Intramolecular charge-transfer fluorescence of 1-phenyltridecamethylbicyclo[2.2.2]octasilane

Molecular Silicon Clusters

The continuously decreasing size of device features in microelectronics draws growing attention to the structuring of silicon at the molecular level with powerful tools provided by synthetic chemistry. Silicon clusters are of particular importance in this regard not only as potential precursors for silicon deposition but also as well-defined model systems for bulk and surfaces of silicon at the nanoscale as well as possible starting points for future construction of molecularly precise device structures. This review aims to give a comprehensive overview about the state of the art in the synthesis of molecular silicon clusters, which are grouped into (1) electron-precise saturated clusters, (2) soluble polyhedral Zintl anions, and (3) unsaturated silicon clusters, the so-called siliconoids. Particular attention is paid to functionalization as it is generally considered a necessary prerequisite for the design and construction of more extended systems. The interrelations between the three different classes of molecular silicon clusters, e.g., arising from the introduction of negatively charged functional groups, are highlighted on grounds of NMR properties and computed electronic structures.

Simultaneous synthesis and characterization of in/out-isomers of disilabicyclo[14.14.14]alkanes

Facile and simultaneous synthesis of diphenyl-disilabicyclo[14.14.14]alkane in/out-isomers was achieved by using organosilicon chemistry. Although the formation of several in/out-isomers would be conceivable, only two diastereomers, i.e. the (traditional-)out,out-isomer and the twist-out,out-isomer, could be isolated because of homeomorphic isomerization. Crystal structures of the diastereomers were confirmed.

Steric effects on the intramolecular charge transfer fluorescence of benzo[b]thiophene-1,1-dioxide bridged macrocages

Intramolecular charge transfer (ICT) fluorescence has been widely investigated and exploited in sensor molecules. However, steric effects on the ICT fluorescence properties have rarely been reported so far, although research in this area would promote an understanding of the basics of solvation. Herein, we report the detailed fluorescence properties of bis(trimethylsilyl)benzo[b]thiophene-1,1-dioxide (TMSBTO2) and its caged cyclophanes and non-cage isomers, which demonstrate ICT fluorescence in various solutions. The fluorescence band maxima for these benzo[b]thiophene-1,1-dioxides (BTO2s) showed a red-shift with increasing solvent polarity, confirming ICT fluorescence characteristics. The linearity of the Lippert-Mataga plots was confirmed for all ICT fluorescence measured in hexane, toluene, AcOEt, CH2Cl2, and EtOH. The slopes of the plots decreased in the following order: TMSBTO2, non-cage isomers, and caged BTO2s. It is concluded that the Onsager radii for these BTO2s were increased in the abovementioned order, assuming that the difference in the dipole moments between the excited and ground states for these BTO2s was identical.

Structurally and conformationally defined small methyl polysilanes

Possessing the property of sigma-bond electron delocalisation, polysilanes are a class of compounds with unique properties. In recent years major progress has been achieved in the theoretical understanding and the synthesis of polysilanes. Much insight into the connection between conformation and electronic properties has been gained from studies of defined small polysilane molecules. The transition from Wurtz type coupling reactions to the stepwise construction of polysilane molecules employing silyl anions as key intermediates has permitted access to defined compounds with a higher degree of structural complexity. Besides this, several methods have been developed to control the conformational properties and thus gain control over the electronic properties of polysilanes.