Direct Observation of Node-to-Node Communication in Zeolitic Imidazolate Frameworks

Abstract

Zeolitic imidazolate frameworks (ZIFs) with open-shell transition metal nodes represent a promising class of highly ordered light harvesting antennas for photoenergy applications. However, their charge transport properties within the framework, the key criterion to achieve efficient photoenergy conversion, are not yet explored. Herein, we report the first direct evidence of a charge transport pathway through node-to-node communication in both ground state and excited state ZIFs using the combination of paramagnetic susceptibility measurements and time-resolved optical and X-ray absorption spectroscopy. These findings provide unprecedented new insights into the photoactivity and charge transport nature of ZIF frameworks, paving the way for their novel application as light harvesting arrays in diverse photoenergy conversion devices.

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

“…In addition, the OTA spectra of Zn-THQ (Figure S4b) also show very distinct features from that of Cu-THQ, where a much sharper negative band at 570 nm and two well-defined positive features centered at 520 and 625 nm were observed in the spectra of Zn-THQ. Given that the Zn 2+ node with closed shell 3d 10 electron configuration is anticipated to prevent the ligand-M-ligand through-bond CT pathway in Zn-THQ, 29 the spectral evolutions in the OTA spectra of Cu-THQ are likely due to the delocalized intralayer excitons which transport via through-bond pathway. The OTA spectra of Cu/ Zn-THQ (Figure 2c) show similar spectral shape (EB, E1, and E2) as that of Cu-THQ.…”

“…The XTA experiment was performed at beamline 11-ID-D at APS and is described in our earlier report. 29 Briefly, 400 nm optical pump pulses were produced by a commercial regeneratively amplified Ti:Sapphire laser: a 3 kHz, 100 fs (FWHM), 3.3 mJ, 800 nm pulse train, which was produced by a Legend Elite Duo amplifier system seeded by a Micra-5 oscillator and pumped by an Evolution intracavity-doubled, diode pumped Nd:YLF Q-switched laser. The 800 nm signal output was then doubled with a BBO crystal to produce 400 nm laser pulse.…”

“…In response to these challenges, herein, we report the study of the CT mechanism in 2D MOFs constructed from Cu nodes connected by tetrahydroxyquinone (THQ), aiming for the direct correlation of both spatial and temporal behaviors of charge carriers with their photoconductivity by combining three advanced transient spectroscopic methods including optical transient absorption (OTA), X-ray transient absorption (XTA), and optical pump terahertz probe (OPTP) spectroscopy. In addition to Cu-THQ, the CT in Cu/Zn-THQ after incorporating Zn 2+ guest metal nodes was also examined to uncover the contribution of through space pathway as the presence of the redox inactive 3d 10 Zn 2+ is expected to perturb the long range in-plane charge delocalization …”

“…In addition to Cu-THQ, the CT in Cu/Zn-THQ after incorporating Zn 2+ guest metal nodes was also examined to uncover the contribution of through space pathway as the presence of the redox inactive 3d 10 Zn 2+ is expected to perturb the long range in-plane charge delocalization. 29 Synthesis of M-THQ MOFs (M = Cu or Zn). Cu-THQ was synthesized according to previously published protocols.…”

X-ray snapshots reveal conformational influence on active site ligation during metalloprotein folding

“…24,25 The sample was excited with a 527 nm laser pulse at the Q-band of the heme in cyt c. 11 The 3 kHz, 527 nm laser pulse was generated the same way as reported in the previous publication done at the same beamline. 30 The sample was probed by monochromatic X-ray pulses (6.536 MHz, $80 ps fwhm) in a standard 24-bunch operating mode with $10 6 photons per pulse evenly separated by 153 ns. The excited volume exits the probing point as the sample jet ows.…”