In:
Chemical Science, Royal Society of Chemistry (RSC), Vol. 14, No. 37 ( 2023), p. 10129-10139
Abstract:
Iron N-heterocyclic carbene (FeNHC) complexes with long-lived charge transfer states are emerging as a promising class of photoactive materials. We have synthesized [Fe II (ImP) 2 ] (ImP = bis(2,6-bis(3-methylimidazol-2-ylidene-1-yl)phenylene)) that combines carbene ligands with cyclometalation for additionally improved ligand field strength. The 9 ps lifetime of its 3 MLCT (metal-to-ligand charge transfer) state however reveals no benefit from cyclometalation compared to Fe( ii ) complexes with NHC/pyridine or pure NHC ligand sets. In acetonitrile solution, the Fe( ii ) complex forms a photoproduct that features emission characteristics (450 nm, 5.1 ns) that were previously attributed to a higher ( 2 MLCT) state of its Fe( iii ) analogue [Fe III (ImP) 2 ] + , which led to a claim of dual (MLCT and LMCT) emission. Revisiting the photophysics of [Fe III (ImP) 2 ] + , we confirmed however that higher ( 2 MLCT) states of [Fe III (ImP) 2 ] + are short-lived ( 〈 10 ps) and therefore, in contrast to the previous interpretation, cannot give rise to emission on the nanosecond timescale. Accordingly, pristine [Fe III (ImP) 2 ] + prepared by us only shows red emission from its lower 2 LMCT state (740 nm, 240 ps). The long-lived, higher energy emission previously reported for [Fe III (ImP) 2 ] + is instead attributed to an impurity, most probably a photoproduct of the Fe( ii ) precursor. The previously reported emission quenching on the nanosecond time scale hence does not support any excited state reactivity of [Fe III (ImP) 2 ] + itself.
Type of Medium:
Online Resource
ISSN:
2041-6520
,
2041-6539
Language:
English
Publisher:
Royal Society of Chemistry (RSC)
Publication Date:
2023
detail.hit.zdb_id:
2559110-1
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