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Excited-State Bond Contraction and Charge Migration in a Platinum Dimer Complex Characterized by X-ray and Optical Transient Absorption Spectroscopy. J Phys Chem A 2021; 125:8891-8898. [PMID: 34597043 DOI: 10.1021/acs.jpca.1c07201] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Interactions between metal centers in dimeric transition metal complexes (TMCs) play important roles in their excited-state energetics and pathways and, thus, affect their photophysical properties relevant to their applications, for example, photoluminescent materials and photocatalysis. Here, we report electronic and nuclear structural dynamics studies of two photoexcited pyrazolate-bridged [Pt(ppy)(μ-R2pz)]2-type Pt(II) dimers (ppy = 2-phenylpyridine, μ-R2pz = 3,5-substituted pyrazolate): [Pt(ppy)(μ-H2pz)]2 (1) and [Pt(NDI-ppy)(μ-Ph2pz)]2 (2, NDI = 1,4,5,8-naphthalenediimide), both of which have distinct ground-state Pt-Pt distances. X-ray transient absorption (XTA) spectroscopy at the Pt LIII-edge revealed a new d-orbital vacancy due to the one-electron oxidation of the Pt centers in 1 and 2. However, while a transient Pt-Pt contraction was observed in 2, such an effect was completely absent in 1, demonstrating how the excited states of these complexes are determined by the overlap of the Pt (dz2) orbitals, which is tuned by the steric bulk of the pyrazolate R-groups in the 3- and 5-positions. In tandem with analysis of the Pt-Pt distance structural parameter, we observed photoinduced electron transfer in 2 featuring a covalently linked NDI acceptor on the ppy ligand. The formation and subsequent decay of the NDI radical anion absorption signals were detected upon photoexcitation using optical transient absorption spectroscopy. The NDI radical anion decayed on the same time scale, hundreds of picoseconds, as that of the d-orbital vacancy signal of the oxidized Pt-Pt core observed in the XTA measurements. The data indicated an ultrafast formation of the charge-separated state and subsequent charge recombination to the original Pt(II-II) species.
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Probing Interligand Electron Transfer in the 1MLCT S1 Excited State of trans-Mo2L2L′2 Compounds: A Comparative Study of Auxiliary Ligands and Solvents. Inorg Chem 2017; 56:9660-9668. [DOI: 10.1021/acs.inorgchem.7b01164] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Can Excited State Electronic Coherence Be Tuned via Molecular Structural Modification? A First-Principles Quantum Electronic Dynamics Study of Pyrazolate-Bridged Pt(II) Dimers. J Phys Chem A 2017; 121:1932-1939. [DOI: 10.1021/acs.jpca.6b12099] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Probing the solvation structure and dynamics in ionic liquids by time-resolved infrared spectroscopy of 4-(dimethylamino)benzonitrile. Phys Chem Chem Phys 2017; 19:25151-25157. [DOI: 10.1039/c7cp04961g] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
In this work we demonstrate the use of the push–pull model system 4-(dimethylamino)benzonitrile (DMABN) as a convenient molecular probe to investigate the local solvation structure and dynamics by means of time-resolved infrared spectroscopy (TRIR).
