| 1. |
- Rein, Christian, et al.
(författare)
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Element-specific investigations of ultrafast dynamics in photoexcited Cu2ZnSnS4 nanoparticles in solution
- 2021
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Ingår i: Structural Dynamics. - : AIP Publishing. - 2329-7778. ; 8:2
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Tidskriftsartikel (refereegranskat)abstract
- Ultrafast, light-induced dynamics in copper-zinc-tin-sulfide (CZTS) photovoltaic nanoparticles are investigated through a combination of optical and x-ray transient absorption spectroscopy. Laser-pump, x-ray-probe spectroscopy on a colloidal CZTS nanoparticle ink yields element-specificity, which reveals a rapid photo-induced shift of electron density away from Cu-sites, affecting the molecular orbital occupation and structure of CZTS. We observe the formation of a stable charge-separated and thermally excited structure, which persists for nanoseconds and involves an increased charge density at the Zn sites. Combined with density functional theory calculations, the results provide new insight into the structural and electronic dynamics of CZTS absorbers for solar cells.
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| 2. |
- Biasin, Elisa, et al.
(författare)
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Femtosecond X-Ray Scattering Study of Ultrafast Photoinduced Structural Dynamics in Solvated[Co(terpy)2]2$
- 2016
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Ingår i: Physical Review Letters. - : American Physical Society (APS). - 1079-7114 .- 0031-9007. ; 117:1
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Tidskriftsartikel (refereegranskat)abstract
- We study the structural dynamics of photoexcited [Co(terpy)2]2+ in an aqueous solution with ultrafast x-ray diffuse scattering experiments conducted at the Linac Coherent Light Source. Through direct comparisons with density functional theory calculations, our analysis shows that the photoexcitation event leads to elongation of the Co-N bonds, followed by coherent Co-N bond length oscillations arising from the impulsive excitation of a vibrational mode dominated by the symmetrical stretch of all six Co-N bonds. This mode has a period of 0.33 ps and decays on a subpicosecond time scale. We find that the equilibrium bond-elongated structure of the high spin state is established on a single-picosecond time scale and that this state has a lifetime of ∼7 ps.
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| 3. |
- Canton, Sophie, et al.
(författare)
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Toward Highlighting the Ultrafast Electron Transfer Dynamics at the Optically Dark Sites of Photocatalysts
- 2013
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Ingår i: The Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 4:11, s. 1972-1976
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Tidskriftsartikel (refereegranskat)abstract
- Building a detailed understanding of the structure function relationship is a crucial step in the optimization of molecular photocatalysts employed in water splitting schemes. The optically dark nature of their active sites usually prevents a complete mapping of the photoinduced dynamics. In this work, transient X-ray absorption spectroscopy highlights the electronic and geometric changes that affect such a center in a bimetallic model complex. Upon selective excitation of the ruthenium chromophore, the cobalt moiety is reduced through intramolecular electron transfer and undergoes a spin flip accompanied by an average bond elongation of 0.20 +/- 0.03 angstrom. The analysis is supported by simulations based on density functional theory structures (B3LYP*/TZVP) and FEFF 9.0 multiple scattering calculations. More generally, these results exemplify the large potential of the technique for tracking elusive intermediates that impart unique functionalities in photochemical devices.
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| 4. |
- Canton, Sophie, et al.
(författare)
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Visualizing the non-equilibrium dynamics of photoinduced intramolecular electron transfer with femtosecond X-ray pulses.
- 2015
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 6
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Tidskriftsartikel (refereegranskat)abstract
- Ultrafast photoinduced electron transfer preceding energy equilibration still poses many experimental and conceptual challenges to the optimization of photoconversion since an atomic-scale description has so far been beyond reach. Here we combine femtosecond transient optical absorption spectroscopy with ultrafast X-ray emission spectroscopy and diffuse X-ray scattering at the SACLA facility to track the non-equilibrated electronic and structural dynamics within a bimetallic donor-acceptor complex that contains an optically dark centre. Exploiting the 100-fold increase in temporal resolution as compared with storage ring facilities, these measurements constitute the first X-ray-based visualization of a non-equilibrated intramolecular electron transfer process over large interatomic distances. Experimental and theoretical results establish that mediation through electronically excited molecular states is a key mechanistic feature. The present study demonstrates the extensive potential of femtosecond X-ray techniques as diagnostics of non-adiabatic electron transfer processes in synthetic and biological systems, and some directions for future studies, are outlined.
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| 5. |
- Chábera, Pavel, et al.
