Single-Site Ru(II) in a BODIPY-Based Conjugated Porous Polymer-TiO₂ Heterostructure: A Case Study of Photothermal...

This work explores the photothermal Nitrogen Reduction Reaction (NRR) to ammonia over a hybrid catalyst composed of TiO₂ and a BODIPY-based conjugated porous polymer functionalized with a Ru(II) complex. The metal-organic conjugated porous polymer, denoted IEP-37 (IMDEA Energy Polymer number 37), was synthesized by incorporating a (dipyrrin)(bipyridine)ruthenium(II) complex into a BODIPY network and subsequently integrated with anatase TiO₂ nanoparticles to form a IEP-37@T-10 heterostructure. Extended X-ray absorption fine structure analysis indicates the presence of isolated Ru coordination sites, with no detectable Ru-Ru coordination. Under photothermal conditions, IEP-37@T-10 achieved approximately fivefold higher NH₃ production than pristine TiO₂, and a 3.5-fold enhancement compared with the Ru-free hybrid analogue, highlighting the essential role of Ru incorporation in the NRR activity of the system. The hybrid IEP-37@T-10 showed good photochemical and thermal stability and retained measurable activity over consecutive reaction cycles. The NH₃ yield obtained under simultaneous light and heat activation exceeded the contributions of the individual photocatalytic and thermocatalytic processes, suggesting a cooperative interaction between photochemical and thermally driven pathways. Time-resolved spectroscopic studies indicate that Ru incorporation modifies the interfacial charge transfer dynamics between the polymer and TiO₂, consistent with a direct Z-scheme-type charge transfer pathway compared with the Type-II behavior observed in the Ru-free hybrid. These findings highlight the influence of Ru incorporation on the charge transfer dynamics of the hybrid system and illustrate the potential of BODIPY-based polymer-semiconductor heterostructures for light-assisted nitrogen reduction.