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Tunable Excited-State Properties and Dynamics as a Function of Pt–Pt Distance in Pyrazolate-Bridged Pt(II) Dimers. J Phys Chem A 2016; 120:543-50. [DOI: 10.1021/acs.jpca.5b11233] [Citation(s) in RCA: 44] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
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Photophysical studies of metal to ligand charge transfer involving quadruply bonded complexes of molybdenum and tungsten. Acc Chem Res 2015; 48:877-85. [PMID: 25695495 DOI: 10.1021/ar500256f] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
Photoinduced metal-to-ligand charge transfer transitions afford numerous applications in terms of photon energy harvesting. The majority of metal complexes studied to date involve diamagnetic systems of d(6), d(8), and d(10) transition metals. These typically have very short-lived, ∼100 fs, singlet metal to ligand charge transfer ((1)MLCT) states that undergo intersystem crossing to triplet metal to ligand charge transfer ((3)MLCT) states that are longer lived and are responsible for much of the photophysical studies. In contrast, the metal-metal quadruply bonded complexes of molybdenum and tungsten supported by carboxylate, O2CR, and related amidinate ligands (RN)2C(R') have relatively long-lived (1)MLCT states arising from M2δ to Lπ* transitions. These have lifetimes in the range 1-20 ps prior to intersystem crossing to T1 states that may be (3)MLCT or (3)MMδδ* with lifetimes of 1-100 ns and 1-100 μs, respectively. The M2 quadruply bonded complexes take the form M2L4 or M2L4-nL'n where n = 1-3. Thus, in their photoexcited MLCT states, these compounds pose the question of how the charge resides on the ligands. This Account reviews the current knowledge of how charge is positioned with time in S1 and T1 states with the aid of active IR reported groups located on the ligands, for example, C≡X multiple bonds (X = C, N, or O). Several examples of localized and delocalized charge distributions are noted along with kinetic barriers to the interconversion of MLCT and δδ* states. On the 50th anniversary of the recognition of the MM quadruple bond, these complexes are revealing some remarkable features in the study of the photophysical properties of metal-ligand charge transfer states.
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MM Quadruply Bonded Complexes Supported by Vinylbenzoate Ligands: Synthesis, Characterization, Photophysical Properties and Application as Synthons. Chem Sci 2015; 6:1780-1791. [PMID: 26417424 PMCID: PMC4583209 DOI: 10.1039/c4sc02542c] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
MM complexes as potential synthons for the development of higher order extended structures via Heck coupling reactions, exhibiting interesting photophysical properties.
From the reactions between M2(TiPB)4 compounds and meta and para-vinylbenzoic acids (2 equiv.) in toluene at room temperature the compounds trans-M2(TiPB)2L2, where L = m-vinylbenzoate 1A (M = Mo) and 1B (M = W) and TiPB = 2,4,6-triisopropylbenzoate, and where L = p-vinylbenzoate 2A (M = Mo) and 2B (M = W) have been isolated. Compounds 1A and 2A have been shown to undergo Heck carbon–carbon coupling reactions with phenyliodide to produce trans-Mo2(TiPB)2(O2CC6H4-m-CH
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CH–C6H5)2, 3A and trans-Mo2(TiPB)2(O2CC6H4-p-CHCH–C6H5)2, 4A. The molybdenum compounds 1A and 2A have been structurally characterized by single crystal X-ray crystallography. All the new compounds have been characterized by 1H NMR, IR, UV-visible absorption and emission spectroscopy, high resolution MALDI-TOF MS, fs- and ns-transient absorption spectroscopy and fs-time-resolved IR spectroscopy. Electronic structure calculations employing density functional theory, DFT, and time-dependent DFT have been employed to aid in the interpretation of spectral data. All compounds show intense absorptions in the visible region corresponding to M2δ to Lπ* charge transfer transitions. The lifetimes of the 1MLCT state fall in the range of 1–10 ps and for the molybdenum complexes the T1 states are 3δδ* with lifetimes ∼50 μs while for the tungsten complexes the T1 are 3MLCT with lifetimes in the range of 3–10 ns.
