Conformational Dependence of σ‐Electron Delocalization in Linear Chains: Permethylated Oligosilanes

Bande, Annika; Michl, Josef

doi:10.1002/chem.200901521

Cited by 64 publications

(92 citation statements)

References 81 publications

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“…In oligosilanes with a non-planar skeleton of silicon atoms excited states of strongly mixed nature are also possible but are relatively rare. This is especially true in the alltransoid conformers, whose silicon skeleton is almost planar and the σσ*, σπ* nomenclature quite satisfactory 10 . The lowest σ* and π* MOs in peralkylated oligosilanes are of comparable energy and one or the other is the lowest unoccupied molecular orbital (LUMO).…”

Section: Molecular Orbitals and Excited States In Saturated Systemsmentioning

confidence: 98%

“…Although all valence excitation in saturated systems without lone pairs, such as the oligosilanes, necessarily is from bonding orbitals of σ type to antibonding orbitals of σ* type, it is useful to distinguish two types of delocalized molecular orbitals (MOs) in an oligosilane chain 6,10 . Those that are symmetric with respect to the local Si-Si-Si plane are said to be of local σ character and those that are locally antisymmetric, of local π character.…”

Section: Molecular Orbitals and Excited States In Saturated Systemsmentioning

confidence: 99%

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Why do disilanes fail to fluoresce?

MacLeod

Michl

2011

Collect. Czech. Chem. Commun.

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In contrast to longer peralkylated oligosilanes, many of which fluoresce efficiently, disilanes and trisilanes exhibit no detectable fluorescence even at low temperatures. This is especially striking in the case of disilanes, whose S 1 -S 0 transition is quite strongly allowed, and which must have very efficient electronic excited state deactivation mechanisms. To identify them, we examine the lowest excited singlet state potential energy surface S 1 of Si 2 Me 6 with TDDFT (B3LYP/TZVP, PBE0/TZVP and BHLYP/TZVP) and ab initio (RICC2/TZVP and RIADC(2)/TZVP) methods and identify several shallow minima and nearby funnels. Relaxed excited state structures show strong valence rehybridization relative to the ground state, allowing optimal accomodation of the simultaneous presence of a negative and a positive charge in their Lewis structures. Efficient decay pathways and relations to longer oligosilanes are discussed.

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Section: Molecular Orbitals and Excited States In Saturated Systemsmentioning

confidence: 98%

Section: Molecular Orbitals and Excited States In Saturated Systemsmentioning

confidence: 99%

Why do disilanes fail to fluoresce?

MacLeod

Michl

2011

Collect. Czech. Chem. Commun.

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“…The coupling, however, could be lifted through rotation of the fragments against each other as has been, e.g., analyzed before in the context of  electron delocalization in permethylated oligosilanes. [29] There, it was shown by a theoretical rationalization that occupied and unoccupied orbitals with  bond character and hence * excitations depend strongly on the dihedral angles along the bonds separating two identical polysilane fragments. Two aspects from that piece of research find their counterparts here: rotation effects and orbital splitting.…”

Section: Ii3 Biuretmentioning

confidence: 99%

Analysis of the Electronic Structure of Aqueous Urea and Its Derivatives: A Systematic Soft X‐Ray–TD‐DFT Approach

Tesch

Golnak

Ehrhard

et al. 2016

Chemistry A European J

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Soft X-ray emission, absorption, and resonant inelastic scattering experiments have been conducted at the nitrogen K-edge of urea and its derivatives in aqueous solutions and compared with density functional theory and time-dependent density functional theory calculations. This comprehensive study provides detailed information on the occupied and unoccupied molecular orbitals of urea, thiourea, acetamide, dimethylurea and biuret at valence levels. By identifying the electronic transitions that contribute to the experimental spectral features the energy gap between the highest occupied and the lowest unoccupied molecular orbital of each molecule is determined. Moreover, a theoretical approach is introduced to simulate resonant inelastic X-ray scattering spectra by adding an extra electron to the lowest unoccupied molecular orbital mimicking the real initial state of the core electron absorption before the subsequent relaxation process.

