Metal Nanoparticle Enhanced Molecular Triplet Generation for Singlet Oxygen Production and Antibacterial Application

Developing sensitizers for highly efficient molecular spin-triplet excited state generation is vital for many applications. Herein, we show Au and Pt nanoparticles as sensitizers for triplet generation in adjacent 9-anthracene carboxylic acid (ACA) molecules. Ultrafast spectroscopy reveals hole transfer from ACA to Au and Pt, with different time constants depending on the electronic structure of metal, followed by spin-flip in metal and charge recombination to produce triplet state (³ACA*). ³ACA* can transfer its energy to molecular oxygen to produce singlet oxygen (¹O₂), with quantum yields of 67.8% and 42.3% for Au-ACA and Pt-ACA, ∼3 and 2 times higher than that of free ACA, respectively. The nanoparticle-ACA nanohybrids show high antibacterial activity, attributed to the synergistic effect of nanoparticle enhanced ¹O₂ generation and photothermal effect from plasmonic hot carriers. This bifunctionality of metal nanoparticle-molecule nanohybrids is promising for many applications including photodynamic therapy and photocatalysis.