A series of luminescent iridium(III) complexes were synthesized and evaluated for their ability to interact with hydroxide ions in semi-aqueous media at ambient temperature. Upon the addition of OH⁻, a nucleophilic aromatic substitution reaction takes place at the bromine groups of the N^N ligand of complex 1, resulting in the generation of a yellow-green luminescence. Complex 1 showed a 35-fold enhanced emission at pH 14 when compared to neutral pH, and the detection limit for OH⁻ ions was 4.96 μM. Complex 1 exhibited high sensitivity and selectivity, long-lived luminescence and impressive stability. Additionally, we have demonstrated the practical application of complex 1 to detect OH⁻ ions in simulated wastewater.