Engineering of Electrochromic Materials as Activatable Probes for Molecular Imaging and Photodynamic Therapy

Electrochromic materials (EMs) are
widely used color-switchable
materials, but their applications as stimuli-responsive biomaterials
to monitor and control biological processes remain unexplored. This
study reports the engineering of an organic π-electron structure-based
EM (dicationic 1,1,4,4-tetra­aryl­buta­diene, 12+) as a unique hydrogen sulfide (H2S)-responsive chromophore amenable to build H2S-activatable
fluorescent probes (12+-semiconducting polymer
nanoparticles, 12+-SNPs) for in vivo
H2S detection. We demonstrate that EM 12+, with a strong absorption (500–850 nm), efficiently
quenches the fluorescence (580, 700, or 830 nm) of different fluorophores
within 12+-SNPs, while the selective conversion
into colorless diene 2 via H2S-mediated two-electron
reduction significantly recovers fluorescence, allowing for non-invasive
imaging of hepatic and tumor H2S in mice in real time.
Strikingly, EM 12+ is further applied to design
a near-infrared photosensitizer with tumor-targeting and H2S-activatable ability for effective photodynamic therapy (PDT) of
H2S-related tumors in mice. This study demonstrates promise
for applying EMs to build activatable probes for molecular imaging
of H2S and selective PDT of tumors, which may lead to the
development of new EMs capable of detecting and regulating essential
biological processes in vivo.