Biporous Cd(II) Coordination Polymer via in Situ Disulfide Bond Formation: Self-Healing and Application to Photosensitive Optoelectronic Device

A heteroporous metal-organic framework, [Cd₂(2,2'-DSB)₂(INH)₂(H₂O)₂]_n (1), is fabricated by the reaction of CdI₂, 2-mercaptobenzoic acid (2-MBAH), and isoniazid (INH). The X-ray structure of the compound 1 shows the bridging INH and 2,2'-disulfanediyldibenzoic acid (H₂2,2'-DSBA) around the Cd(II) ion center. 2-MBAH has been in situ dimerized to the formation of 2,2'-DSB^2- (S-S-bonded dianion), which has further extended to form the 2D network. However, supramolecular assembly via π···π and hydrogen bonds strengthens the structural motif within the 3D array. Optical stimulation generated the thiol radical under an argon environment followed by the electron paramagnetic resonance (EPR) study, but upon exposure to air, the EPR signal gradually disappeared by the formation of the S-S bond, which was commonly known as a self-healing property. Again, compound 1 exhibited as a semiconducting material with a band gap of 3.7 eV. The I-V characteristics of 1 show that the conductivity is intensified by an optical response. The Schottky diode property of 1 shows a lower barrier height, a lower resistance, and a higher conductivity upon illumination at 360 nm.