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Correction to “Electronic Structure and Excited-State Dynamics of the Molecular Triads: trans-M 2(T iPB) 2[O 2CC 6H 5-η 6-Cr(CO) 3] 2, Where M = Mo or W, and T iPB = 2,4,6-triisopropylbenzoate”. J Am Chem Soc 2014. [DOI: 10.1021/ja505627v] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Photophysical Properties of cis-Mo2 Quadruply Bonded Complexes and Observation of Photoinduced Electron Transfer to Titanium Dioxide. J Am Chem Soc 2014; 136:11428-35. [DOI: 10.1021/ja504944d] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
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Molybdenum–molybdenum quadruple bonds supported by 9,10-anthraquinone carboxylate ligands. Molecular, electronic, ground state and unusual photoexcited state properties. Chem Sci 2014. [DOI: 10.1039/c4sc00341a] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
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Mo2 paddlewheel complexes functionalized with a single MLCT, S1 infrared-active carboxylate reporter ligand: preparation and studies of ground and photoexcited states. Inorg Chem 2013; 53:637-44. [PMID: 24359530 DOI: 10.1021/ic402775s] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
From the reactions between Mo2(DAniF)3pivalate (DAniF = N,N'-di(p-anisyl)formamidinate) and the carboxylic acids LH, the title compounds Mo2(DAniF)3L have been prepared and characterized: compounds I (L = O2CC≡CPh), II (L = O2CC4H2SC≡CH), and III (L = O2CC6H4-p-CN). The new compounds have been characterized in their ground states by spectroscopy ((1)H NMR, ultraviolet-visible absorption, near-infrared absorption, and steady state emission), cyclic voltammetry, and density functional theory calculations. The compounds show strong metal Mo2 to ligand L δ-π* transitions in their visible spectra. The nature of the S1 (1)MLCT and T1 states has been probed by time-resolved (femtosecond and nanosecond) transient absorption and infrared spectroscopy. The observed shifts of the C≡C and C≡N vibrational modes are found to be consistent with the negative charge being localized on the single L in the S1 states, while the T1 states are (3)Mo2 δδ*. The present results are compared to earlier studies of the photoexcited states of trans-Mo2(2,4,6-triisopropylbenzoate)2L2 compounds that have been assigned as either localized or delocalized.
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Concerning the Ground State and S1 and T1 Photoexcited States of the Homoleptic Quadruply Bonded Complexes Mo2(O2CC6H4-p-X)4, where X = C≡C–H or C≡N. J Phys Chem A 2013; 117:13893-8. [PMID: 24205848 DOI: 10.1021/jp408667m] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Modulating the M2δ-to-ligand charge transfer transition by the use of diarylboron substituents. Dalton Trans 2013; 42:14491-7. [PMID: 23969875 DOI: 10.1039/c3dt51684a] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
From the reactions between the quadruply bonded complexes M2(T(i)PB)4, where M = Mo or W and T(i)PB = 2,4,6-triisopropylbenzoate, and the carboxylic acids HOOC-C6H4-4-B(mesityl)2, LH (2 equivalents) the complexes trans-M2(T(i)PB)2L2 have been prepared. The new compounds have been characterized by (1)H NMR, MALDI-TOF MS, UV-Vis-NIR and steady-state emission spectroscopy, time-resolved transient absorption spectroscopy and cyclic voltammetry. These results are compared with the related properties of the benzoates, M2(T(i)PB)2(O2CPh)2 (prepared similarly) and with DFT calculations on model compounds where formate substitutes for T(i)PB. The new compounds M2(T(i)PB)2L2 are intensely colored in toluene or THF solutions: red (M = Mo) and green (M = W) and the introduction of the p-B(mesityl)2 group notably shifts these metal to ligand charge transfer transitions to lower energy in comparison to the benzoate complexes M2(T(i)PB)2(O2C-C6H5)2. Upon the addition of fluoride ions these intense absorptions are shifted to much higher energy in a reversible manner for M = Mo.
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Metal-metal quadruple bonds supported by 5-ethynylthiophene-2-carboxylato ligands: preparation, molecular and electronic structures, photoexcited state dynamics, and application as molecular synthons. J Am Chem Soc 2013; 135:8254-9. [PMID: 23705765 DOI: 10.1021/ja400508u] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
From the reaction between M2(T(i)PB)4 and 2 equiv of 5-ethynylthiophene-2-carboxylic acid (H-ThCCH) in toluene, the complexes trans-M2(T(i)PB)2(ThCCH)2, where M = Mo (I) or W (II) and T(i)PB = 2,4,6-triisopropyl benzoate, have been isolated and characterized by (1)H NMR, IR, MALDI-TOF MS, UV-vis, steady-state emission, transient absorption, and time-resolved infrared (TRIR) spectroscopies and single-crystal X-ray crystallography for I. The molecular structure of I confirms the trans-substitution pattern and the extended conjugation of the ethynylthienyl ligands via interaction with the Mo2δ orbital. The HOMO of both I and II is the M2δ orbital, and the intense color of the compounds (I is red and II is blue) is due to the M2δ-to-ThCCH (1)MLCT transition. The S1 states for I and II are (1)MLCT. The T1 state is (3)MLCT for II, but (3)MoMoδδ* for I. The TRIR spectra of the ν(C≡C) stretch in the MLCT states are consistent with the delocalization of the electron over both ThCCH ligands. Compound I is shown to be a synthon for the preparation of trans-Mo2(T(i)PB)2(ThCCPh)2 (III) and trans-Mo2(T(i)PB)2(ThCCAuPPh3)2 (IV). Both III and IV have been characterized spectroscopically and by single-crystal X-ray diffraction. The structure of III indicates the extended π-conjugation of the trans-ethynyl-thienyl units extends to the added phenyl rings.
