Soft-Matter Confinement Modulates Excited-State Dynamics of Ru Photocatalysts for Hydrogen Evolution in Aqueous Media

The development of photochemical molecular devices (PMDs) is essential for the mechanistic understanding of solar-to-fuel conversion, yet translation from homogeneous solution to heterogeneous systems remains largely unexplored, as molecular confinement may lead to unpredictable reactivity and dynamics. Here, we report Ru-based photosensitizer─bridging ligand─Rh/Pt catalyst assemblies, as well-characterized model systems, immobilized within electrospun polyacrylonitrile (PAN) nanofibers as a soft-matter matrix for light-driven hydrogen evolution in fully aqueous media. Structural and spectroscopic analysis (SEM, XPS, EDX, ATR-IR, FT-Raman, O-PTIR, NMR, UV–vis and diffuse reflectance) confirmed homogeneous distribution and chemical integrity of the molecular components after they have been embedded into the nanofibrous soft-matter matrix. Steady-state emission revealed that the polymer matrix alters the local environment around the complex, destabilizing the π* orbital energy of the tpphz bridge. Emission and femtosecond transient absorption (fsTA) spectroscopy further demonstrated that the surface and buried complexes give different contributions to excited-state dynamics, which is significantly different from what was observed for solution. Light-driven hydrogen evolution experiments confirmed the activity of all fibers containing the catalytic Rh or Pt centers. The observable photocatalytic activity is determined by the nature of the catalytic center and is only insignificantly altered upon immobilization into the PAN matrix. The nanofibers enable stable photocatalysis with environmentally benign sacrificial donors, suppress leaching, and preserve the molecular integrity under catalytic turnover. These findings highlight how a soft-matter environment modulates the photophysical pathways of molecular photocatalysts and provides mechanistic insight into designing fiber-supported systems for sustainable hydrogen evolution in aqueous media.