4-Mercaptophenylboronic acid is a bifunctional organic compound featuring both a boronic acid group and a thiol group. This unique structure makes it a versatile building block in materials science and synthetic chemistry. Its primary application is in the field of organic electronics and optoelectronics. The thiol group allows for strong covalent attachment to metal surfaces (e.g., gold, silver) via the formation of self-assembled monolayers (SAMs). The boronic acid group can then be used for further functionalization or to bind to specific analytes. This makes it a key precursor for modifying electrode surfaces in organic light-emitting diodes (OLEDs), organic photovoltaics (OPVs), and chemical sensors. It is used to create functional interfaces that improve charge injection, device stability, or sensing capabilities. As a synthetic intermediate, it serves as a valuable source of both boronic acid and thiol functionalities. It can participate in Suzuki-Miyaura cross-coupling reactions (via the boronic acid) and thiol-ene "click" chemistry or form disulfide bonds (via the thiol), enabling the construction of complex molecular architectures and functional materials.