Hetero-bichromophore Dyad as a Highly Efficient Triplet Acceptor for Polarity Tuned Triplet-Triplet Annihilation Upconversion

Recent progress in upconversion nanomaterials for emerging optical biological applications

The recent advances of upconversion nanoparticles (UCNPs) have made them the ideal "partner" for a variety of biological applications. In this review, we describe the emerging biological optical applications of UCNPs, focus on their potential therapeutic advantages. Firstly, we briefly review the development and mechanisms of upconversion luminescence, including organic and inorganic UCNPs. Next, in the section on UCNPs for imaging and detection, we list the development of UCNPs in visualization, temperature sensing, and detection. In the section on therapy, recent results are described concerning optogenetics and neurotherapy. Tumor therapy is another major part of this section, including the synergistic application of phototherapy such as photoimmunotherapy. In a special section, we briefly cover the integration of UCNPs in therapeutics. Finally, we present our understanding of the limitations and prospects of applications of UCNPs in biological fields, hoping to provide a more comprehensive understanding of UCNPs and attract more attention.

Triplet-triplet annihilation upconversion with reversible emission-tunability induced by chemical-stimuli: a remote modulator for photocontrol isomerization

Triplet-triplet annihilation upconversion (TTA-UC) has been widely studied, but a color-tunable TTA-UC system triggered by chemical stimuli has not yet been proposed. Herein, reversible acid/base switching of the TTA-UC emission wavelength is achieved for the first time by a simple platform, composed of a direct singlet-triplet (S₀-T₁) absorption photosensitizer, and proton-responsive 9,10-di(pyridin-4-yl)anthracene (DPyA) as an acceptor. The photosensitizer-acceptor pair exhibits efficient UC emission (quantum yield up to 3.3%, and anti-Stokes shift up to 0.92 eV) with remarkable contrast upon base/acid treatment (Δλ_em,max = 82 nm, 0.46 eV). In a proof-of-concept study, the color-adjustable TTA-UC emission was applied as a remote modulator to photo-control reversible chemical reactions for the first time. This platform enriches the portfolio of color-switchable TTA-UC, and the mechanism would inspire further development of smart UC systems and extend the application field of upconversion.

Trapped excited electrons in Ni2+-doped perovskite KZnF3 nanocrystals in KF-ZnF2-SiO2 glass ceramics

The photonic properties of glass ceramics (GCs) are often enabled by encapsulating nanocrystals (NCs) and doped transition metal ions (TMIs). However, it is difficult to probe the optics-related effect between the host NCs' band structure and doped TMIs' d-d orbitals. Herein, perovskite-type KZnF₃:NiNCs in KF-ZnF₂-SiO₂ GCs were prepared and taken as a model system. The excited-state dynamics of host NCs and Ni ions' d-d orbitals were studied by transient absorption spectroscopy. It presents a strong interaction between Ni's d orbitals and the band edge, which could extract excitonic energy in photonic applications. These findings facilitate understanding and design of TMIs-doped GCs in real-life photonic applications.