2-Azaazulenium Hemicyanine Dyes for NIR-II Multimodal Imaging and Combined Phototherapy

Hemicyanine dyes are well-defined donor-π-acceptor molecules whose photophysical and biological properties can be precisely tuned through rational molecular design. However, efficient emitters operating in the second near-infrared (NIR-II) region remain scarce, hindering their broader biomedical applications. Here, we report a strategically engineered series of 2-azaazulenium hemicyanines that achieve bright NIR-II emission together with multifunctionality. Among them, SWJT-OCH₃ integrates intense NIR-II fluorescence with outstanding photothermal and photodynamic performance, enabling multimodal imaging and combined phototherapy when encapsulated into biocompatible nanoparticles (SWJT NPs). Furthermore, an activatable probe (SWJT-Probe) derived from this platform allows highly sensitive and selective detection of peroxynitrite (ONOO^-) both in vitro and in vivo. This work establishes 2-azaazulenium hemicyanines as versatile molecular scaffolds and provides a promising design paradigm for multifunctional NIR-II fluorophores with broad biomedical potential.