| 1. |
- 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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| 2. |
- Kulshreshtha, Chandramouli, et al.
(författare)
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Investigating ultrafast carrier dynamics in perovskite solar cells with an extended π-conjugated polymeric diketopyrrolopyrrole layer for hole transportation
- 2020
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Ingår i: RSC Advances. - : Royal Society of Chemistry. - 2046-2069. ; 10:11, s. 6618-6624
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Tidskriftsartikel (refereegranskat)abstract
- Here, we show a new diketopyrrole based polymeric hole-transport material (PBDTP-DTDPP, (poly[[2,5-bis(2-hexyldecyl)-2,3,5,6-tetrahydro-3,6-dioxopyrrolo[3,4-c]pyrrole-1,4-diyl]-alt-[[2,2′-(4,8-bis(4-ethylhexyl-1-phenyl)-benzo[1,2-b:4,5-b′]dithiophene)bis-thieno[3,2-b]thiophen]-5,5′-diyl]])) for application in perovskite solar cells. The material performance was tested in a solar cell with an optimized configuration, FTO/SnO2/perovskite/PBDTP-DTDPP/Au, and the device showed a power conversion efficiency of 14.78%. The device charge carrier dynamics were investigated using transient absorption spectroscopy. The charge separation and recombination kinetics were determined in a device with PBDTP-DTDPP and the obtained results were compared to a reference device. We find that PBDTP-DTDPP enables similar charge separation time (<∼4.8 ps) to the spiro-OMeTAD but the amount of nongeminate recombination is different. Specifically, we find that the polymeric PBDTP-DTDPP hole-transport layer (HTL) slows-down the second-order recombination much less than spiro-OMeTAD. This effect is of particular importance in studying the charge transportation in optimized solar cell devices with diketopyrrole based HTL materials.
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| 3. |
- Kunnus, Kristjan, et al.
(författare)
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Vibrational wavepacket dynamics in Fe carbene photosensitizer determined with femtosecond X-ray emission and scattering
- 2020
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Ingår i: Nature Communications. - : Springer Nature. - 2041-1723. ; 11:1
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Tidskriftsartikel (refereegranskat)abstract
- The non-equilibrium dynamics of electrons and nuclei govern the function of photoactive materials. Disentangling these dynamics remains a critical goal for understanding photoactive materials. Here we investigate the photoinduced dynamics of the [Fe(bmip)2]2+ photosensitizer, where bmip = 2,6-bis(3-methyl-imidazole-1-ylidine)-pyridine, with simultaneous femtosecond-resolution Fe Kα and Kβ X-ray emission spectroscopy (XES) and X-ray solution scattering (XSS). This measurement shows temporal oscillations in the XES and XSS difference signals with the same 278 fs period oscillation. These oscillations originate from an Fe-ligand stretching vibrational wavepacket on a triplet metal-centered (3MC) excited state surface. This 3MC state is populated with a 110 fs time constant by 40% of the excited molecules while the rest relax to a 3MLCT excited state. The sensitivity of the Kα XES to molecular structure results from a 0.7% average Fe-ligand bond length shift between the 1 s and 2p core-ionized states surfaces.
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| 4. |
- Lindh, Linnea, et al.
(författare)
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Photophysics and photochemistry of iron carbene complexes for solar energy conversion and photocatalysis
- 2020
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Ingår i: Catalysts. - : MDPI AG. - 2073-4344. ; 10:3
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Forskningsöversikt (refereegranskat)abstract
- Earth-abundant first row transition metal complexes are important for the development of large-scale photocatalytic and solar energy conversion applications. Coordination compounds based on iron are especially interesting, as iron is the most common transition metal element in the Earth’s crust. Unfortunately, iron-polypyridyl and related traditional iron-based complexes generally suffer from poor excited state properties, including short excited-state lifetimes, that make them unsuitable for most light-driven applications. Iron carbene complexes have emerged in the last decade as a new class of coordination compounds with significantly improved photophysical and photochemical properties, that make them attractive candidates for a range of light-driven applications. Specific aspects of the photophysics and photochemistry of these iron carbenes discussed here include long-lived excited state lifetimes of charge transfer excited states, capabilities to act as photosensitizers in solar energy conversion applications like dye-sensitized solar cells, as well as recent demonstrations of promising progress towards driving photoredox and photocatalytic processes. Complementary advances towards photofunctional systems with both Fe(II) complexes featuring metal-to-ligand charge transfer excited states, and Fe(III) complexes displaying ligand-to-metal charge transfer excited states are discussed. Finally, we outline emerging opportunities to utilize the improved photochemical properties of iron carbenes and related complexes for photovoltaic, photoelectrochemical and photocatalytic applications.