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Coordination of N,N-Chelated Re(CO)3Cl Units Across a Mo2 Quadruple Bond: Synthesis, Characterization, and Photophysical Properties of a Re–Mo2–Re Triad and Its Component Pieces. J Phys Chem A 2013; 117:5997-6006. [DOI: 10.1021/jp311830h] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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MM quadruple bonds supported by cyanoacrylate ligands. Extending photon harvesting into the near infrared and studies of the MLCT states. Chem Sci 2013. [DOI: 10.1039/c3sc50322d] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
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Photoinduced charge transfer involving a MoMo quadruply bonded complex to a perylene diimide. Dalton Trans 2013; 42:5275-80. [DOI: 10.1039/c3dt32750g] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Electronic Structure and Excited-State Dynamics of the Molecular Triads: trans-M2(TiPB)2[O2CC6H5-η6-Cr(CO)3]2, Where M = Mo or W, and TiPB = 2,4,6-triisopropylbenzoate. J Am Chem Soc 2012. [DOI: 10.1021/ja310651y] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Furan- and selenophene-2-carboxylato derivatives of dimolybdenum and ditungsten (M[quadruple bond]M): a comparison of their chemical and photophysical properties. Dalton Trans 2012; 41:2257-63. [PMID: 22186951 DOI: 10.1039/c1dt11889g] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
From the reactions between M(2)(T(i)PB)(4), where T(i)PB = 2,4,6-triisopropylbenzoate and two equivalents each of 2-furan carboxylic acid, FuCO(2)H, and 2-selenophene carboxylic acid, SpCO(2)H in toluene, the new compounds trans-M(2)(T(i)PB)(2)(O(2)CFu)(2) (1a M = Mo, 2a M = W) and trans-M(2)(T(i)PB)(2)(O(2)CSp)(2) (1b M = Mo, 2b M = W) were formed. These new compounds have been characterized by (1)H NMR, steady-state UV-Vis-NIR absorption and emission spectroscopy, cyclic and differential pulse voltammetry, and fs and ns transient absorption spectroscopy. The compound Mo(2)(T(i)PB)(2)(O(2)CSp)(2) (1b) has been characterized by single crystal X-ray crystallography. These data are compared with those previously reported for related 2-thiophene carboxylate derivatives: M(2)(T(i)PB)(2)(O(2)CTh)(2). The physico-chemical data correlate well with electronic structure calculations performed on model compounds. All compounds have detectible S(1) photoexcited states with lifetimes that vary from ∼5 ps to < 1 ps. The molybdenum compounds have T(1) states with microsecond lifetimes that are assigned as MMδδ* whereas the T(1) states for tungsten are (3)MLCT with lifetimes on the order of nanoseconds. In all cases, shorter lifetimes were seen in complexes containing heavier atoms.
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Molecular and electronic structures and photophysical properties of quadruply bonded dimetal complexes (M = Mo or W) supported by trans-arylethynylcarboxylate ligands where aryl = p-tolyl or 9-anthrancenyl. Dalton Trans 2012; 41:12270-81. [DOI: 10.1039/c2dt31359f] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
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Photophysical properties of MM quadruply bonded complexes (M = Mo, W) supported by carboxylate ligands: charge delocalization and dynamics in S1 and T1 states. Dalton Trans 2012; 41:13097-104. [DOI: 10.1039/c2dt30490b] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
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