Quantum-chemistry-aided ligand engineering for potential molecular switches: changing barriers to tune excited state lifetimes

Szemes, Dorottya Sárosiné; Keszthelyi, Tamás; Papp, Mariann; Varga, László; Vankó, György

doi:10.1039/d0cc04467a

Cited by 8 publications

(32 citation statements)

References 76 publications

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“…Our LVC model is based on DFT/TD-DFT employing the hybrid B3LYP* exchange–correlation functional , and the TZVP basis set for all atoms. The B3LYP* functional was chosen on the basis of its known accuracy for Fe complexes. − Two-electron integrals were approximated by the resolution of identity (RI-J) and chain of spheres (COSX) methods . For TD-DFT, we employ the Tamm–Dancoff approximation (TDA) .…”

Section: Methodsmentioning

confidence: 99%

Toward Simulation of Fe(II) Low-Spin → High-Spin Photoswitching by Synergistic Spin-Vibronic Dynamics

Pápai

2022

J. Chem. Theory Comput.

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A new theoretical approach is presented and applied for the simulation of Fe(II) low-spin (LS, singlet, t2g 6eg 0) → high-spin (HS, quintet, t2g 4eg 2) photoswitching dynamics of the octahedral model complex [Fe(NCH)6]2+. The utilized synergistic methodology heavily exploits the strengths of complementary electronic structure and spin-vibronic dynamics methods. Specifically, we perform 3D quantum dynamics (QD) and full-dimensional trajectory surface hopping (TSH, in conjunction with a linear vibronic coupling model), with the modes for QD selected by TSH. We follow a hybrid approach which is based on the application of time-dependent density functional theory (TD-DFT) excited-state potential energy surfaces (PESs) and multiconfigurational second-order perturbation theory (CASPT2) spin–orbit couplings (SOCs). Our method delivers accurate singlet–triplet–quintet intersystem crossing (ISC) dynamics, as assessed by comparison to our recent high-level ab initio simulations and related time-resolved experimental data. Furthermore, we investigate the capability of our simulations to identify the location of ISCs. Finally, we assess the approximation of constant SOCs (calculated at the Franck–Condon geometry), whose validity has central importance for the combination of TD-DFT PESs and CASPT2 SOCs. This efficient methodology will have a key role in simulating LS → HS dynamics for more complicated cases, involving higher density of states and varying electronic character, as well as the analysis of ultrafast experiments.

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Section: Methodsmentioning

confidence: 99%

Toward Simulation of Fe(II) Low-Spin → High-Spin Photoswitching by Synergistic Spin-Vibronic Dynamics

Pápai

2022

J. Chem. Theory Comput.

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“…The LVC potentials are based on B3LYP*/TZVP; the hybrid B3LYP* exchangecorrelation functional was selected for its known accuracy for excited-state energetics of Fe(II) complexes. 15,18,[30][31][32] Two-electron integrals were approximated by the resolution of identity (RI-J) 33 and chain-of-spheres (COSX) 34 methods. For TD-DFT caclulations, we used the Tamm-Dancoff approximation (TDA).…”

Section: Quantum Chemistrymentioning

confidence: 99%

“…Importantly, we herein achieve the so far highest complexity in terms of nuclear dimensionality and electronic states, including all the 3N − 6 nuclear coordinates as well as all accessible spin states in the simulation. We select the [Fe(terpy) 2 ] 2+ complex (Figure 1a, terpy = 2,2':6',2"-terpyridine), the principal molecule of our investigations across the years, [15][16][17][18] as a suitable representant of the Fe(II) polypyridines. Crucially, we present clear evidence that the sub-ps conversion to the quintet state occurs via the sequential pathway, with branching through the two 3 MC components, 3 T 1g and 3 T 2g (which differ in whether the 3d x 2 −y 2 or 3d z 2 e * g orbital is singly occupied); note that for simplicity, we use here octahedral notations.…”

Section: Introductionmentioning

confidence: 99%

Branching mechanism of photoswitching in Fe(II) polypyridyl complexes explained by full singlet-triplet-quintet dynamics

