Provided herein are Ir(III) complexes comprising N-heterocyclic carbene ligand, method of synthesis of the Ir(III) complexes, a pharmaceutical composition comprises thereof. Also provided herein are the methods for the treatment and prevention of cancer/tumor in patients in need thereof by the administration of the Ir(III) complexes under both dark and light conditions. Also provided is a method of detecting the Ir(III) complex in a biological system. Also provided is a method of making the Ir(III) complex. The Ir(III) complexes possess anticancer activity such as the induction of cell death, inhibition of cellular proliferation, and inhibition of tumor growth in vivo.