Defining the conditional basis of silicon phthalocyanine near-IR ligand exchange

Abstract

Bond cleavage reactions initiated by long-wavelength light are needed to extend the scope of the caged-uncaged paradigm into complex physiological settings. Axially unsymmetrical silicon phthalocyanines (SiPcs) undergo efficient release of phenol ligands in a reaction contingent on three factors - near-IR light (690 nm), hypoxia, and a thiol reductant. These studies detail efforts to define the mechanistic basis for this unique conditionally-dependent bond cleavage reaction. Spectroscopic studies provide evidence for the formation of a key phthalocyanine radical anion intermediate formed from the triplet state in a reductant-dependent manner. Computational chemistry studies indicate that phenol ligand solvolysis proceeds through a heptacoordinate silicon transition state and that this solvolytic process is favored following SiPc radical anion formation. These results provide insight regarding the central role that radical anion intermediates formed through photoinduced electron transfer with biological reductants can play in long-wavelength uncaging reactions.

Theoretical and Experimental Studies on the Near‐Infrared Photoreaction Mechanism of a Silicon Phthalocyanine Photoimmunotherapy Dye: Photoinduced Hydrolysis by Radical Anion Generation

“…The mediation of Si−O dissociation with a water molecule was also suggested by Anderson et al . for a SiPc compound with alkoxy and phenoxy ligands, further supporting the current evidence that Si−O dissociation occurs through NIR irradiation‐supported hydrolysis.…”

“…, respectively), while exhibiting very high Gibbs activation energies (209.0 and 161.8 kJ ⋅ mol −1 , respectively), which are too high to proceed at room temperature. Note that the reported activation energies of concerted ligand substitution reactions of SiPc with phenoxy ligand are 147.3 and 121.3 kJ ⋅ mol −1 for neutral and radical anion species, respectively, which are much lower than those of 2 and 2 −. , thus indicating that the concerted reaction of path (C) barely proceeds.…”

Photoinduced Ligand Release from a Silicon Phthalocyanine Dye Conjugated with Monoclonal Antibodies: A Mechanism of Cancer Cell Cytotoxicity after Near-Infrared Photoimmunotherapy

“…Additionally, if the antibody conjugate was bound to its cognate antigen, similar changes were observed (Figure g). Following this reaction, NIR-fluorescence was lost, and IR700 could not reach the triplet state; therefore, we hypothesize that no further photochemical reaction is possible at this point.…”

Visible-to-NIR-Light Activated Release: From Small Molecules to Nanomaterials

“…DFT calculations indicated that the attack of water as a nucleophile on the radical-anion center is more feasible than an attack on the neutral complex. 958 …”