Charge-Transfer States in Boranes and Carbonium Ions. Their Ultraviolet Spectra

Ramsey, Brian G.

doi:10.1021/j100875a002

Cited by 42 publications

(18 citation statements)

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“…The calculated energies for 2-5, the ionization potentials for 2 and 4, and the harmonic frequencies for 2 and 3 are given in Tables I, II, and III, respectively. Tetrasilabicyclo[ 1.1.0]butane (2). Structure and Bonding.…”

Section: Resultsmentioning

confidence: 99%

The structure and barrier to inversion of tetrasilabicyclo[1.1.0]butane. Comparison to bicyclo[1.1.0]butane

Collins¹,

Dutler²,

Rauk³

1987

J. Am. Chem. Soc.

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The equilibrium geometry of tetrasilabicyclo[ 1.1 .O]butane, as determined by full gradient optimization at the RHF level of theory by using 6-31G* basis set, has C2, symmetry. The two Si-Si bond lengths are 2.304 and 2.370 A, the latter being the bond connecting the bridgehead atoms. The dihedral angle between the two rings is 122.9O. The corresponding bonds of the transition structure for ring inversion, which has D2,, symmetry, are 2.295 and 2.805 A, respectively. The barrier to ring inversion is calculated to be 75 kJ mol-' after correction for correlation energy differences up to MP3 and inclusion of zero-point vibrational energies. The bond connecting the bridgehead atoms is not broken but changes from a bent u bond at the equilibrium geometry to a a bond in the transition structure. By contrast, bicyclo[l.l.O]butane suffers bond rupture during inversion, the transition structure being most probably a triplet diradical. The inversion barrier, estimated to be about 300 kJ mol-', is higher than that required for the sigmatropic rearrangement to butadiene. The origin of the differences between the C and Si analogues is discussed.Interest in the properties and preparation of strain decyclic polysilanes has increased substantially in recent years. Examples of the preparation and characterization of cyclotrisilanes, both symmetrically' and unsymmetrically2 substituted, have appeared. More recently, the preparation and characterization of a spiro-[2.2]pentasilane has been r e p~r t e d ,~ and the first example of the tetrasilabicyclo [ 1.1 .O] butane system, 1,3-di-tert-butyl-2,2,4,4tetrakis(2,6-diethylphenyl)tetrasilabicyclo[ 1.1 .O] butane (1) has H \ Ar AT \ / 10" H 3 1 I Ar = 2 6-diethylphenyli 2 1984, 777-778.

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Section: Resultsmentioning

confidence: 99%

The structure and barrier to inversion of tetrasilabicyclo[1.1.0]butane. Comparison to bicyclo[1.1.0]butane

Collins¹,

Dutler²,

Rauk³

1987

J. Am. Chem. Soc.

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“…In addition, TABs are isoelectronic to triphenylmethane cations and can therefore provide further information about this important class of dyes. Although the electrochemistry [14][15][16] and photophysics [17][18][19] of simple TABs, such as triphenylborane or trimesitylborane, have been the subject of various publications in the past decades, some aspects of the properties of their donor-substituted analogues still demand further investigation. Especially, the symmetry of the ground state, which has been studied intensively for triphenylborane and related model compounds [18,[20][21][22][23] and for triphenylmethane dyes, [24,25] is still a controversial topic.…”

Section: Introductionmentioning

confidence: 99%

Electrochemistry and Photophysics of Donor‐Substituted Triarylboranes: Symmetry Breaking in Ground and Excited State

Stahl

Lambert

Kaiser

et al. 2006

Chemistry A European J

161

152

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We synthesized a series of amino substituted triarylboranes (TABs) 1-3 by copper(I)-catalyzed cross-coupling reactions. The title compounds were investigated by means of cyclic voltammetry (CV) and UV-visible absorption and fluorescence spectroscopy. Electrochemical oxidation of tris(4-carbazolyl-2,6-dimethylphenyl)borane (3) leads to the formation of an electroactive polymer film on the electrode surface. The charge-transfer (CT) absorption band of all three TABs shows a pronounced negative solvatochromism, while the emission is positively solvatochromic. By combining Jortner's theory, AM1 computations, and electrooptical absorption measurements (EOAM), this unexpected behavior was shown to be due to a dipole inversion upon S0-->S1 excitation. Furthermore, polarized steady-state fluorescence spectroscopy and EOAM prove that the ground-state geometry of 3 is of lower symmetry than D3 and that the excitation energy can be transferred from one subchromophore to another within the lifetime of the excited state. Exciton-coupling theory was used to quantitatively analyze this excitation transfer.

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“…In the UV/Vis spectra, compounds 3a – e , 4a , and 4b exhibited absorption maxima at 345–365 nm in chloroform, which were assigned to the π–π* transition (Table , Figures S1 and S2). The π–π* absorption maxima were redshifted and the molar absorption coefficients were higher compared with those of trimesitylborane ( λ max = 331 nm, ε = 1.6 × 10 4 cm –1 m –1 in methylcyclohexane or isooctane) and tris(4‐bromo‐2,6‐dimethylphenyl)borane ( λ max = 334 nm, ε = 1.8 × 10 4 cm –1 m –1 in chloroform), which have smaller π‐conjugated systems. The changes in the absorption maxima wavelengths and molar absorption coefficients between trimesitylborane and compound 3a were comparable to those between tris(2,3,5,6‐tetramethylphenyl)borane ( λ max = 327 nm, ε = 1.4 × 10 4 cm –1 m –1 in THF) and tris(2,3,5,6‐tetramethyl‐1,1′;4′,1′′‐terphenyl‐4‐yl)borane ( λ max = 333 nm, ε = 2.9 × 10 4 cm –1 m –1 in THF), showing that the triazole ring was as well‐conjugated as a benzene ring.…”

Section: Resultsmentioning

confidence: 99%

An Azide‐Substituted Triarylborane: A Key Compound for the Facile Synthesis of Fluorescent Triarylboranes Bearing Triazole Moieties as Connectable π‐Conjugated System Linkages

et al. 2019

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Tris(4‐azido‐2,6‐dimethylphenyl)borane was readily synthesized from an amino‐substituted triarylborane using tert‐butyl nitrite and trimethylsilylazide. This compound can easily be converted into triarylboranes bearing various π‐conjugated moieties with triazole ring π‐linkers through a Huisgen cycloaddition. UV/Vis absorption spectra and DFT calculations suggested that constructing a triazole linker successfully extended the π‐conjugated system of triarylboranes. Triarylboranes obtained using this method maintained their fluorescent nature. In particular, the triarylborane linking N,N‐dimethylaminophenyl groups with triazole rings exhibited notable visible solvatofluorochromism and fluorescence color change upon addition of a fluoride anion.

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Charge-Transfer States in Boranes and Carbonium Ions. Their Ultraviolet Spectra

Cited by 42 publications

References 1 publication

The structure and barrier to inversion of tetrasilabicyclo[1.1.0]butane. Comparison to bicyclo[1.1.0]butane

The structure and barrier to inversion of tetrasilabicyclo[1.1.0]butane. Comparison to bicyclo[1.1.0]butane

Electrochemistry and Photophysics of Donor‐Substituted Triarylboranes: Symmetry Breaking in Ground and Excited State

An Azide‐Substituted Triarylborane: A Key Compound for the Facile Synthesis of Fluorescent Triarylboranes Bearing Triazole Moieties as Connectable π‐Conjugated System Linkages

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