Triplet energy transfer from CuInS₂/ZnS nanorods to organic molecules for photon upconversion

Triplet sensitization of semiconductor nanocrystals is important in photocatalysis and photodynamic therapy. However, current photosensitizers often contain toxic or precious metals, making the development of environmentally benign nanocrystal-based systems challenging due to scarce suitable materials and insufficient understanding of excited-state transfer. Herein, we investigate triplet energy transfer from CuInS₂/ZnS nanorods to surface-anchored 9-anthracene carboxylic acid acceptors, with a rate constant of 1.02 × 10¹⁰ s^-1 and 90% efficiency. Besides, the transferred spin-triplet states undergo triplet-triplet annihilation in the interfaced annihilator molecules of diphenyl anthracene, enabling photon upconversion with a threshold of 23.26 W/cm² and an efficiency of 6.8%. These findings highlight CuInS₂/ZnS nanorods as nontoxic triplet sensitizers and provide a viable strategy for sustainable upconversion optoelectronic devices.