Photophysical properties of [Ru(2,2′-bipyridine) 3 ] 2+ encapsulated within the Uio-66 zirconium based metal organic framework

Visible light-driven oxidation of non-native substrate by laccase attached on Ru-based metal-organic frameworks

Light-induced electron transfer can broaden the substrate range of metalloenzyme. However, the efficiency of photo-enzyme coupling is limited by the poor combination of photosensitizer or photocatalyst with enzyme. Herein, we prepared the nano-photocatalyst MIL-125-NH2@Ru(bpy) by in site embedding ruthenium pyridine-diimine complex [Ru(bpy)3]2+ into metal organic frameworks MIL-125-NH2 and associated it with multicopper oxidase (MCO) laccase. Compared to [Ru(bpy)3]2+, the coupling efficiency of MIL-125-NH2@Ru(bpy)3 for enzymatic oxygen reduction increased by 35.7%. A series of characterizations confirmed that the amino group of laccase formed chemical bonds with the surface defects or hydrophobic groups of MIL-125-NH2@Ru(bpy)3. Consequently, the tight binding accelerated the quenching process and electron transfer between laccase and the immobilized ruthenium pyridine-diimine complex. This work would open an avenue for the synthesis of MOFs photocatalyst towards photo-enzyme coupling.

Surface Ru-H Bipyridine Complexes-Grafted TiO2 Nanohybrids for Efficient Photocatalytic CO2 Methanation

A series of novel surface Ru-H bipyridine complexes-grafted TiO₂ nanohybrids were for the first time prepared by a combined procedure of surface organometallic chemistry with post-synthetic ligand exchange for photocatalytic conversion of CO₂ to CH₄ with H₂ as electron and proton donors under visible light irradiation. The selectivity toward CH₄ increased to 93.4% by the ligand exchange of 4,4'-dimethyl-2,2'-bipyridine (4,4'-bpy) with the surface cyclopentadienyl (Cp)-RuH complex and the CO₂ methanation activity was enhanced by 4.4-fold. An impressive rate of 241.2 μL·g^-1·h^-1 for CH₄ production was achieved over the optimal photocatalyst. The femtosecond transient IR absorption results demonstrated that the hot electrons were fast injected in 0.9 ps from the photoexcited surface 4,4'-bpy-RuH complex into the conduction band of TiO₂ nanoparticles to form a charge-separated state with an average lifetime of ca. 50.0 ns responsible for the CO₂ methanation. The spectral characterizations indicated clearly that the formation of CO₂^•- radicals by single electron reduction of CO₂ molecules adsorbed on surface oxygen vacancies of TiO₂ nanoparticles was the most critical step for the methanation. Such radical intermediates were inserted into the explored Ru-H bond to generate Ru-OOCH species and finally CH₄ and H₂O in the presence of H₂.

Confinement of Luminescent Guests in Metal–Organic Frameworks: Understanding Pathways from Synthesis and Multimodal Characterization to Potential Applications of LG@MOF Systems

This review gives an authoritative, critical, and accessible overview of an emergent class of fluorescent materials termed “LG@MOF”, engineered from the nanoscale confinement of luminescent guests (LG) in a metal–organic framework (MOF) host, realizing a myriad of unconventional materials with fascinating photophysical and photochemical properties. We begin by summarizing the synthetic methodologies and design guidelines for representative LG@MOF systems, where the major types of fluorescent guest encompass organic dyes, metal ions, metal complexes, metal nanoclusters, quantum dots, and hybrid perovskites. Subsequently, we discuss the methods for characterizing the resultant guest–host structures, guest loading, photophysical properties, and review local-scale techniques recently employed to elucidate guest positions. A special emphasis is paid to the pros and cons of the various methods in the context of LG@MOF. In the following section, we provide a brief tutorial on the basic guest–host phenomena, focusing on the excited state events and nanoscale confinement effects underpinning the exceptional behavior of LG@MOF systems. The review finally culminates in the most striking applications of LG@MOF materials, particularly the “turn-on” type fluorochromic chemo- and mechano-sensors, noninvasive thermometry and optical pH sensors, electroluminescence, and innovative security devices. This review offers a comprehensive coverage of general interest to the multidisciplinary materials community to stimulate frontier research in the vibrant sector of light-emitting MOF composite systems.

[Ru(bpy)3]2+@Ce-UiO-66/Mn:Bi2S3 Heterojunction and Its Exceptional Photoelectrochemical Aptasensing Properties for Ofloxacin Detection

A photoelectrochemical (PEC) aptasensor on basis of [Ru(bpy)₃]²⁺@Ce-UiO-66/Mn:Bi₂S₃ composites was constructed for detecting ofloxacin (OFL). First, Ce-UiO-66, prepared by a solvothermal method, had Zr⁴⁺-Zr³⁺ and Ce⁴⁺-Ce³⁺ intervalence cycles to increase the charge separation efficiency. Subsequently, Ce-UiO-66 was further modified by [Ru(bpy)₃]²⁺ and Mn:Bi₂S₃ cosensitization to improve the photoelectric activity. [Ru(bpy)₃]²⁺ not only broadened the range of light absorbed but also reacted with an electron donor to maintain the photoelectric conversion process. Among the [Ru(bpy)₃]²⁺@Ce-UiO-66/Mn:Bi₂S₃ heterojunction, Mn:Bi₂S₃ was a photosensitizer, which maximized the efficiency of the electron-hole separation and significantly improved photocurrent. Then, an aptamer was used as a biorecognition unit for OFL-specific detection. Under the best conditions, the PEC aptasensor realized the sensitive detection of OFL, with a detection range of 0.01-100 nmol/L and a detection limit of 6 pmol/L. In addition, the constructed PEC OFL sensor showed good reproducibility, stability, and specificity.

