Strongly Phosphorescent Neutral Rhenium(I) Isocyanoborato Complexes: Synthesis, Characterization, and Photophysical, Electrochemical, and Computational Studies

A new series of neutral isocyanoborato rhenium(I) diimine complexes [Re(CO)(3)(N<^>N)(CNBR3)], where N<^>N=bpy, 4,4-Me(2)bpy, phen, 4,7-Me(2)phen, 2,9-Me(2)phen, 3,4,7,8-Me(4)phen; R=C6F5, C6H5, Cl, 4-ClC6H4, 3,5-(CF3)(2)C6H3, with various isocyanoborate and diimine ligands of diverse electronic and steric nature have been synthesized and characterized. The X-ray crystal structures of six complexes have also been determined. These complexes displayed intense bluish green to yellow phosphorescence at room temperature in dichloromethane solution. The photophysical and electrochemical properties of these complexes had been investigated. To elucidate the electronic structures and transitions of these complexes, DFT and TD-DFT calculations have been performed, which revealed that the lowest-energy electronic transition associated with these complexes originates from a mixture of MLCT [d(Re)*(N<^>N)] and LLCT [(CNBR3)*(N<^>N)] transitions.