Dominant Role of Hole Transport Pathway in Achieving Record High Photoconductivity in Two-Dimensional Metal-Organic Frameworks.

Metal-organic frameworks (MOFs) with mobile charges have attracted significant attention due to their potential applications in photoelectric devices, chemical resistance sensors, and catalysis. However, fundamental understanding of the charge transport pathway within the framework and the key properties that determine the performance of conductive MOFs in photoelectric devices remain underexplored. Herein, we report the mechanisms of photoinduced charge transport and electron dynamics in the conductive 2D M-HHTP (M=Cu, Zn or Cu/Zn mixed; HHTP=2,3,6,7,10,11-hexahydroxytriphenylene) MOFs and their correlation with photoconductivity using the combination of time-resolved terahertz spectroscopy, optical transient absorption spectroscopy, X-ray transient absorption spectroscopy, and density functional theory (DFT) calculations.

Engineering Band Gap and Photoconduction in Semiconducting Metal Organic Frameworks: Metal Node Effect.

We report a systematic study on the correlation of the metal nodes in M-THQ conducting MOFs (M = Fe, Ni, Cu, and Zn; THQ = tetra-hydroxybenzoquinone) with their structure, photophysical property, and photoconductivity. We found that the structural preference in these MOFs is controlled by metal node identity where Cu prefers a square planar coordination which leads to a 2D Kagome-type structure. Fe, Ni, and Zn prefer an octahedral sphere which leads to a 3D structure.

Interrogating Light-initiated Dynamics in Metal-Organic Frameworks with Time-resolved Spectroscopy.

Time-resolved spectroscopy is an essential part of both fundamental and applied chemical research. Such techniques access light-initiated dynamics on time scales ranging from femtosecond to microsecond. Many techniques falling under this description have been applied to gain significant insight into metal-organic frameworks (MOFs), a diverse class of porous coordination polymers.

A conductive metal-organic framework photoanode.

We report the development of photosensitizing arrays based on conductive metal-organic frameworks (MOFs) that enable light harvesting and efficient charge separation. ZnTTFTB (TTFTB = tetrathiafulvalene tetrabenzoate) MOFs are deposited directly onto TiO photoanodes and structurally characterized by pXRD and EXAFS measurements. Photoinduced interfacial charge transfer dynamics are investigated by combining time-resolved THz spectroscopy and quantum dynamics simulations.

Direct Evidence of Photoinduced Charge Transport Mechanism in 2D Conductive Metal Organic Frameworks.

Conductive metal organic frameworks (MOFs) represent a promising class of porous crystalline materials that have demonstrated potential in photo-electronics and photocatalytic applications. However, the lack of fundamental understanding on charge transport (CT) mechanism as well as the correlation of CT mechanism with their structure hampered their further development. Herein, we report the direct evidence of CT mechanism in 2D Cu-THQ MOFs and the correlation of temporal and spatial behaviors of charge carriers with their photoconductivity by combining three advanced spectroscopic methods, including time resolved optical and X-ray absorption spectroscopy and terahertz spectroscopy.

Suspensions of Semiconducting Nanoparticles in Nafion for Transient Spectroscopy and Terahertz Photoconductivity Measurements.

The characterization of emerging materials is crucial for the experimentally driven design of next-generation technologies. We describe a cost- and time-effective method for suspending nanoparticles and other photoactive materials in Nafion for transient spectroscopy and time-resolved terahertz (THz) photoconductivity measurements. Nafion is an ideal suspension matrix because it has high transparency throughout the UV/vis/near-IR and THz regions of the spectrum.

Metal-Organic Framework Photoconductivity via Time-Resolved Terahertz Spectroscopy.

While metal-organic frameworks (MOFs) have been under thorough investigation over the past two decades, photoconductive MOFs are an emerging class of materials with promising applications in light harvesting and photocatalysis. To date, there is not a general method to investigate the photoconductivity of polycrystalline MOF samples as-prepared. Herein, we utilize time-resolved terahertz spectroscopy along with a new sample preparation method to determine the photoconductivity of ZnTTFTB, an archetypical conductive MOF, in a noncontact manner.

Controlling Proton Conductivity with Light: A Scheme Based on Photoacid Doping of Materials.

Transducing light energy to changes in material properties is central to a large range of functional materials, including those used in light harvesting. In conventional semiconductors, photoconductivity arises due to generation of mobile electrons or holes with light. Here we demonstrate, to our knowledge for the first time, an analogue of this effect for protons in an organic polymer solution and in water.