Modulation of Osmium(II) Tris(2,2′-bipyridine) Photophysics through Encapsulation within Zinc(II) Trimesic Acid Metal Organic Frameworks

Abstract

The Os(II) tris(2,2′-bipyridine) (OsBpy) complex exhibits optical properties that are particularly attractive for light harvesting systems due to the broad absorption spectrum extending throughout the solar spectrum. However, the relatively short lifetime of the triplet metal to ligand charge transfer state ( 3 MLCT) relative to the related Ru(II)tris(2,2′-bipyridine) (RuBpy) has limited applications. Here, the encapsulation of OsBpy within two distinct Zn(II)-trimesic acid MOFs, HKUST-1(Zn) and USF-2 is demonstrated in an effort to extend the 3 MLCT lifetime. Encapsulation results in a hypsochromatic shift of the steady-state emission band in both frameworks resulting from a destabilization of the 3 MLCT. The encapsulated OsBpy also exhibits extended emission lifetimes in both HKUST-1(Zn) (104 ns in MOF vs 50 ns in methanol) and USF-2 (81 ns in MOF vs 50 ns in methanol) arising from changes in the nonradiative decay constants in both systems. The data are also consistent with vibronic perturbations involved in mixing between higher energy 3 MLCT* and ligand field states.

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

“…[7] In contrast, Os II polyimines do not possess thermally accessible 3 MC at room temperature while OsBpy@HKUST-1(Zn), OsBpy@USF-2, and OsPhen@HKUST-1(Zn) materials all exhibit increased emission lifetimes. [4,[6][7][8][9] The increased lifetimes have been attributed to changes in the k1/k0 ratio and ΔE which is responsible for 3 MC- 3 MLCT mixing.…”

“…The energy barrier of most Ru II complexes vary between 3000–4000 cm −1 and small increases in the barrier greatly reduce thermal access resulting in decreased lifetimes [7] . In contrast, Os II polyimines do not possess thermally accessible 3 MC at room temperature while OsBpy@HKUST‐1(Zn), OsBpy@USF‐2, and OsPhen@HKUST‐1(Zn) materials all exhibit increased emission lifetimes [4,6–9] . The increased lifetimes have been attributed to changes in the k1/k0 ratio and Δ E which is responsible for 3 MC‐ 3 MLCT mixing.…”

Synthesis, Structure, and Heterogeneous Catalysis of a Series of Structurally Diverse Coordination Polymers Based on 5-Nitroisophthalate

“…A combination of simple carboxylic acid such as 1,4-benzendicarboxylic acid − and 1,3,5-benzenetricarboxylic acid − with metal ions exhibits interesting properties. The structure of trimesic acid with 120° angular disposition between the three carboxylic acid groups along with the rigid aromatic backbone has gained attention for synthesizing various important compounds. − Substitution of one of the carboxylic acid groups with one nitro group in trimesic acid would change not only the symmetry of the moiety but also other features including hydrogen bonding acceptor site, electron-donating site, and reactivity toward metal. − By virtue of the differences offered by the ligand 5-nitroisophthalic acid (H 2 NIPA), along with the well-established scopes of CPs, H 2 NIPA in the assembly of CPs could exhibit interesting properties.…”