(författare)
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A low-spin Fe(iii) complex with 100-ps ligand-to-metal charge transfer photoluminescence
- 2017
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 543:7647, s. 695-699
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Tidskriftsartikel (refereegranskat)abstract
- Transition-metal complexes are used as photosensitizers1, in light-emitting diodes, for biosensing and in photocatalysis2. A key feature in these applications is excitation from the ground state to a charge-transfer state3,4; the long charge-transfer-state lifetimes typical for complexes of ruthenium5 and other precious metals are often essential to ensure high performance. There is much interest in replacing these scarce elements with Earth-abundant metals, with iron6 and copper7 being particularly attractive owing to their low cost and non-toxicity. But despite the exploration of innovative molecular designs6,8,9,10, it remains a formidable scientific challenge11 to access Earth-abundant transition-metal complexes with long-lived charge-transfer excited states. No known iron complexes are considered12 photoluminescent at room temperature, and their rapid excited-state deactivation precludes their use as photosensitizers13,14,15. Here we present the iron complex [Fe(btz)3]3+ (where btz is 3,3′-dimethyl-1,1′-bis(p-tolyl)-4,4′-bis(1,2,3-triazol-5-ylidene)), and show that the superior σ-donor and π-acceptor electron properties of the ligand stabilize the excited state sufficiently to realize a long charge-transfer lifetime of 100 picoseconds (ps) and room-temperature photoluminescence. This species is a low-spin Fe(iii) d5 complex, and emission occurs from a long-lived doublet ligand-to-metal charge-transfer (2LMCT) state that is rarely seen for transition-metal complexes4,16,17. The absence of intersystem crossing, which often gives rise to large excited-state energy losses in transition-metal complexes, enables the observation of spin-allowed emission directly to the ground state and could be exploited as an increased driving force in photochemical reactions on surfaces. These findings suggest that appropriate design strategies can deliver new iron-based materials for use as light emitters and photosensitizers.
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| 6. |
- Chábera, Pavel, et al.
(författare)
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Band-selective dynamics in charge-transfer excited iron carbene complexes
- 2019
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Ingår i: Faraday Discussions. - : Royal Society of Chemistry (RSC). - 1359-6640 .- 1364-5498. ; 216:2019, s. 191-210
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Tidskriftsartikel (refereegranskat)abstract
- Ultrafast dynamics of photoinduced charge transfer processes in light-harvesting systems based on Earth-abundant transition metal complexes are of current interest for the development of molecular devices for solar energy conversion applications. A combination of ultrafast spectroscopy and first principles quantum chemical calculations of a recently synthesized iron carbene complex is used to elucidate the ultrafast excited state evolution processes in these systems with particular emphasis on investigating the underlying reasons why these complexes show promise in terms of significantly extended lifetimes of charge transfer excited states. Together, our results challenge the traditional excited state landscape for iron-based light harvesting transition metal complexes through radically different ground and excited state properties in alternative oxidation states. This includes intriguing indications of rich band-selective excited state dynamics on ultrafast timescales that are interpreted in terms of excitation energy dependence for excitations into a manifold of charge-transfer states. Some implications of the observed excited state properties and photoinduced dynamics for the utilization of iron carbene complexes for solar energy conversion applications are finally discussed.
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| 7. |
- Chábera, Pavel, et al.
(författare)
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FeII Hexa N-Heterocyclic Carbene Complex with a 528 ps Metal-To-Ligand Charge-Transfer Excited-State Lifetime
- 2018
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Ingår i: Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 9:3, s. 459-463
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Tidskriftsartikel (refereegranskat)abstract
- The iron carbene complex [FeII(btz)3](PF6)2 (where btz = 3,3′-dimethyl-1,1′-bis(p-Tolyl)-4,4′-bis(1,2,3-Triazol-5-ylidene)) has been synthesized, isolated, and characterized as a low-spin ferrous complex. It exhibits strong metal-To-ligand charge transfer (MLCT) absorption bands throughout the visible spectrum, and excitation of these bands gives rise to a 3MLCT state with a 528 ps excited-state lifetime in CH3CN solution that is more than one order of magnitude longer compared with the MLCT lifetime of any previously reported FeII complex. The low potential of the [Fe(btz)3]3+/[Fe(btz)3]2+ redox couple makes the 3MLCT state of [FeII(btz)3]2+ a potent photoreductant that can be generated by light absorption throughout the visible spectrum. Taken together with our recent results on the [FeIII(btz)3]3+ form of this complex, these results show that the FeII and FeIII oxidation states of the same Fe(btz)3 complex feature long-lived MLCT and LMCT states, respectively, demonstrating the versatility of iron N-heterocyclic carbene complexes as promising light-harvesters for a broad range of oxidizing and reducing conditions.
