Unusually Large Singlet Oxygen ( 1 O 2 ) Production by Very Weakly Emissive Pyrene‐Functionalized Iridium(III) Complex: Interplay between Excited 3 ILCT/ 3 IL and 3 MLCT States

The photophysical properties of a few Ir(III) and Rh(III) complexes have been attempted to be correlated ( 1–4 ) with their 1 O 2 generation efficiencies. A very weakly emissive pyrene‐functionalized Ir(III) complex ( 1 ) produces 1 O 2 more efficiently than the other more emissive Ir(III) complexes. All of them have excited triplet state lifetimes (τ T ) in the microsecond regime. However, the pyrene‐functionalized Ir(III) complex possesses the largest τ T and has reasonable HOMO (highest occupied molecular orbital) energy (< –5.51 eV) which is desired for efficient 1 O 2 production. 1–4 emit mostly from the 3 MLCT state. The lowest triplet emissive state of 3 and 4 is the 3 MLCT state while it is the 3 ILCT/ 3 IL state for 1 which is mostly non‐emissive. However, the large excited state lifetime and the small energy gap between the 3 ILCT/ 3 IL states and the ground electronic state for complex 1 facilitates efficient energy transfer to molecular 3 O 2 producing 1 O 2 .