Light harvesting and energy transfer in a porphyrin-based metal organic framework.

We present the synthesis and photophysical characterization of a water stable PCN-223(freebase) metal organic framework (MOF) constructed from meso-tetrakis(4-carboxyphenyl)porphyrin (TCPP). The photophysical properties of the synthesized crystalline material were studied using a wide range of steady-state and time-resolved spectroscopic techniques. Quenching experiments performed on TCPP and PCN-223 demonstrated that the extent and the rate of quenching in the MOF is significantly higher than the monomeric ligand. Based on these results, we propose that upon photo-excitation, the singlet excitation energy migrates across neutral TCPP linkers until it is quenched by a N-protonated TCPP linker. The N-protonated linkers act as trap states that deactivate the excited state to the ground state. Variable temperature measurements aided in understanding the mechanism of singlet-singlet energy transfer in the PCN-223 MOF. The rate of energy transfer and the total exciton hopping distance in PCN-223 were calculated in order to quantify the energy transfer characteristics of PCN-223. Nanosecond transient absorption spectroscopy was used to study the triplet excited state photophysics in both the free ligand and PCN-223 MOF. Furthermore, femtosecond transient absorption spectroscopy was employed to get a better understanding of the photophysical processes taking place in the ligand and MOF on ultrafast timescales. Efficient energy transfer (Förster radius = 54.5 Å) accompanied with long distance exciton hopping (173 Å) was obtained for the PCN-223 MOF.

Synthesis and Defect Characterization of Phase-Pure Zr-MOFs Based on Meso-tetracarboxyphenylporphyrin.

The reaction of zirconium salts with meso-tetra(4-carboxyphenyl)porphyrin (TCPP) in the presence of different modulators results in the formation of a diverse set of metal-organic frameworks (MOFs), each displaying distinct crystalline topologies. However, the synthesis of phase-pure crystalline frameworks remains challenging due to the concurrent formation of different polymorphs. The acidity and concentration of the modulator greatly influence the outcome of the MOF synthesis. By systematically varying these two parameters, selective framework formation can be achieved. In the present study, we aimed to elucidate the effect of modulator on the synthesis of zirconium-based TCPP MOFs. With the help of powder X-ray diffraction and scanning electron microscopy, modulator candidates and the optimal synthetic conditions yielding phase-pure PCN-222, PCN-223, and MOF-525 were identified. 1H nuclear magnetic resonance analysis, thermogravimetric analysis, and N2 gas sorption measurements were performed on select MOFs to gain insight into the relationship between their defectivity and modulator properties.

Immunocompromised children and young people are at no increased risk of severe COVID-19.

OBJECTIVES: We aimed to prospectively describe the incidence and clinical spectrum of SARS-CoV-2 infection in immunocompromised paediatric patients in the UK. METHODS: From March 2020 to 2021 weekly questionnaires were sent to immunocompromised paediatric patients or their parents. Information, including symptom presentation and SARS-CoV-2 PCR test results, was collected from 1527 participants from 46 hospitals. Cross-sectional serology was investigated in February and March 2021. RESULTS: Until the end of September 2020, no cases were reported. From September 28th 2020 to March 2021 a total of 38 PCR-detected SARS-CoV-2 infections were reported. Of these, four children were admitted to hospital but none had acute severe COVID-19. Increasing age in association with immunodeficiency increased reporting of SARS-CoV-2 infection. Worsening of fever, cough, and sore throat were associated with participants reporting SARS-CoV-2 infection. Serology data included 452 unvaccinated participants. In those reporting prior positive SARS-CoV-2 PCR, there were detectable antibodies in 9 of 18 (50%). In those with no prior report of infection, antibodies were detected in 32 of 434 (7•4%). CONCLUSIONS: This study shows SARS-CoV-2 infections have occurred in immunocompromised children and young people with no increased risk of severe disease. No children died.