Tuning Structural and Optical Properties of Porphyrin‐based Hydrogen‐Bonded Organic Frameworks by Metal Insertion

Abstract

Herein, a simple way of tuning the optical and structural properties of porphyrin‐based hydrogen‐bonded organic frameworks (HOFs) is reported. By inserting transition metal ions into the porphyrin cores of GTUB‐5 (p‐H8‐TPPA (5,10,15,20‐Tetrakis[p‐phenylphosphonic acid] HOF), the authors show that it is possible to generate HOFs with different band gaps, photoluminescence (PL) life times, and textural properties. The band gaps of the resulting HOFs (viz., Cu‐, Ni‐, Pd‐, and Zn‐GTUB‐5) are measured by diffuse reflectance and PL spectroscopy, as well as calculated via DFT, and the PL lifetimes are measured. Across the series, the band gaps vary over a narrow range from 1.37 to 1.62 eV, while the PL lifetimes vary over a wide range from 2.3 to 83 ns. These differences ultimately arise from metal‐induced structural changes, viz., changes in the metal‐to‐nitrogen distances, number of hydrogen bonds, and pore volumes. DFT reveals that the band gaps of Cu‐, Zn‐, and Pd‐ GTUB‐5 are governed by highest occupied/lowest unoccupied crystal orbitals (HOCO/LUCO) composed of π‐ orbitals on the porphyrin linkers, while that of Ni‐GTUB‐5 is governed by a HOCO and LUCO composed of Ni dorbitals. Overall, our findings show that metal‐insertion can be used to optimize HOFs for optoelectronics and small‐molecule capture applications.

Creating Order in Ultrastable Phosphonate Metal–Organic Frameworks via Isolable Hydrogen-Bonded Intermediates

“…A key point is the HMOF intermediate. Phosphonate linkers have been studied for the formation of hydrogen-bonded organic frameworks (HOFs) owing to their ability to form multiple charge-assisted H-bonds . As any precipitated solid in an HOF synthesis may not necessarily represent the desired HOF, rapidly precipitated solids from this HMOF approach can be phases other than the target.…”

“…We sought to utilize these hydrogen-bonded metal–organic frameworks (HMOFs) as intermediates to synthesize highly robust chromium­(III)–phosphonate MOFs by dehydrating the [Cr­(H 2 O) 6 ] 3+ ions to induce direct metal phosphonate coordination. Phosphonate linkers have been employed to form hydrogen-bonded structures both with metal ions and without, but the resultant structures do not carry the hallmark phosphonate stability. As a hypothesis, the order observed in the HMOF could be translated to the MOF as a method of overcoming the crystallization challenges associated with metal phosphonate materials.…”

Nonlinear optical properties of porphyrin-based covalent organic frameworks determined by steric-orientation of conjugation

“…The addition of central coordination metal Co enhanced the RSA intensity, which can be attributed to the extended conjugation within the porphyrin unit and the efficient charge transport process. 50,51 The input-output energy density curves calculated from the corresponding Z-scan curves are shown in Fig. 4f, which reflects a typical OL behavior.…”

Ultra-High Proton Conductivity iHOF Based on Guanidinium Arylphosphonate for Proton Exchange Membrane Fuel Cells

“…It facilitates the formation of structurally diverse frameworks. 49,50 Although most of the research on hydrogen bonding by phosphoric acid groups are single-component systems, 51,52 its contribution to proton conduction is enormous. The porous HOFs (UPC-H5) are constructed based on phosphonate-based porphyrin nickel building block, and the proton conductivity of UPC-H5a@ NH 3 •H 2 O can be increased by 2 orders of magnitude up to 1.59 × 10 −1 S•cm −1 by the guest conditioning strategy.…”

“…Compared with sulfonates, polyacid phosphonates can realize nondeprotonation, semideprotonation, and full deprotonation, which are conducive to the formation of more abundant hydrogen bonding patterns and different types of hydrogen bonds. It facilitates the formation of structurally diverse frameworks. , Although most of the research on hydrogen bonding by phosphoric acid groups are single-component systems, , its contribution to proton conduction is enormous. The porous HOFs (UPC-H5) are constructed based on phosphonate-based porphyrin nickel building block, and the proton conductivity of UPC-H5a@NH 3 ·H 2 O can be increased by 2 orders of magnitude up to 1.59 × 10 –1 S·cm –1 by the guest conditioning strategy .…”