Nanoencapsulated Phase-Change Materials: Versatile and Air-Tolerant Platforms for Triplet–Triplet Annihilation Upconversion
Haklae Lee, Myung‐Soo Lee, Masanori Uji, Naoyuki Harada, Jeongmin Park, Jiyeon Lee, Sung Eun Seo, Chul Soon Park, Jinyeong Kim, Jinyeong Kim, Seon Joo Park, Suk Ho Bhang, Nobuhiro Yanai, Nobuo Kimizuka, Oh Seok Kwon, Jae‐Hyuk Kim, Jae‐Hyuk Kim
Abstract
Efficient and long-term stable triplet–triplet annihilation upconversion (TTA-UC) can be achieved by effectively protecting the excited organic triplet ensembles from photoinduced oxygen quenching, and discovery of a new material platform that promotes TTA-UC in ambient conditions is of paramount importance for practical applications. In this study, we present the first demonstration of an organic nonparaffin phase-change material (PCM) as an air-tolerant medium for TTA-UC with a unique solid–liquid phase transition in response to temperature variation. For the proposed concept, 2,4-hexadien-1-ol is used and extensively characterized with several key features, including good solvation capacity, mild melting point (30.5 °C), and exclusive antioxidant property, enabling a high-efficiency, low-threshold, and photostable TTA-UC system without energy-intensive degassing processes. In-depth characterization reveals that the triplet diffusion among the transient species, i.e., 3sensitizer* and 3acceptor*, is efficient and well protected from oxygen quenching in both aerated liquid- and solid-phase 2,4-hexadien-1-ol. We also propose a new strategy for the nanoencapsulation of PCM by employing hollow mesoporous silica nanoparticles as vehicles. This scheme is applicable to both aqueous- and solid-phase TTA-UC systems as well as suitable for various applications, such as thermal energy storage and smart drug delivery.