Photophysical Evidence of Charge‐Transfer‐Complex Pairs in Mixed‐Linker 5‐Amino/5‐Nitroisophthalate CAU‐10

Abstract

The photochemistry of two isostructural metal-organic frameworks based on 5-amino/5-formamidoisophthalate (CAU-10-NH2 /NHCHO) or mixed-linker 5-amino/5-formamido- and 5-nitroisophthalate (CAU-10-NO2 /NH2 /NHCHO) has been studied using laser flash photolysis. 355 nm excitation of CAU-10-NH2 /NHCHO leads to a transient absorption spectrum characterized by a broad continuous absorption from 380 to 800 nm that was attributed to the presence of holes (440 nm) and electrons (600 nm) based on iPrOH and N2 O quenching, respectively. In contrast, no transients were observed for the isostructural mixed-linker CAU-10-NO2 /NH2 /NHCHO, data that is compatible with the uniform distribution of linkers 5-amino/5-formamido/5-nitroisophthalate as charge-transfer complex pairs. The same effect of quenching of 5-aminoisophthalate transients by 5-nitroisophthalate was also observed in aqueous solution (pH 9) but with much lower strength. Using a simple Stern-Volmer formalism allowed the estimation of the interaction of 5-aminoisophthalate with 5-nitroisophthalate in MOF to be 5.2×10(4) times stronger than in the aqueous phase.

Ruthenium(II) Tris(2,2′-bipyridyl) Complex Incorporated in UiO-67 as Photoredox Catalyst

“…Thus, the transient signals could not come from an irreversible reaction. These observations can be rationalized assuming that the intersystem crossing deactivation of the triplet excited state of Ru 2+ to the The photogeneration of long-lived charge separated states have been also previously observed for other related MOFs 6,10,18,[45][46][47]. However, unlike other related MOFs, this Rudcbpy-UiO-67(Zr) MOF is able to photogenerate an extremely long-lived charge separated state upon excitation with long wavelength visible light irradiation.…”

“…It can be seen in this Table 1 reported for other type of MOF materials. 6,10,18,45 The nature of the positive hole photogenerated after the PET process could be assigned, at first wavelength of its TAS depends on the chemical composition of the porous material in which it is photogenerated. [49][50][51] The TAS of the oxidized bpdc ligand, which is characterized by a continuous absorption in all the spectral range with higher absorption intensity at short wavelengths, is similar to the TAS recorded at long times, 500 µs, for the Rudcbpy-UiO-67(Zr)…”

“…These charge separated states can be characterized by their corresponding transient absorption spectra. 6,10,18 The development of photoresponsive MOFs is a topic of large interest that can serve to obtain highly active photocatalyst for pollutant degradation [19][20] and solar fuel productions among other applications. [21][22][23][24] It would be important to go beyond these two areas to develop also photocatalysts for general organic transformation.…”

Guest–Host Complexes of TCNQ and TCNE with Cu3(1,3,5-benzenetricarboxylate)2

“…Host–guest interactions can also promote charge transfer (CT) between the host framework and interstitial guest molecules. This process occurs via molecular orbital hybridization between the guest molecules and the framework to produce partial charge delocalization between the components, resulting in a charge transfer system. , For an electroactive framework, treatment with oxidizing or reducing agents can induce redox processes that result in the concomitant introduction or expulsion of counterion guests. − One of the possible applications of this effect is in molecular sensing, since the formation of CT systems would modify properties of the framework such as luminescence , as well as enhancing conductivity due to the generation of charge carriers. ,, …”

Photoinduced electron transfer in porous organic salt crystals impregnated with fullerenes

“…1 There are many examples of MOFs in which energy and electron transfer has been investigated by fixing the distance and orientation between chromophores, which were precisely determined by single crystal X-ray crystallography. [2][3][4][5][6][7][8][9][10] As compared with MOFs, porous organic salts (POSs) have advantage in terms of synthetic versatility, easier processing, more flexibility and better workability. [11][12][13][14][15] In particular, POSs composed of ammonium cations and sulfonate anions have enabled various systematic designs of the resultant porous structures by changing the combination of ionic components using strong intermolecular interactions such as hydrogen bonds and electrostatic interactions.…”