4-Hydroxy-3-iodobenzaldehyde is an aromatic aldehyde derivative featuring both a formyl group and a hydroxyl group on the benzene ring, with an iodine atom at the meta position relative to the hydroxyl group. This specific substitution pattern makes it a valuable bifunctional building block in organic synthesis. Its primary application is in the field of materials chemistry, particularly as a key intermediate for the synthesis of organic light-emitting diode (OLED) materials and other organic electronic compounds. The aldehyde group serves as a reactive handle for constructing conjugated molecular frameworks through condensation reactions (e.g., forming Schiff bases or via Suzuki coupling after conversion to a boronic ester), while the hydroxyl group can be further functionalized or participate in coordination. It is used in the development of novel electroluminescent and charge-transporting materials. As a versatile synthon, it also finds use in general organic synthesis for constructing more complex molecules, leveraging the reactivity of both the aldehyde and the halogen (iodine) for various cross-coupling and functional group transformation reactions.