RESUMEN
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.
RESUMEN
Porphyrin based metal organic frameworks (MOFs) have provided a broad platform through which a wide variety of light harvesting applications have been developed. Of particular interest within light harvesting MOFs containing porphyrin chromophores is the extent to which the both environment of the porphyrin and the porphyrin conformation modulate the photophysical properties. With this in mind, a new MOF (RWLAA-1) has been synthesized based on zinc cations linked by zinc(ii) tetra(4-pyridyl)porphyrin (ZnTPyP) and benzene tricarboxylate (H3BTC) linkers in which the porphyrin exhibits significant conformational distortions that have a profound effect on the photophysics of the material including bathochromic shifts in both the optical (Soret and visible bands) and emission bands, reduction in the energy separation between the Q(0,0) and Q(0,1) emission bands and shorter singlet and triplet state lifetimes. These effects are consistent with the porphyrin deformation resulting in changes in the porphyrin electronic structure and excited state conformational dynamics that alter the vibronic coupling between the excited states (S1 and T1) and the S0 ground state.
RESUMEN
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.
RESUMEN
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 â¼38% of the encapsulated RuBpy complexes resulting in the nonradiative deactivation of the 3MLCT state.
