The effect of N-heterocyclic carbene units on the absorption spectra of Fe(ii) complexes: a challenge for theory

Abstract

The absorption spectra of five Fe(ii) homoleptic and heteroleptic complexes containing strong sigma-donating N-heterocyclic carbene (NHC) and polypyridyl ligands have been theoretically characterized using a tuned range-separation functional.

Distinct photodynamics of κ-N and κ-C pseudoisomeric iron(ii) complexes

“…The origin of this problem is currently not clear. 20 For both complexes, the lowest adiabatic triplet state has MC character with energies of 1.31 eV (946 nm) for Fe1 and 1.62 eV (765 nm) for Fe2. Both energies are sufficient for effective oxygen quenching.…”

“…1. 7,[19][20][21] The intense bands below 350 nm are dominated by ligand p-p* transitions. The presence of small intensity MLCT transitions in this region should be noted.…”

Bidentate Pyridyl‐NHC Ligands: Synthesis, Ground and Excited State Properties of Their Iron(II) Complexes and the Role of the fac/mer Isomerism

“…In this context, insights provided by molecular modeling and simulations have all their attractiveness and importance. Traditionally, computational methods have been used to predict structures, describe spin-crossover phenomena, [77][78][79] predict electrochemical properties, [80,81] rationalize optical properties, [60,[82][83][84][85][86] and elucidate the nature and relative alignment of MLCT and MC states and the barriers for their mutual interconversion. [87,88] The large size of the iron-organic complexes often imposes the use of DFT and TD-DFT as methods of choice for tackling this problem, although the development and use of other methodologies derived from multiconfigurational approaches (sometimes in combination with DFT, as in hybrid DFT/wavefunction formalisms) is growing in the last years.…”

Excitation Energy-Dependent Branching Dynamics Determines Photostability of Iron(II)–Mesoionic Carbene Complexes

“…Gros et al explored diazine systems to modulate the electron density on the central nitrogen for increased MLCT lifetime . Heteroleptic complexes utilizing the broad absorption of tpy systems and the σ-donating properties of NHC ligands were reported. − Introducing cyclometalated bonds also stabilizes the MLCT states and can hinder population of the 5 MC state . Recently, a Fe­(II) complex featuring only N-bound iron but nanosecond CT excited-state lifetimes was reported by raising the highest occupied molecular orbital energies and utilizing strong electron acceptors .…”