Ultrafast excited state dynamics of NHC-Fe(II) complexes designed for light harvesting (Conference Presentation)

Haacke, Stefan; Liu, Li; Domenichini, Edoardo; Assfeld, Xavier; Monari, Antonio; Monerris, Antonio Frances; Beley, Marc; Avila, Cristina Cebrian; Magra, Kévin; Pastore, Mariachiara

doi:10.1117/12.2307244

Cited by 1 publication

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“…We can, however, safely exclude them to be singlet states since these would display stimulated emission, i.e., negative Δ A on the low-energy side of the GSB bands. Triplet states, as the 3 MLCT’s reported for complexes with tridentate ligands, do not show sizable stimulated emission since the radiative rate of the 3 MLCT-S 0 transition has a ∼3 orders of magnitude smaller radiative rate than the allowed singlet–singlet transitions . It is therefore most likely that the observed states X and Y are located on the triplet excited state PES presented in the computational studies.…”

Section: Resultsmentioning

confidence: 63%

“…Triplet states, as the 3 MLCT's reported for complexes with tridentate ligands, do not show sizable stimulated emission since the radiative rate of the 3 MLCT-S 0 transition has a ∼3 orders of magnitude smaller radiative rate than the allowed singlet−singlet transitions. 39 It is therefore most likely that the observed states X and Y are located on the triplet excited state PES presented in the computational studies. TAS could potentially differentiate the MC or MLCT character on the basis of the ESA spectra; however, a clear fingerprint differentiating one from the other has only been reported for the very specific case of [Fe(bpy)(CN) 4 ] 2− , where the 3 MLCT/MC crossover goes along with a strong solvatochromism.…”

Section: Inorganic Chemistrymentioning

confidence: 96%

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Impact of the fac/mer Isomerism on the Excited-State Dynamics of Pyridyl-carbene Fe(II) Complexes

et al. 2019

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The control of photophysical properties of iron complexes and especially of their excited states decay is a great challenge in the search for sustainable alternatives to noble metals in photochemical applications. Herein we report the synthesis and investigations of the photophysics of mer and fac iron complexes bearing bidentate pyridyl-NHC ligands, coordinating the Fe with three ligand-field enhancing carbene bonds. Ultrafast transient absorption spectroscopy reveals two distinct excited state populations for both mer and fac forms, ascribed to the populations of the T1 and the T2 states, respectively, which decay to the ground state via parallel pathways. We find 3-4 ps and 15-20 ps excited state lifetimes, with respective amplitudes depending on the isomer. The longer lifetime exceeds the one reported for iron complexes with tridentate ligands analogues involving four iron-carbene bonds. By combining experimental and computational results, a mechanism based on the differential trapping of the triplet states in spin-crossover regions is proposed for the first time to explain the impact of the fac/mer isomerism on the overall excited-state lifetimes. Our results clearly highlight the impact of bidentate Pyridyl-NHC ligands on the photophysics of iron complexes, especially the paramount role of fac/mer isomerism in modulating the overall decay process, which can be potentially exploited in the design of new Fe(II)-based photoactive compound.

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Section: Resultsmentioning

confidence: 63%

Section: Inorganic Chemistrymentioning

confidence: 96%