Confinement-guided photophysics in MOFs, COFs, and cages

In this review, the dependence of the photophysical response of chromophores in the confined environments associated with crystalline scaffolds, such as metal-organic frameworks (MOFs), covalent-organic frameworks (COFs), and molecular cages, has been carefully evaluated. Tunability of the framework aperture, cavity microenvironment, and scaffold topology significantly affects emission profiles, quantum yields, or fluorescence lifetimes of confined chromophores. In addition to the role of the host and its effect on the guest, the methods for integration of a chromophore (e.g., as a framework backbone, capping linker, ligand side group, or guest) are discussed. The overall potential of chromophore-integrated frameworks for a wide-range of applications, including artificial biomimetic systems, white-light emitting diodes, photoresponsive devices, and fluorescent sensors with unparalleled spatial resolution are highlighted throughout the review.

Heterogenisation of polyoxometalates and other metal-based complexes in metal–organic frameworks: from synthesis to characterisation and applications in catalysis

This review provides a thorough overview of composites with molecular catalysts (polyoxometalates, or organometallic or coordination complexes) immobilised into MOFs via non-covalent interactions.

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

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 (³MLCT) 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 ³MLCT lifetime. Encapsulation results in a hypsochromatic shift of the steady-state emission band in both frameworks resulting from a destabilization of the ³MLCT. 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 ³MLCT* and ligand field states.

Incorporation of a Ru complex into an amine-functionalized metal–organic framework for enhanced activity in photocatalytic aerobic benzyl alcohol oxidation

Encapsulation of [Ru(bpy)₃]²⁺ in the cavity of a metal–organic framework was found to enhance its activity in the photocatalytic aerobic oxidation of benzyl alcohol.

Guest to framework photoinduced electron transfer in a cobalt substituted RWLC-2 metal organic framework

Photoinduced electron transfer (PET) between donors and acceptors in porous materials is a key element in the development of light harvesting applications. Metal organic frameworks (MOFs) are ideal materials for PET processes due to their tunable pore size and diversity in framework building units. Here, PET between excited [Ru(2,2'-bipyridine)3]2+ (RuBpy) and Co-carboxylate clusters composing the metal building blocks of a RWLC-2 metal organic framework is described. The lifetime of the RuBpy decreases from ∼600 ns in deaerated solution to 9.5 ns (kET ∼ 1 × 108 s-1) when encapsulated within CoRWLC-2. The decrease in lifetime is attributed to PET between the 3MLCT of RuBpy to the Co ion cluster composing the MOF building blocks. A fit of the lifetime vs. temperature data to the semi-empirical Marcus equation gives a reorganizational energy of 1.6 eV and an electronic coupling factor (HAB) of 0.006 eV.

A novel photo-active Cd:1,4-benzene dicarboxylate metal organic framework templated using [Ru(ii)(2,2'-bipyridine)3]2+: synthesis and photophysics of RWLC-5

The development of photoactive porous materials is of significant importance for applications ranging from sustainable energy to pharmaceutical development and catalysis. A particularly attractive class of photo-active materials is the metal-organic framework (MOF)-based platform in which the photo-active elements are components of the framework itself or photo-active guests encapsulated within the MOF cavities. It has now been demonstrated that the photo-active [Ru(2,2'-bipyridine)₃]²⁺ (RuBpy) complex can template the formation of MOFs with varying three dimensional structures. Here we report the synthesis and structural and photo-physical characterization of a new RuBpy-templated MOF composed of Cd²⁺ ions with 1,4-benzenedicarboxylate ligands (RWLC-5) that contains crystallographically resolved RuBpy complexes. The new material displays a biphasic emission decay (130 ns and 1180 ns, T = 20 °C) and a bathochromically shifted emission maximum, relative to RuBpy in solution (603 nm for RuBpy in ethanol vs. 630 nm for RWLC-5). The emission lifetimes also do not display temperature-dependent decays which are characteristic of RuBpy type complexes as well as other RuBpy templated MOFs. The lack of temperature dependence is consistent with the complete deactivation of the ³LF state of the encapsulated RuBpy complex due to a constrained environment. The fast phase decay is attributed to a water molecule hydrogen bonded to a bipyridine ligand associated with ∼38% of the encapsulated RuBpy complexes resulting in the nonradiative deactivation of the ³MLCT state.