Light-Harvesting Cross-Linked
Polymers for Efficient
Heterogeneous Photocatalysis
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Abstract
Nonporous, phosphorescent cross-linked polymers (<b>Ru-CP</b> and <b>Ir-CP</b>) were synthesized via Pd-catalyzed
Sonogashira
cross-coupling reactions between tetra(<i>p</i>-ethynylphenyl)methane
and dibrominated Ru(bpy)<sub>3</sub><sup>2+</sup> or Ir(ppy)<sub>2</sub>(bpy)<sup>+</sup>, respectively. The resultant particulate cross-linked polymer
(CP) materials have very high catalyst loadings (76.3 wt %
for <b>Ru-CP</b> and 71.6 wt % for <b>Ir-CP</b>), and are nonporous with negligibly small surface areas (2.9 m<sup>2</sup>/g for <b>Ru-CP</b> and 2.7 m<sup>2</sup>/g for <b>Ir-CP</b>). Despite their nonporous nature, the insoluble CP materials
serve as highly active and recyclable heterogeneous photocatalysts
for a range of organic transformations such as aza-Henry reaction,
aerobic amine coupling, and dehalogenation of benzyl bromoacetate.
An efficient light-harvesting mechanism, which involves collection
of photons by exciting the <sup>3</sup>MLCT states of the phosphors
and migration of the excited states to the particle surface, is proposed
to account for the very high catalytic activities of these nonporous
CPs. Steady-state and time-resolved emission data, as well as the
reduced catalytic activity of Os(bpy)<sub>3</sub><sup>2+</sup>-doped <b>Ru-CP</b>s supports efficient excited state migration for the CP
frameworks. This work uncovers a new strategy in designing highly
efficient photocatalysts based on light-harvesting cross-linked polymers