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| 8. |
- Chábera, Pavel, et al.
(författare)
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Photofunctionality of iron(III) N-heterocyclic carbenes and related d5 transition metal complexes
- 2021
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Ingår i: Coordination Chemistry Reviews. - : Elsevier BV. - 0010-8545. ; 426
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Forskningsöversikt (refereegranskat)abstract
- Despite a few reports of photoluminescent and strongly photo-oxidizing transition metal complexes with a d5 electronic configuration, the photophysics and photochemistry of this class of transition metal complexes have largely remained unexplored. Recent investigations of earth-abundant iron(III) N-heterocyclic carbene (NHC) complexes have demonstrated promising photophysical and photochemical properties associated with low-spin (doublet) ligand-to-metal charge transfer (2LMCT) excitations, including nanosecond photoluminescence (PL) and capabilities to drive both photo-oxidation and photo-reduction reactions. These encouraging results are at first sight surprising in light of the general scarcity of known photofunctional complexes of any transition metal complexes with a d5 electronic configuration, including 1st, 2nd and 3rd row transition metal complexes of Mn(II), Tc(II), Re(II), Fe(III), Ru(III) and Os(III). Here, we review the photophysical and photochemical properties of the new Fe(III) NHC complexes together with related d5 transition metal complexes as a basis for a broader understanding of the unorthodox photophysical and photochemical properties associated with this open-shell electronic configuration. This includes considerations of the role of charge and spin effects on the ground state electronic structure, as well as discussions of charge transfer (CT) and metal centered (MC) excited state properties. The special properties of 2LMCT excited states are emphasized as a key feature to understand the photophysics of many photofunctional d5 transition metal complexes. Further aspects of excited state dynamics with d5 light-harvesting complexes, including both intra- and inter-molecular charge transfer processes, are also discussed. Finally, some fundamental challenges and emerging opportunities for further development of photofunctional Fe(III) NHC and related LMCT/d5 complexes for light-harvesting, light-emitting, and photo(electro)chemical applications are outlined. This includes some general considerations of how the specific photochemical properties of the LMCT/d5 complexes provides an exciting opportunity to develop a unique niche within the diversity of photofunctional molecular systems alongside other types of organic and inorganic chromophores commonly used in the field of molecular photochemistry.
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| 9. |
- El Nahhas, Amal, et al.
(författare)
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Synthesis and Characterization of Cyclopentadithiophene Heterofulvenes : Design Tools for Light-Activated Processes
- 2017
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Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 23:24, s. 5673-5677
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Tidskriftsartikel (refereegranskat)abstract
- The development of new materials for solar-to-energy conversion should consider stability, ease of fabrication, and beneficial photophysical properties. In this context, a set of novel π-conjugated building blocks, with phospha- and arsaalkenes possessing a unique dithienyl annulated heterofulvenoid core, have been prepared as air- and moisture-stable sensitizers. These compounds unify electron-donor and -acceptor moieties, making them potential candidates for light-harvesting applications. Optical characterization of these systems was performed by steady-state and time-resolved absorption spectroscopy, supported by time-dependent DFT calculations. Tuning of the optical properties of these systems can be achieved by varying the pnictogen element at the bridgehead position, giving a bathochromic shift of ≈40 nm and coordinating the phosphaalkene towards gold AuI centers. The latter results in a ≈2000-fold extension of the ≈10 ps lifetime of uncoordinated systems well into the ns regime.
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| 10. |
- Ericson, Fredric, et al.
(författare)
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Electronic structure and excited state properties of iron carbene photosensitizers - A combined X-ray absorption and quantum chemical investigation
- 2017
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Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614. ; 683, s. 559-566
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Tidskriftsartikel (refereegranskat)abstract
- The electronic structure and excited state properties of a series of iron carbene photosensitizers are elucidated through a combination of X-ray absorption measurements and density functional theory calculations. The X-ray absorption spectra are discussed with regard to the unusual bonding environment in these carbene complexes, highlighting the difference between ferrous and ferric carbene complexes. The valence electronic structure of the core excited FeIII-3d5 complex is predicted by calculating the properties of a CoIII-3d6 carbene complex using the Z+1 approximation. Insight is gained into the potential of sigma-donating ligands as strategy to tune properties for light harvesting applications.
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