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“…Other models, such as Sandorfy H, account for the LUMO, focusing on the interaction between the backbone and substituent orbitals [13]. Elaborations on these descriptive models have shown that the simple intuitions of HMO theory still hold [30]. By employing ab initio methods such as DFT where the effective core potentials of tin are accounted for, structure predictions can be made without the requirement of existing experimental data [31].…”

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confidence: 99%

Linear Oligostannanes: A Synthetic and TD-DFT Study

Harrypersad

Liao

Khan

et al. 2015

J Inorg Organomet Polym

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A series of model linear tristannanes [(( 1 R) 3-Sn) 2 ( 2 R) 2 Sn (1: 1 R = 2 R = n-Bu, 2: 1 R = Ph, 2 R = n-Bu, 3: 1 R = Me, 2 R = n-Bu, 4: 1 R = n-Bu, 2 R = Ph, 5: 1 R = Me, 2 R = Ph, 6: 1 R = n-Bu, 2 R = Me, 7: 1 R = Ph, 2 R = Me)] were prepared by condensation reactions of one equivalent of a dialkyl or diaryl tin diamide or dihydride and two equivalents of a trialkyl or triaryl tin hydride or amide respectively, and characterized by NMR ( 1 H, 13 C, 119 Sn) and UV-Vis spectroscopy, and elemental analysis. An LSDA/SDD level of DFT and TD-DFT for trimers 1-7 predicts significant structural differences as a function and nature of the substituents bound to tin and calculated electronic transitions for these compounds in fair relative agreement with experimental results. Calculated electronic spectra obtained from equivalent DFT studies of the sequentially lengthened oligomers Ph 3 Sn[t-Bu 2 Sn] n SnPh 3 (8-11 where n = 1-4) previously prepared by Dräger are in good agreement with the reported experimental UVVisible spectroscopic and X-ray diffraction data which show a red shift of the r-r* absorption transition (k max ) and bond lengthening and bond angle widening of the central tin atoms as the oligostannane is extended. TD-DFT studies of the alkoxy terminated di(n-butyl) oligostannanes 12a-m (CH 3 CH 2 OCH 2 CH 2 [Sn(n-Bu) 2 ] n CH 2 CH 2 OCH 2 CH 3 ); n = 3-15) indicate lower limiting energy gaps as the polymer chain size is increased. The calculated data deviates significantly from results found experimentally by Sita and suggests that even smaller energy gaps are possible if the polymer (13) resides in an all trans configuration. TD-DFT studies at the LSDA/SDD level were also carried out on a model polystannane 16 (H[SnH 2 ] n H, n = 1-40) to investigate the impact of Sn catenation on the intrinsic band gap of the material and compared to both the Si and Ge analogues 14 and 15 (H[MH 2 ] n H, M = Si, Ge: n = 1-40). The modelling of the polymetallanes reveals the expected limiting energy gap of the r-r* transition in a trans-planar configuration with Sn (2.681 eV) \ Ge (3.096 eV) \ Si (3.719 eV) in good agreement with previous studies by Takeda. Finally, comparison of the TD-DFT calculated data for model alternating oligostannanes (17)(18)(19) with the UV-Vis spectroscopic data for alternating polystannanes (20-22) recently prepared by polycondensation is made.

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Conformational Dependence of σ‐Electron Delocalization in Linear Chains: Permethylated Oligosilanes

Cited by 64 publications

References 81 publications

Why do disilanes fail to fluoresce?

Why do disilanes fail to fluoresce?

Analysis of the Electronic Structure of Aqueous Urea and Its Derivatives: A Systematic Soft X‐Ray–TD‐DFT Approach

Linear Oligostannanes: A Synthetic and TD-DFT Study

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