,5-triazine-2,4,6-triyl)­tris­(1-(4-([2,2′:6′,2″-terpyridin]-4′-yl)­benzyl)­pyridin-1-ium) (TerPyTa) and 4,4′,4″-(benzene-1,3,5-triyl)­tris­(1-(4-([2,2′:6′,2″-terpyridin]-4′-yl)­benzyl)­pyridin-1-ium) (TerPyBen) as linkers at the air–water interface. The as-prepared Langmuir–Blodgett (LB) films display strong luminescence, with the emission wavelength and relative intensity dependent on both the metal ions and linkers; among them, the Zn-TerPyTa and Zn-TerPyBen CPs give off the strongest luminescent emission centered at about 370 nm with an emission lifetime of approximately 0.2–0.3 ns. The Tb-TerPyTa CPs can give off emission at approximately 490, 546, 586, and 622 nm, attributed to the 5D4 to 7F3–6 electron transitions of typical Tb3+ ions. Finally, these CP LB films can act as efficient heterogeneous photocatalysts for the CO2 reduction to selectively produce CO. The catalytic efficiency can be optimized by adjusting the experimental conditions (light sensitizer, electron donor, and water content) and CP composition (metal ion and ligand) with an excellent yield of up to 248.1 mmol g–1. In particular, it is revealed that, under the same conditions, the catalytic efficiency of the Fe-TerPyTa CP LB film is nearly 2 to 3 orders of magnitude higher than that of the other metalated complexes investigated in the homogeneous system. UV–vis spectroscopy and cyclic voltammetry studies demonstrated that the dual active sites of Fe-terpyridine and TerPyTa units contribute to the enhanced catalytic activity. This work provides an effective method to introduce the earth-abundant metal complexes into CP films to construct efficient noble-metal-free photocatalysts for the CO2 reduction.

Unveiling dual catalysis enhancement of a pyridinium-containing Zn(ii) coordination polymer in aerobic photooxidation of organic substrates and selective photoreduction of CO2

“…The electron migration from the photosensitizer to Py3tpyZn may also be realized through other 4CzIPN-related species such as 4CzIPN* or 4CzIPN˙ − *. 20,41,54,63 As a result, the terpyridine unit and pyridinium unit in Py3tpyZn are reduced into the corresponding radical anion and radical species, respectively. This is consistent with the observation in Fig.…”

“…36–40 Particularly, the redox-active feature of terpyridine-based ligands allows corresponding CPs to promote efficient photoreduction of CO 2 . 21,41–44 As a heterogeneous form of molecular metal–terpyridine complex, metal–terpyridine CPs not only show good recyclability but also have potential tunability via ligands and metals like homogeneous molecular catalysts. However, metal–terpyridine CPs have limitations for use in photoreduction reactions.…”

Photoinduced morphological transformation of a self-assembled iron(ii) coordination polymer: high-performance, non-precious metal, and self-enhancing photocatalytic CO2 reduction

“…[3][4][5][6][7][8][9][10][11] Among numerous homogeneous and heterogeneous catalysts, transition metal coordination polymers are emerging as superior catalysts for CO 2 photoreduction owing to versatile metal centers, tunable organic ligands, and rich structural morphologies. [12][13][14][15] Coordination polymers are commonly heterogeneous and recyclable through facile separation after catalysis, making them potentially attractive in industrial applications. Initially, precious metal coordination polymers containing Re, Ir, and Ru elements were used for CO 2 photoreduction.…”

Manipulating the Coordination Structure of Molecular Cobalt Sites in Periodic Mesoporous Organosilica for CO2 Photoreduction

“…In CO 2 photoreduction studies with a traditional Ru­(bpy) 3 Cl 2 photosensitizer (denoted as [Ru-PS]) and an organic TADF dye (4CzIPN), MN x -PMO catalysts displayed distinct CO evolution activity with CoN 5 -PMO exhibiting superior performance than the other three materials. 4CzIPN was selected as the sensitizer because it has been shown to be a cost-effective option for photoredox catalysis, and its use in CO 2 reduction photosystems was recently demonstrated for molecular iron-terpyridine and manganese-bipyridine catalysts. − ,− The coordination environment around Co in CoN 5 -PMO was confirmed by X-ray absorption spectroscopy (XAS), and the origin of the activity at the CoN 5 -active site was supported by mechanistic studies on a molecular CoN 5 analogue.…”