The photo-switching study of guest 2-(phenylazo)pyridine (PAP) embedded in solid host material MOF-5

Abstract

Herein, a photo-responsive molecule, 2-phenylazopyridine (PAP) was incorporated as a guest into a porous crystalline metal-organic framework (MOF), MOF-5. Detail experimental studies like elemental analysis, PXRD measurements, IR spectroscopy have been performed to confirm the successful embedment of PAP into the host framework. Thermogravimetric and elemental analysis revealed that two PAP molecules per unit of the host were present in the host-guest composite, MOF-5⊃PAP. Photo-switching study of the composite MOF-5⊃PAP was performed and investigated by details IR spectroscopy and UV-Vis spectroscopy. The percentage of photo-induced trans to cis isomerization of the guest molecule, PAP in the hybrid host-guest compound (MOF-5⊃PAP) was less compared to the azobenzene embedded in MOF-5 i.e. AZB@MOF-5. There is no structural transformation of the host MOF-5 after loading PAP or prolong UV irradiation, exhibiting the non-responsive nature of the framework retaining its cubic lattice structure. This was also reflected in N2 adsorption isotherm as no change in the isotherm was observed even after prolong photo-irradiation in the hybrid MOF-5⊃PAP composite.