Unusually Large Singlet Oxygen (1O2) Production by Very Weakly Emissive Pyrene-Functionalized Iridium(III) Complex: Interplay between Excited 3ILCT/3IL and 3MLCT States

Article abstract of DOI:10.1002/ejic.202000442

The photophysical properties of a few Ir(III) and Rh(III) complexes have been attempted to be correlated (1–4) with their ¹O₂ generation efficiencies. A very weakly emissive pyrene-functionalized Ir(III) complex (1) produces ¹O₂ 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 ¹O₂ production. 1–4 emit mostly from the ³MLCT state. The lowest triplet emissive state of 3 and 4 is the ³MLCT state while it is the ³ILCT/³IL state for 1 which is mostly non-emissive. However, the large excited state lifetime and the small energy gap between the ³ILCT/³IL states and the ground electronic state for complex 1 facilitates efficient energy transfer to molecular ³O₂ producing ¹O₂.