Rozgonyi

Vankó

Pápai

2022

Preprint

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It has long been known that irradiation with visible light converts Fe(II) polypyridines from their low-spin (singlet) to high-spin (quintet) state, yet mechanistic interpreation of the photorelaxation remains contraversal. Herein, we simulate the full singlet-triplet-quintet dynamics of the [Fe(terpy)2]2+ (terpy = 2,2’:6’,2’’-terpyridine) complex in full dimension, in order to clarify the complex photodynamics. Importantly, we report a branching mechanism with two sequential components: 3MLCT → 3MC(3T2g) → 5MC and 3MLCT → 3MC(3T2g) → 3MC(3T1g) → 5MC (MLCT = metal-to-ligand charge transfer, MC = metal-centered). While the direct 3MLCT → 5MC mechanism is considered as a relevant alternative, we show that it could only be operative and thus lead to competing pathways in the absence of 3MC states. The quintet state is populated on the sub-picosecond timescale involving non-exponential dynamics and coherent Fe-N breathing oscillations. The results are in agreement with the available time-resolved experimental data on Fe(II) polypiridines, and fully describe the photorelaxation dynamics.

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“…Having identified this as position 5 (β position with respect to Neq, the N atom of the side ring), we extended the study to single and double substitutions with Cl at the 5 and the 5" positions (on one or both of the side Py rings). Moreover, to confirm these substitution effects and examine their possible combination with the previously described axial (4') ED/EW tuning, 25 we have also included in this work the analogous derivatives of the [Fe(4'-SMe-terpy)2] 2+ complex. The effects of the substitutions are not only examined theoretically in this paper, but the latter compounds have also been synthesized, and their properties have been characterized experimentally.…”

Section: Introductionmentioning

confidence: 99%

“…7 kcal/mol) alteration of the quintet energy was achieved at the extremes, which resulted in a twentyfold difference in the quintet lifetime. 25 This defines the approximate range in which the properties are tunable with substitutions on the molecular axis of this complex.…”

Section: Introductionmentioning

confidence: 99%

Molecular engineering to tune functionality: the case of Cl substituted [Fe(terpy)2]2+

Papp

Keszthelyi

Vancza

et al. 2022

Preprint

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The properties of transition metal complexes and their chemical dynamics can be effectively modified with ligand substitutions, and theory can be a great aid to such molecular engineering. In this paper we first theoretically explore how substitution with a Cl atom at different positions of the terpyridine ligand affects the electronic structure of the [Fe(terpy)2]2+ complex. We found that besides the substitution at position 4’, the next most promising candidate to cause substantial electronic effects is that where the side pyridine ring is substituted at position 5 (beta). Therefore, next we examine in detail the Fe(II) complexes of the 5- chloro and 5,5”-di-chloro derivatives of terpy, theoretically and experimentally, to reveal how these substitutions modify the ground state properties and the lifetime of the excited quintet state in such complexes. In addition, we extend the investigation to the complexes of the analogously substituted derivatives of 4’-SMe-terpy. The substitution at position(s) 5 (and 5”) with Cl lowers the energy of the quintet state and increases its lifetime; the results on the 4’-SMe substituted complexes show similar changes with these two substitutions, verifying that these effects are more or less additive. This study contributes to the enhancement of our molecular engineering toolset for modifying the potential energy landscape of similar complexes.

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Quantum-chemistry-aided ligand engineering for potential molecular switches: changing barriers to tune excited state lifetimes

Abstract: DFT predicts the ability to tune the energy barrier between the quintet and singlet states of an iron complex, and thus the quintet lifetime, with selected substituents on the ligand; this prediction is confirmed by time-resolved spectroscopy.

Cited by 8 publications

References 76 publications

Toward Simulation of Fe(II) Low-Spin → High-Spin Photoswitching by Synergistic Spin-Vibronic Dynamics

Toward Simulation of Fe(II) Low-Spin → High-Spin Photoswitching by Synergistic Spin-Vibronic Dynamics

Branching mechanism of photoswitching in Fe(II) polypyridyl complexes explained by full singlet-triplet-quintet dynamics

Molecular engineering to tune functionality: the case of Cl substituted [Fe(terpy)2]2+

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