Photophysical Studies of Ru(II)tris(2,2′-bipyridine) Confined within a Zn(II)–Trimesic Acid Polyhedral Metal–Organic Framework

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,
the confinement of Ru­(II)­tris­(2,2′-bipyridine) (RuBpy) by a
MOF material derived from Zn­(II) ions and trimesic acid (hereafter,
USF2) is examined. Although the encapsulated RuBpy could not be crystallographically
resolved within the MOF framework, the photophysical properties of
the complex are characteristic of confinement including extended triplet
metal-to-ligand (3MLCT) lifetime (τethanol = 614 ns and τUSF2 = 1.2 μs at 25 °C)
and a slight hypsochromic shift in the steady-state emission spectrum
relative to RuBpy in ethanol. The extended lifetime is attributed
to a deactivation of a nonradiative 3dd that is antibonding
with respect to the Ru­(II)-bipyridine due to a confined molecular
environment. These results represent one of the first examples of
RuBpy encapsulation and photophysical characterization within a polyhedral
MOF material.