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.