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

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 ( 2 LMCT) state decays by energy transfer to closely-lying p-p* pyrene triplets. Equilibrated states are so formed, resulting in 2 LMCT 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.