Universality of Metal Nanoparticles for Enhancing Molecular Triplet Generation: Metal-Dependent Effects and Extension of Triplet Generation from Interface to Solution

Molecular triplet states are essential for applications in photodynamic therapy, photocatalysis, and energy conversion. However, inefficient intersystem crossing limits their generation. Metal nanoparticles, with their tunable optical responses and rich surface electronic structures, are particularly attractive candidates for enhancing triplet generation. In this work, 1-pyrenecarboxylic acid (PCA) is used as a model molecule to construct Au-PCA, Ag-PCA, Pt-PCA, and Pd-PCA hybrids, enabling the investigation of the universality and metal-dependent effects of nanoparticle-enhanced triplet generation. Transient absorption spectroscopic results show a common kinetic sequence, 1PCA* → PCA– → 3PCA*, for the four metals, which involves interfacial hole transfer, a possible spin flipping, and charge recombination processes. Among the metals, Pt and Pd facilitate charge transfer through high densities of states near the Fermi level, whereas plasmonic Au and Ag further enhance triplet generation via possible plasmonic effects. As a result, the 1O2 quantum yields increase from 13.1% for PCA alone to 42.8%, 36.2%, 27.8%, and 23.8% for Au-PCA, Ag-PCA, Pt-PCA, and Pd-PCA, respectively. Au-PCA and Ag-PCA achieve near-complete inactivation of both Escherichia coli and Staphylococcus aureus. Furthermore, Au-PCA can sensitize RhB to form 3RhB* through solution-phase triplet energy transfer. This work highlights the universality of metal nanoparticles for enhancing triplet generation and reveals key metal-dependent effects that govern their generation and thus performance.