Ultrafast Intramolecular Charge Separation in a Donor鈥揂cceptor Assembly Comprising Bis(畏5-cyclopentadienyl)molybdenum Coordinated to an Ene-1,2-dithiolate-naphthalenetetracarboxylicdiimide

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• 作者：Adam J. Taylor ; E. Stephen Davies ; Julia A. Weinstein ; Igor V. Sazanovich ; Oleg V. Bouganov ; Sergei A. Tikhomirov ; Michael Towrie ; Jonathan McMaster ; C. David Garner
• 刊名：Inorganic Chemistry
• 出版年：2012
• 出版时间：December 17, 2012
• 年：2012
• 卷：51
• 期：24
• 页码：13181-13194
• 全文大小：594K
• 年卷期：v.51,no.24(December 17, 2012)
• ISSN：1520-510X

文摘

The first example of a Donor-spacer-Acceptor tryad, based upon a molybdenum-ene-1,2-dithiolate unit as the Donor and a naphthalene-diimide as the Acceptor, has been synthesized and its photophysical properties investigated. Synthesis required the preparation of a new pro-ligand containing a protected ene-1,2-dithiolate bound through a phenyl linkage to a naphthalenetetracarboxylicdiimide (NDI) group. Deprotection of this pro-ligand by base hydrolysis, followed by reaction with [Cp₂MoCl₂], produced the new dyad [Cp₂Mo(SC(H)C(C₆H₄鈥揘DI)S)] (2). Electrochemical studies showed that 2 can be reversibly oxidized to [2]⁺ and reduced to [2]^{鈭?/sup>, [2]2鈥?/sup>, and [2]3鈥?/sup>. These studies, augmented by UV/vis, IR, and electron paramagnetic resonance (EPR) spectra of electrochemically generated [2]+ and [2]鈭?/sup>, show that the highest occupied molecular orbital (HOMO) of 2 is ene-1,2-dithiolate-based and the lowest unoccupied molecular orbital (LUMO) is NDI-based; these conclusions are supported by density functional theory (DFT) calculations for the electronic ground state on a model of 2 which also showed that these two parts of the molecule are electronically distinct. The dynamics of the excited states of 2 in CH₂Cl₂ solution were investigated by picosecond time-resolved IR spectroscopy following irradiation by a 400 nm 120 fs laser pulse. These investigations were complemented by an ultrafast transient absorption spectroscopic study from 420 to 760 nm of the nature of the excited states of 2 in CH₂Cl₂ solution following irradiation by a 383 nm 120 fs laser pulse. These studies showed that irradiation of 2 at both 400 and 383 nm leads to the formation of the [(Cp)₂{Mo(dt)}+-Ph-{NDI}鈭?/sup>] charge-separated state as a result of a cascade electron transfer initiated by the formation of an 1NDI* excited state. 1NDI* rapidly (ca. 0.2 ps) forms the local charge transfer state [Cp₂Mo(dt)-{Ph}+-{NDI}鈭?/sup>] which has a lifetime of about 1.7 ps and decays to produce the ground state and the charge-separated state [(Cp)₂{Mo(dt)}+路-Ph-{NDI}鈭?/sup>]; the latter has an appreciable lifetime, about 15 ns in CH₂Cl₂ at room temperature.}