![]() ![]() Rigid anionic tripodal carbenes achieve a 2LMCT lifetime of 2 ns, with a quantum yield of 2% in aerated MeCN solution 16. 15 exhibits fluorescence from a 2LMCT state with a lifetime of ~100 ps. The Fe III congener of the Fe II complex with an MLCT lifetime of 0.5 ns presented by Wärnmark et al. Only recently, one emissive mononuclear Fe II complex was reported 13, 14, while two emissive Fe III complexes possessing six electron-donating carbene donor units have been reported so far 15, 16. Exceptionally long MLCT lifetimes could be obtained: (1) with six N-heterocyclic carbene (NHC) donor groups ( τ = 0.5 ns) 10 and (2) using the HOMO inversion concept 11 ( τ = 2.7 ns) 12. In Fe II complexes, these strategies typically lead to MLCT lifetimes in the picosecond range. Attempts to invert the order of metal-centred and charge-transfer states focus on the destabilization of metal-centred levels by strong σ donors 3, 4, 5 or the stabilization of charge-transfer states by π acceptors 6, 7, 8, 9. Consequently, short lifetimes are observed for charge-transfer states 2. The low-energy metal-centred states act as dark excited-state traps, quenching potentially emissive metal-to-ligand charge-transfer (MLCT) or ligand-to-metal charge-transfer (LMCT) states. The greatest challenge in the search for photoactive iron complexes is posed by the weak ligand field splitting of t 2g- and e g*-based orbitals, which is smaller in 3 d transition metal complexes compared with their 4 d and 5 d counterparts 1. With a lifetime of 4.6 ns, the strongly reducing and oxidizing MLCT-dominated state can initiate electron transfer reactions, which could constitute a basis for future applications of iron in photoredox catalysis. The low-lying π* levels of the cyclometalating units lead to energetically accessible MLCT states that cannot evolve into LMCT states. This behaviour is achieved by a ligand design that combines four N-heterocyclic carbenes with two cyclometalating aryl units. Here we report the Fe III complex (HImP = 1,1′-(1,3-phenylene)bis(3-methyl-1-imidazol-2-ylidene)), showing a Janus-type dual emission from ligand-to-metal charge transfer (LMCT)- and metal-to-ligand charge transfer (MLCT)-dominated states. ![]() ![]() Emissive iron compounds are scarce and dual emission has not been observed before. the ions formed are negative, because they have more electrons than protonsįor elements in groups 6 and 7, the charge on the ion is equal to (8 minus group number).Although iron is a dream candidate to substitute noble metals in photoactive complexes, realization of emissive and photoactive iron compounds is demanding due to the fast deactivation of their charge-transfer states.The outer shells of non-metal atoms gain electrons when they form ions: A sodium atom loses one electron to form a sodium ion Forming negative ions the ions have the electronic structure of a noble gas (group 0 element), with a full outer shellįor elements in groups 1, 2 and 3, the number of electrons lost is the same as the group number.the ions are positive, because they have more protons than electrons.Metal atoms lose electrons from their outer shell when they form ions: non-metal atoms gain electrons to form negatively charged ions.metal atoms lose electrons to form positively charged ions.Ions form when atoms lose or gain electrons to obtain a full outer shell: An ion is an atom or group of atoms with a positive or negative charge.
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