Quantum Chemical Investigation on Phosphine‐Functionalized Charge‐Neutral Osmium(II) Complexes Bearing Bidentate/Tetradentate Pyridylpyrazolate‐Based Ligands

By altering the monodentate phosphine ligand (PR 3 ), a series of charge‐neutral Os II complexes 1a – 5a [Os(fppz) 2 (PR 3 ) 2 ] and 1b – 5b [Os(L‐NPh)(PR 3 ) 2 ] [fppz = 3‐(trifluoromethyl)‐5‐(2‐pyridyl)pyrazole; PR 3 = PMe 3 ( 1a / 1b ), PPhMe 2 ( 2a / 2b ), PPh 2 Me ( 3a / 3b ), PPh 3 ( 4a / 4b ), P(OPh) 3 ( 5a / 5b ); L‐NPh is two bis(pyridylpyrazolate] fragments connected by a phenylamino bridge at the 6‐position of the pyridyl rings] have been investigated by density functional theory (DFT) methods. The P(OPh) 3 substitution in 5a ( 5b ) rendered a considerable stabilization to the HOMO energy levels and an enlargement of the HOMO–LUMO energy gap compared with those of 1a – 4a ( 1b – 4b ), which led to a clear blueshift in the emission spectra. With the enhancement of the electron‐withdrawing strength of the phosphine ligands, the emissions are successively blueshifted from 1a / 1b to 4a / 4b . The results also revealed a general relationship between the variations of the emissions and changes to the Os–P bond lengths. The phenylamido bridge in 1b – 5b redshifted the absorption and emission spectra compared with those of 1a – 5a and decreased the Os(d) participation in the HOMOs, which led to dominant L‐ligand‐based 3 π–π* character for their emissive states compared with dominant metal‐to‐ligand charge‐transfer ( 3 MLCT) characters for 1a – 5a .