Enhanced type I photoreaction of indocyanine green via electrostatic-force-driven aggregation

Abstract

ICG forms aggregates in positively charged mesoporous silica, which show an enhanced type I photoreaction pathway.

Deuterated Indocyanine Green (ICG) with Extended Aqueous Storage Shelf‐Life: Chemical and Clinical Implications

“…This picture of aggregation‐dependent reactivity is supported by experiments in organic solvents, such as ethanol, where there is negligible ICG self‐aggregation and very little oxidative dimerization (Figure S28a). There is also recent literature evidence that self‐aggregation in water promotes photoinduced electron transfer from ICG to molecular oxygen [53] The first two steps in the proposed photosensitized oxidative dimerization mechanism in Scheme 4c involve reversible electron transfer from excited triplet state ICG to dissolved molecular oxygen to produce a superoxide radical anion and ICG radical cation, followed by reversible attack of the radical cation on a second ICG molecule [23,27,47,53–56] .…”

“…This picture of aggregation‐dependent reactivity is supported by experiments in organic solvents, such as ethanol, where there is negligible ICG self‐aggregation and very little oxidative dimerization (Figure S28a). There is also recent literature evidence that self‐aggregation in water promotes photoinduced electron transfer from ICG to molecular oxygen [53] …”

“…There is also recent literature evidence that self‐aggregation in water promotes photoinduced electron transfer from ICG to molecular oxygen. [53] The first two steps in the proposed photosensitized oxidative dimerization mechanism in Scheme 4 c involve reversible electron transfer from excited triplet state ICG to dissolved molecular oxygen to produce a superoxide radical anion and ICG radical cation, followed by reversible attack of the radical cation on a second ICG molecule. [ 23 , 27 , 47 , 53 , 54 , 55 , 56 ] Subsequent proton abstraction is an irreversible third step that is slowed in [D 5 ]‐ ICG (and also in [D 7 ]‐ ICG ) because the activation energy for deuteron abstraction is higher.…”

“… [53] The first two steps in the proposed photosensitized oxidative dimerization mechanism in Scheme 4 c involve reversible electron transfer from excited triplet state ICG to dissolved molecular oxygen to produce a superoxide radical anion and ICG radical cation, followed by reversible attack of the radical cation on a second ICG molecule. [ 23 , 27 , 47 , 53 , 54 , 55 , 56 ] Subsequent proton abstraction is an irreversible third step that is slowed in [D 5 ]‐ ICG (and also in [D 7 ]‐ ICG ) because the activation energy for deuteron abstraction is higher. These three steps rationalize the observed deuterium kinetic isotope effect of 3.1 and also the observed second order dependence on [ ICG ] (see Figure S30 for expanded kinetic expression).…”

“…From a broader biomedical perspective, the results of this study suggest additional future research directions for pursuit. For example, the idea that self‐aggregation of amphiphilic cyanine dyes, like ICG , can promote photoinduced electron transfer chemistry has been recognized by dye chemists for some time, [63] but has not yet been fully exploited as a rational design paradigm for next‐generation photodynamic therapy [53,64] . Likewise, deuterated polymethine cyanine dyes with a low propensity for photooxidative dimerization are promising future candidates for optimized super‐resolution microscopy [65]…”