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| 5. |
- Tatsuno, Hideyuki, et al.
(författare)
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Hot Branching Dynamics in a Light-Harvesting Iron Carbene Complex Revealed by Ultrafast X-ray Emission Spectroscopy
- 2020
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Ingår i: Angewandte Chemie - International Edition. - : Wiley. - 1433-7851 .- 1521-3773. ; 59:1, s. 364-372
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Tidskriftsartikel (refereegranskat)abstract
- Iron N-heterocyclic carbene (NHC) complexes have received a great deal of attention recently because of their growing potential as light sensitizers or photocatalysts. We present a sub-ps X-ray spectroscopy study of an FeIINHC complex that identifies and quantifies the states involved in the deactivation cascade after light absorption. Excited molecules relax back to the ground state along two pathways: After population of a hot 3MLCT state, from the initially excited 1MLCT state, 30 % of the molecules undergo ultrafast (150 fs) relaxation to the 3MC state, in competition with vibrational relaxation and cooling to the relaxed 3MLCT state. The relaxed 3MLCT state then decays much more slowly (7.6 ps) to the 3MC state. The 3MC state is rapidly (2.2 ps) deactivated to the ground state. The 5MC state is not involved in the deactivation pathway. The ultrafast partial deactivation of the 3MLCT state constitutes a loss channel from the point of view of photochemical efficiency and highlights the necessity to screen transition-metal complexes for similar ultrafast decays to optimize photochemical performance.
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| 6. |
- Zigmantas, Donatas, et al.
(författare)
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Ultrafast laser spectroscopy uncovers mechanisms of light energy conversion in photosynthesis and sustainable energy materials
- 2022
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Ingår i: Chemical Physics Reviews. - : AIP Publishing. - 2688-4070. ; 3:4
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Tidskriftsartikel (refereegranskat)abstract
- The invention of the laser in 1960 gave us the ruby laser, which generally produced chaotic pulses of light. Six years later, in 1966, a concept called passive mode-locking applied to neodymium-glass lasers produced reasonably well-behaving picosecond pulses. This triggered an intense activity, with respect to developing improved laser pulse sources, measurement techniques, and application to chemistry, physics, and biology. Initially, only ∼10 –ps-long pulses at a few wavelengths were available. Nevertheless, insight into the function of complex biological systems, like photosynthetic proteins, and molecules of chemical interest was gained in very early studies. Today, both duration and color of ultrashort pulses can be tuned to almost any value. This has of course opened up possibilities to study almost any atomic, molecular, or solid-state system and any dynamic process. This review focuses on the use of laser spectroscopy to investigate light energy conversion mechanisms in both natural photosynthesis and a topical selection of novel materials for solar energy conversion. More specifically, in photosynthesis we will review light harvesting and primary electron transfer; materials for solar energy conversion that we discuss include sensitized semiconductors (dye sensitized solar cells), polymer:fullerene and polymer:polymer bulk heterojunctions (organic solar cells), organometal halide perovskites, as well as molecular and hybrid systems for production of solar fuel and valuable chemicals. All these scientific areas, and in particular photosynthesis and the solar cell materials, have been extensively studied with ultrafast spectroscopy, resulting in a vast literature; a comprehensive review of the individual materials is, therefore, not feasible, and we will limit our discussion to work that we think has been of particular importance for understanding the function of the respective systems.
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