Fe(III) complexes with prolonged luminescence lifetimes and symmetry-breaking charge separation

Abstract Iron(III) complexes with long-lived luminescence in fluid solution at room temperature (up to 6.5 ns, significantly longer than benchmark compounds) have been prepared, by taking advantage of the excited-state equilibration approach, for the first time applied to earth-abundant, iron(III) compounds. Pyrene subunits have been covalently-linked by methylene linkage to [Fe(phtmeimb)2]+ (1; phtmeimb is {phenyl[tris(3-methylimidazol-1-ylidene)]borate}−), so obtaining complex 3, and have been used to synthesize [Fe(pytmeimb)2]+ (2; pytmeimb is {2-pyrene[tris(3-methylimidazol-1-ylidene)]borate}−). In 2 and 3, the ligand-to-metal charge transfer (2LMCT) state decays by energy transfer to closely-lying p-p* pyrene triplets. Equilibrated states are so formed, resulting in 2LMCT emission from the Fe(III) subunit, in which pyrene triplets serve as long-lived excited-state reservoirs. In 2, symmetry-breaking charge separation in dilute fluid solution at room temperature also occurs.