Time-resolved terahertz spectroscopy (TRTS) of electrically conductive metal-organic frameworks (MOFs) doped with redox active species

Published: September 24, 2015

Author(s)

Brian G. Alberding, Edwin J. Heilweil

Abstract

Metal-Organic Frameworks (MOFs) are three-dimensional coordination polymers that are well known for large pore surface area and their ability to adsorb molecules from both the gaseous and solution phases. In general, MOFs are electrically insulating, but promising opportunities for tuning the electronic structure exist because MOFs possess synthetic versatility; the metal and organic ligand subunits can be exchanged or dopant molecules can be introduced into the pore space. Two such MOFs with demonstrated electrical conductivity are Cu3(1,3,5-benzenetricarboxylate)2, a.k.a HKUST-1, and Cu[Ni(pyrazine-2,3-dithiolate)2]. Herein, these two MOFs have been infiltrated with the redox active species 7,7,8,8-tetracyanoquinodimethane (TCNQ) and iodine under solution phase conditions and shown to produce redox products within the MOF pore space. Vibrational bands assignable to TCNQ anion and triiodide anion have been observed in the Mid-IR and Terahertz ranges using FTIR Spectroscopy. The MOF samples have been further investigated by Time-Resolved Terehertz Spectroscopy (TRTS). Using this technique, the charge mobility, separation, and recombination dynamics have been followed on the picosecond time scale following photoexcitation with visible radiation. The preliminary results show that the MOF samples have small inherent photoconductivity with charge separation lifetimes on the order of a few picoseconds. In the case of HKUST-1, the MOF can also be supported by a TiO2 film and initial results show that charge injection into the TiO2 layer occurs with a comparable efficiency to the N3 dye sensitizer and therefore this MOF has potential as a new light absorbing and charge conducting material in photovoltaic devices.
Proceedings Title: SPIE Optics and Photonics 2015
Volume: 9567
Conference Dates: August 9-13, 2015
Conference Location: San Diego, CA
Conference Title: Organic Photonics and Electronics
Pub Type: Conferences

Keywords

metal-organic framework, time-resolved terahertz spectroscopy, HKUST-1, charge carrier dynamics, photoconductivity, picosecond
Created September 24, 2015, Updated February 19, 2017