Butterfly-like photo-responsive cyclometalated Ir( <scp>iii</scp> ) complex: emergence of a future cancer therapeutic agent

Herein, we report photoinduced 2,2'-bipyrimidine-based mono- and binuclear cyclometalated iridium(III) complexes as a future promising anticancer agent, exhibiting the best efficiency as type I and type II PDT agents, respectively. The bimetallic complex LIr2 exhibits superior efficacy in normoxic (type II) and hypoxic (type I) tumour conditions, while the monometallic complex LIr is mainly active under normoxic conditions. This enhanced versatility makes LIr2 a highly promising candidate for photodynamic therapy. The complexes exhibited high serum albumin binding affinity (<i>K</i>_HSA = 0.57 × 10⁵ M^-1 for LIr and 0.59 × 10⁵ M^-1 for LIr2), highlighting their significant potential for biomolecular interactions. Under specific light irradiation, these complexes deplete glutathione levels, proving their efficacy as photodynamic therapeutic agents in future. Among the two synthesized complexes, LIr2 showed significant phototoxicity against the TNBC cell line (MDA-MB-231), exhibiting an IC₅₀ value of 13.6 ± 0.06 μM (PI = 9.9), highlighting its potential as an effective PDT agent.