The reaction of zirconium salts with meso-tetra(4carboxyphenyl)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 Xray diffraction and scanning electron microscopy, modulator candidates and the optimal synthetic conditions yielding phase-pure PCN-222, PCN-223, and MOF-525 were identified. 1 H nuclear magnetic resonance analysis, thermogravimetric analysis, and N 2 gas sorption measurements were performed on select MOFs to gain insight into the relationship between their defectivity and modulator properties.

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).

We present a detailed investigation of the photophysical properties of mixed-ligand pyrene-and porphyrin-based metal−organic frameworks (MOFs) as a function of their 3D structure. Solvothermal reactions between metal salts (InCl 3 , Zr(acac) 4 , and ZrCl 4 ) and suitable ratios of 1,3,6,8-tetrakis(p-benzoic acid)pyrene (TBAPy) and meso-tetrakis-(4-carboxyphenyl)porphyrin (TCPP) were performed to prepare a series of mixed-ligand ROD-7, NU-901, and NU-1000 MOFs. Time-resolved and steady-state fluorescence measurements were conducted on the mixed-ligand MOFs to study their photophysics. Based on the results, we concluded that upon excitation of TBAPy linkers in the MOFs, singlet excitation energy migrates across TBAPy linkers until it finds a TCPP unit. TCPP acts as an energy trap and quenches the excitation. The efficiency of TBAPy-to-TBAPy energy transfer was found to be sensitive to the structural parameters of MOFs. Analysis of steady-state and time-resolved fluorescence data revealed that excitation energy transfer (EET) is most efficient in ROD-7, followed by NU-901 and NU-1000. We propose that topology that invokes the shorter interchromophoric distances between TBAPy linkers in ROD-7 is responsible for its higher EET efficiency. The distance dependence of the EET rate constant (k EET ) was investigated to gain insight into the mechanistic aspects of energy transfer in MOFs. This study revealed that (a) energy transfer in MOFs deviates from the classical Forster model and (b) the geometrical arrangement of linkers influences the mechanism of EET in MOFs. A theoretical investigation was also performed to determine energy-transfer rate constants along different directions and assess the directionality of energy transfer in these MOFs. The magnitude of rate constants indicated that energy transfer in ROD-7 should be highly anisotropic along the stacking direction. These findings suggest that ROD-7 is a promising candidate to play the role of the light-harvesting and energy-transfer component in solar energy conversion devices, where directional energy transfer is required.

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