MOFs for solar photochemistry applications

Photophysics of Iridium(III) (2‐phenylpyridine)(2,2’,6,2”‐terpyridine) Chloride Encapsulated within the Zinc(II) Polyhedral MOF, USF‐2

“…The excited state decay of the Ir(tpy)(ppy)Cl 2 complex in USF‐2 is quite distinct from the RuBpy@MOF systems previously examined in which the 3 MLCT decay rate significantly giving rise to much longer lifetimes of the encapsulated complex [1–6] . As discussed previously, this is due to the increase in the barrier to access the 3 LF state, the occupancy of which increases the size of the Ru complex.…”

“…Excitation at 530 nm results in formation of an 1 LLCT (L M-> L tpy M) state that relaxes rapidly to an emitting 3 LLCT. The steady-state emission data reveals only small changes in the E 00 , hω H , and S H values upon encapsulation.…”

“…The excited state decay of the Ir(tpy)(ppy)Cl 2 complex in USF-2 is quite distinct from the RuBpy@MOF systems previously examined in which the 3 MLCT decay rate significantly giving rise to much longer lifetimes of the encapsulated complex. [1][2][3][4][5][6] As discussed previously, this is due to the increase in the barrier to access the 3 LF state, the occupancy of which increases the size of the Ru complex. The results here indicate minimal excited state structural changes associated with either the 3 LLCT or the thermally accessible 3 MC state and is similar to what is observed in the Ir(ppy)(dcbpy)@Uio-67 system.…”

“…The encapsulation of homoleptic and heteroleptic Ru II polyimines such as Ru II tris-(2,2'-bipyridine) (RuBpy), Ru II tris-(1,10phenanthroline) (RuPhen), Ru II bis-(2,2'-bipyridine)(1,10-phenanthroline) (RuBpy2Phen) into most metal-organic frameworks (MOFs) generally results in extended emission lifetimes and stabilization/destabilization of the emitting triplet metal to ligand charge transfer state ( 3 MLCT). [1][2][3][4][5][6] The observed changes in the excited state lifetime are primarily due to confinement of the complex that raises the energy barrier to access a higher energy triplet metal centered ( 3 MC) state that, in turn, decays non-radiatively to the ground state with a decay constant of ~1013 s À 1 . [7] The energy barrier of most Ru II complexes vary between 3000-4000 cm À 1 and small increases in the barrier greatly reduce thermal access resulting in decreased lifetimes.…”

“…The Ir III complexes also possess a d 6 electron configuration similar to the dicatonic group 8 (Fe II , Ru II , Os II ) and the group 5 Re I complexes. [10,11] However, the homoleptic Ir(bpy) 3 3 + and Ir(tpy) 2 3 + do not exhibit visible light absorption (λ max > 400 nm) due to the generation of Ir IV in the 1 MLCT state thus limiting the use these complexes in solar photocatalytic applications. [10][11][12][13] In contrast, utilizing carbene ligands such as 2-phenylpyridine (ppy) to reduce the charge from Ir III to either Ir II or Ir I results in complexes with lower energy MLCT transitions (visible region.…”