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Electron delocalization in the S1 and T1 metal-to-ligand charge transfer states of trans-substituted metal quadruply bonded complexes.

ABSTRACT: The singlet S(1) and triplet T(1) photoexcited states of the compounds containing MM quadruple bonds trans-M(2)(T(i)PB)(2)(O(2)CC(6)H(4)-4-CN)(2), where T(i)PB = 2,4,6-triisopropylbenzoate and M = Mo (I) or M = W (I(')), and trans-M(2)(O(2)CMe)(2)((N[(i) Pr ])(2)CC ? CC(6)H(5))(2), where M = Mo (II) and M = W (II(')), have been investigated by a variety of spectroscopic techniques including femtosecond time-resolved infrared spectroscopy. The singlet states are shown to be delocalized metal-to-ligand charge transfer (MLCT) states for I and I(') but localized for II and II(') involving the cyanobenzoate or amidinate ligands, respectively. The triplet states are MoMo??* for both I and II but delocalized (3)MLCT for I(') and localized (3)MLCT for II('). These differences arise from consideration of the relative orbital energies of the M(2)? or M(2)?* and the ligand ?(?) as well as the magnitudes of orbital overlap.

SUBMITTER: Alberding BG

PROVIDER: S-EPMC3100943 | biostudies-literature | 2011 May

REPOSITORIES: biostudies-literature

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Electron delocalization in the S1 and T1 metal-to-ligand charge transfer states of trans-substituted metal quadruply bonded complexes.

Alberding Brian G BG Chisholm Malcolm H MH Gallucci Judith C JC Ghosh Yagnaseni Y Gustafson Terry L TL

Proceedings of the National Academy of Sciences of the United States of America 20110427 20

The singlet S(1) and triplet T(1) photoexcited states of the compounds containing MM quadruple bonds trans-M(2)(T(i)PB)(2)(O(2)CC(6)H(4)-4-CN)(2), where T(i)PB = 2,4,6-triisopropylbenzoate and M = Mo (I) or M = W (I(')), and trans-M(2)(O(2)CMe)(2)((N[(i) Pr ])(2)CC ≡ CC(6)H(5))(2), where M = Mo (II) and M = W (II(')), have been investigated by a variety of spectroscopic techniques including femtosecond time-resolved infrared spectroscopy. The singlet states are shown to be delocalized metal-to-l ...[more]

PMID: 21525414

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Project description:In any physicochemical process in liquids, the dynamical response of the solvent to the solutes out of equilibrium plays a crucial role in the rates and products: the solvent molecules react to the changes in volume and electron density of the solutes to minimize the free energy of the solution, thus modulating the activation barriers and stabilizing (or destabilizing) intermediate states. In charge transfer (CT) processes in polar solvents, the response of the solvent always assists the formation of charge separation states by stabilizing the energy of the localized charges. A deep understanding of the solvation mechanisms and time scales is therefore essential for a correct description of any photochemical process in dense phase and for designing molecular devices based on photosensitizers with CT excited states. In the last two decades, with the advent of ultrafast time-resolved spectroscopies, microscopic models describing the relevant case of polar solvation (where both the solvent and the solute molecules have a permanent electric dipole and the mutual interaction is mainly dipole-dipole) have dramatically progressed. Regardless of the details of each model, they all assume that the effect of the electrostatic fields of the solvent molecules on the internal electronic dynamics of the solute are perturbative and that the solvent-solute coupling is mainly an electrostatic interaction between the constant permanent dipoles of the solute and the solvent molecules. This well-established picture has proven to quantitatively rationalize spectroscopic effects of environmental and electric dynamics (time-resolved Stokes shifts, inhomogeneous broadening, etc.). However, recent computational and experimental studies, including ours, have shown that further improvement is required. Indeed, in the last years we investigated several molecular complexes exhibiting photoexcited CT states, and we found that the current description of the formation and stabilization of CT states in an important group of molecules such as transition metal complexes is inaccurate. In particular, we proved that the solvent molecules are not just spectators of intramolecular electron density redistribution but significantly modulate it. Our results solicit further development of quantum mechanics computational methods to treat the solute and (at least) the closest solvent molecules including the nonperturbative treatment of the effects of local electrostatics and direct solvent-solute interactions to describe the dynamical changes of the solute excited states during the solvent response.

Dataset Information

Electron delocalization in the S1 and T1 metal-to-ligand charge transfer states of trans-substituted metal quadruply bonded complexes.

Publications

Electron delocalization in the S1 and T1 metal-to-ligand charge transfer states of trans-substituted metal quadruply bonded complexes.

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