pubs.acs.org
Breaking Bonds with Short-Wave Infrared Light: BODIPY Photocages for Two-Photon Activation in the 900–1500 nm NIR-II Window
Photocages enable light-triggered cargo release in biological systems, but their excitation is often restricted to UV/visible wavelengths, where tissue penetration is limited. Two-photon excitation (2PE) offers a solution by allowing near-infrared (NIR) or short-wave infrared (SWIR) activation within biological windows of maximal tissue transparency. While photocaging in the first biological window (650–950 nm) has been demonstrated, applications in the second biological window (1000–1350 nm) remain unexplored. Here, we investigate the two-photon absorption (2PA) properties of 11 BODIPY photocages featuring single-photon absorption spanning 450–750 nm, focusing on 3- and 5-position substitutions to identify key motifs that enhance 2PA in the 900–1500 nm range. We find that strong charge transfer character and increased vibrational freedom can relax symmetry-related selection rules, significantly enhancing 2PA. Cross sections (δ) exceeded 4000 GM at 900 nm for a bis(styryl)-BODIPY with carbazole units and reached 1110 GM at 1240 nm for its monostyryl analog. Two additional B-methylated molecules with improved uncaging quantum yields were synthesized, yielding uncaging action cross sections (δΦu) up to 5.8 GM at 900 nm and around 1 GM at 1300–1400 nm. Notably, these modifications preserve the core photophysical properties of BODIPY, making them ideal for molecular engineering. These findings highlight key design principles for efficient 2P-activatable photoactuators operating in the NIR-II biological window and show that heterolytic C–O bond cleavage can be triggered by two SWIR photons carrying as little as 20 kcal/mol each.
