Let the light be a guide: Chromophore communication in metal-organic frameworks

The photonic characteristics of chromophore-containing metal-organic frameworks (MOFs) have led to extensive photophysical studies in an effort to capitalize on the potency of precisely controlled chromophore ensembles. Several examples have laid the foundation that demonstrates how photophysical properties of chromophores can be manipulated by tuning their communications (interactions) through integration within a MOF matrix. The main focus of this review is on harnessing the versatile MOF platform to accentuate the photophysical properties of integrated chromophores. In particular, this review will highlight chromophore dynamics that enhance, alter, or tune the photoluminescence response of single- and multi-chromophore-containing scaffolds, as well as alignment-guided anisotropic fluorescence. Building upon this groundwork, utilization of a hybrid crystalline motif can induce preferential orientation of chromophores resulting in enhanced communication and tailored behavior compared to randomly oriented emissive molecules. Moreover, frameworks that produce upconverted emission via sensitized triplet-triplet annihilation (sTTA), excited-state absorption (ESA), energy transfer upconversion (ETU), multi-photon absorption (MPA), or second-harmonic generation (SHG) can invoke dynamic control of material properties using photochromic linkers and will be discussed herein with a focus on the effects of chromophore alignment. Integration within a framework is a vehicle to fuse chromophores into solid-state platforms, opening an avenue for chromophore utilization in applications such as portable electronics that require solids or thin films. For those reasons, the design of chromophore-containing MOFs with desirable properties that rely on the alignment and communication of hundreds of chromophores within a single platform is a pressing demand for the development of futuristic technologies.