decay rate (emission decay rate) is on the order of ~600 ns in deaerated solution and
is sensitive to both temperature and solvent. A metal-centered ligand field state (
3 LF)
can also be thermally populated from the lower-energy
3 MLCT manifold through an
energy barrier of ~3,500 cm
À1 . The
3 LF state has antibonding with respect to the
Ru-N bonds and decays non-radiatively with a fast decay constant of
~1 Â 10
13 s
À1 [41].
2 Ruthenium(II) Polyimines as Photoactive Guests Within
Zn-Based Polyhedral MOFs
2.1 Zn-Carboxylate-Based Polyhedral MOFs
Zinc(II) carboxylate MOFs are a class of porous materials composed of polyhedral
cages which share common vertices and windows into adjacent cavities. A wide
variety of Zn(II) and Cu(II) polyhedral MOFs have been synthesized and characterized and are one of the earliest examples of reticular porous materials. Among the
most widely known polyhedral MOFs are the IRMOFs developed by Omar Yaghi
[42]. The IRMOF series share a common cubic topology constructed from linear
organic linkers of various sizes linking Zn oxide clusters. The isoreticular approach
allows for the development of frameworks that includes a wide range of cavity and
window diameters [43, 44]. Another polyhedral framework, while not originally
synthesized with Zn(II) ions, is HKUST-1 whose Zn analog has shown promising
properties in the development of photocatalytic materials. The HKUST-1 framework
was among the first nanoporous materials with regard to crystallinity which could be
chemically functionalized unlike the more widely utilized inorganic zeolites
[45]. The HKUST-1 topology incorporates Cu-Cu paddle wheel MBBs which are
a common building unit in high-performing multifunctional materials including
NU-111 [46], PCN-14 [47], and NOTT-115 [48]. The HKUST-1(Zn) framework
is isostructural with HKUST-1(Cu) and is composed of dinuclear Zn(II) paddle
wheel MBBs connected from benzene-1,3,5-dicarboxylate (BTCA) to form a
3,4-connected cubic framework (tbo – net topology) [31, 45]. The HKUST-1(Zn)
contains three cavities whose shapes can be approximated as rhombihexahedron of
13 Å diameter (1,278 Å
3 volume), octahemioctahedron of 11 Å diameter (696 Å
3
volume), and tetrahedron of 5 Å diameter (65 Å
3 volume). Another topology
isostructural with HKUST-1(Zn) is USF2 which is a polyhedral MOF composed
of dinuclear Zn-paddle wheel MBBs also connected through trimesic acid linkers
resulting in a Pm-3m cubic symmetry [49]. The resulting framework can be viewed
as a tiling of 3D space with two faceted polyhedrals (cuboctahedron and
octahemioctahedron) with an edge skeleton cube. The largest cavity in USF2 can
be viewed as a cuboctahedron with diameter of ~15 Å with small windows of ~9 Å.
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R. W. Larsen et al.
is sensitive to both temperature and solvent. A metal-centered ligand field state (
3 LF)
can also be thermally populated from the lower-energy
3 MLCT manifold through an
energy barrier of ~3,500 cm
À1 . The
3 LF state has antibonding with respect to the
Ru-N bonds and decays non-radiatively with a fast decay constant of
~1 Â 10
13 s
À1 [41].
2 Ruthenium(II) Polyimines as Photoactive Guests Within
Zn-Based Polyhedral MOFs
2.1 Zn-Carboxylate-Based Polyhedral MOFs
Zinc(II) carboxylate MOFs are a class of porous materials composed of polyhedral
cages which share common vertices and windows into adjacent cavities. A wide
variety of Zn(II) and Cu(II) polyhedral MOFs have been synthesized and characterized and are one of the earliest examples of reticular porous materials. Among the
most widely known polyhedral MOFs are the IRMOFs developed by Omar Yaghi
[42]. The IRMOF series share a common cubic topology constructed from linear
organic linkers of various sizes linking Zn oxide clusters. The isoreticular approach
allows for the development of frameworks that includes a wide range of cavity and
window diameters [43, 44]. Another polyhedral framework, while not originally
synthesized with Zn(II) ions, is HKUST-1 whose Zn analog has shown promising
properties in the development of photocatalytic materials. The HKUST-1 framework
was among the first nanoporous materials with regard to crystallinity which could be
chemically functionalized unlike the more widely utilized inorganic zeolites
[45]. The HKUST-1 topology incorporates Cu-Cu paddle wheel MBBs which are
a common building unit in high-performing multifunctional materials including
NU-111 [46], PCN-14 [47], and NOTT-115 [48]. The HKUST-1(Zn) framework
is isostructural with HKUST-1(Cu) and is composed of dinuclear Zn(II) paddle
wheel MBBs connected from benzene-1,3,5-dicarboxylate (BTCA) to form a
3,4-connected cubic framework (tbo – net topology) [31, 45]. The HKUST-1(Zn)
contains three cavities whose shapes can be approximated as rhombihexahedron of
13 Å diameter (1,278 Å
3 volume), octahemioctahedron of 11 Å diameter (696 Å
3
volume), and tetrahedron of 5 Å diameter (65 Å
3 volume). Another topology
isostructural with HKUST-1(Zn) is USF2 which is a polyhedral MOF composed
of dinuclear Zn-paddle wheel MBBs also connected through trimesic acid linkers
resulting in a Pm-3m cubic symmetry [49]. The resulting framework can be viewed
as a tiling of 3D space with two faceted polyhedrals (cuboctahedron and
octahemioctahedron) with an edge skeleton cube. The largest cavity in USF2 can
be viewed as a cuboctahedron with diameter of ~15 Å with small windows of ~9 Å.
160
R. W. Larsen et al.