Photochemical Response of Commercial MOFs: Al₂(BDC)₃ and Its Use As Active Material in Photovoltaic Devices

Abstract

The presence of organic linkers in MOFs allows introducing response in the solid upon chemical, electrochemical, or photochemical excitation of these units. In the present study, we report the intrinsic photoresponse of four commercially available MOFs as well as after incorporation of some organic guests. Laser flash photolysis measurements have allowed us to detect transient species upon irradiation of commercial Al2(BDC)3. The signal has been rationalized as derived from the photochemical generation of charge separated states. In contrast to Al2(BDC)3, the other three commercial MOFs tested did not exhibit any signal. The photoinduced charge separation in Al2(BDC)3 can be modulated by inclusion of organic guests that can act as traps of electrons or holes increasing the lifetime of charge separation. When the oxidation potential of the organic guest is low, as in the case of 1,4-phenylendiamine, PDA, we have been able to observe spontaneous charge separation even for Fe-BTC and Cu3(BTC)2. The basic understanding of the photoresponse has been applied to build photovoltaic cells using Al2(BDC)3 as semiconductor. The best performing device was the one constructed with 1,4-dimethoxybenzene, DMB, DMB@ Al2(BDC)3 with the lowest thickness, which more than doubles the efficiency of the Al2(BDC)3 cells prepared without DMB. Overall, our report exemplifies how understanding of the basic photochemistry can be used for developing new applications of MOFs.

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

“…There are previous studies in the literature [15,16,19,24] where Zn 2 + , Ti 8 O 8 , and Al 3 + MOFs have been subjected to laser flash photolysis and generation of sub-millisecond transients was observed. These were attributed also to the occurrence of photo-induced electron transfer from electron-rich ligands to the metal clusters leading to a state of charge separation.…”

“…Soon after Zecchina's group reported the photoluminescence of MOF-5, [14] we reported the first example showing that MOF-5 can behave as a photocatalyst. [15][16][17] Photoactivity of MOFs opens the way for their application as photocatalysts for the degradation of pollutants [15] and for hydrogen generation from water/methanol mixtures, [18] as well as their use as sensors and in optoelectronic devices. [15][16][17] Photoactivity of MOFs opens the way for their application as photocatalysts for the degradation of pollutants [15] and for hydrogen generation from water/methanol mixtures, [18] as well as their use as sensors and in optoelectronic devices.…”

Three coordination compounds of cobalt with organic carboxylic acids and 1,10-phenanthroline as ligands: syntheses, structures and photocatalytic properties

“…Under UV light irradiation, some electrons will be transferred from the HOMO to the LUMO [1,[30][31][32][33]. The HOMO is derived mainly from O and/or N 2p bonding orbitals, while the LUMO is mainly constructed from empty metal orbitals.…”

Four coordination compounds constructed from 1,10-phenanthroline and semi-flexible and flexible carboxylic acids: Hydrothermal synthesis, optical properties and photocatalytic performance

“…In the presence of UV light, there is an electron transfer from the highest occupied molecular orbital (HOMO) to the lowest unoccupied molecular orbital (LUMO) [16,[45][46][47]. The HOMO is mainly contributed by O and/or N 2p bonding orbitals, and the LUMO is mainly contributed by empty M (like Mn) orbitals.…”