Heteroleptic iridium(iii) complexes bearing a coumarin moiety: an experimental and theoretical investigation

Orange coloured complexes with the general formula [Ir(2-pypy)₂(L)] have been synthesized in excellent yields by reacting [Ir(2-pypy)₂(Cl)]₂ with HL in a ratio of 1 : 1 in a 1 : 1 mixture of ethanol and dichloromethane in an argon atmosphere. Herein, L^- is the deprotonated aldimine form of 7-hydroxy-4-methyl-2-oxo-2H-chromene-8-carbaldehyde and 1-napthylamine (HL¹), 2-aminoanthracene (HL²) and 2-aminofluorene (HL³), respectively. The elemental analysis and ESI mass spectroscopic measurements ensured the formation of the desired complexes. The molecular structure of [Ir(2-pypy)₂(L¹)] was confirmed by single-crystal X-ray diffraction. The complexes were also characterized by different spectroscopic techniques. The ground and excited-state geometries, NMR, absorption, and phosphorescence properties of the three Ir(iii) complexes were examined by DFT and TDDFT methods. The natural transition orbital (NTO) and spin density difference map analysis reveals the nature of excitations. The lowest lying triplet excited state is associated with the ³IL and ³ML excited state. The emission-like transition is consistent with the strong ³ILCT and ³MLCT character.