Ruthenium(II) Tris(2,2′-bipyridine)-Templated Zinc(II) 1,3,5-Tris(4-carboxyphenyl)benzene Metal Organic Frameworks: Structural Characterization and Photophysical Properties

The
ability to confine photoactive catalysts within metal organic
framework (MOF) materials affords the opportunity to expand the functional
diversity of these materials into solar-based applications. Here,
two new Ru­(II) tris­(2,2′-bipyridine) (RuBpy)-based photoactive
materials derived from reactions between Zn­(II) ions and 1,3,5-tris­(4-carboxyphenyl)­benzene
and templated by the presence of RuBpy (RWLC-1 and RWLC-2) are described
with regard to structure and RuBpy photophysics. RuBpy cations have
been successfully encapsulated within the cavities (RWLC-1) and channels
(RWLC-2) of the new negatively charged frameworks, both of which are
synthesized simultaneously in a single reaction vial. Single-crystal
X-ray diffraction studies allowed for determination of the RuBpy position
within crystal voids. RuBpy encapsulated in each of the two new MOFs
exhibits biphasic triplet metal to ligand charge transfer (3MLCT) emission decay lifetimes (τRWLC‑1‑fast = 237 ns, τRWLC‑1‑slow = 1.60 μs,
τRWLC‑2‑fast = 171 ns, and τRWLC‑2‑slow = 797 ns at 25 °C) consistent
with two populations of RuBpy complexes, one being encapsulated in
highly space-restricted cavities giving rise to a longer 3MLCT lifetime, while the second is encapsulation within a larger
nonperiodic pore or defect with a coencapsulated quencher giving rise
to short emission lifetimes. Taken together, these results represent
examples of the templating ability of RuBpy to produce novel materials
with distinct photophysical environments of the encapsulated guests.