Electrochromism in an Organopolysilane

Intuitive Understanding of σ Delocalization in Loose and σ Localization in Tight Helical Conformations of an Oligosilane Chain

“…For n = 16, we also optimized the all-cisoid conformation (c; w % 378). From earlier work, [12,13,15,20] the g, o,and t conformations at internal SiSi bonds are known to represent local minima on the potentiale nergy surfaces of short permethylated oligosilanes, and chains substituted with longera lkyls occasionally show additional minima at c and d conformations. The optimization of the e, d,a nd a conformations, which do not correspond to minimai nt he potential energy surface of permethylated oligosilanes, was constrained in that the dihedral angles were set equal to the values specified above.…”

“…[1][2][3][4] They are sensitive to the backbone conformation and as ar esult lead to phenomena such as thermochromism, [5][6][7][8][9] piezochromism, [10,11] electrochromism, [12] ionochromism, [13,14] and solvatochromism. [15] Also their single-molecule electrical conductivity appearst od epend on conformation.…”

Organotin Polymers

“…Many of these materials show better sigma conductivity than the corresponding polysilanes and have been used as light-emitting diodes. 240 Much of the interest in the polysilanes, polygermanes, and polystannanes involves their s-delocalization and their σ-π delocalization when coupled with arenes or acetylenes. This is not unexpected since silicon exists as a covalent network similar to diamond.…”

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

“…[14][15][16][17] Perhaps the most striking of these is near-UV absorption, remarkable in view of the absence of any classical chromophores, such as multiple bonds, lone pairs, or aromatic rings. The sensitivity of s delocalization to the silicon backbone conformation is believed to be responsible for polysilane thermochromism, [18][19][20][21][22] piezochromism, [23,24] electrochromism, [25] ionochromism, [26,27] and solvatochromism. [28] Perhaps the most convincing piece of direct evidence for the effect of s-bond delocalization on the properties of saturated silicon chains is the long known, [29][30][31] strong red shift of the lowest energy intense UV absorption band of permethylated oligosilanes Si n Me 2n + 2 upon chain-length extension, which presumably reflects the properties of the dominant all-transoid conformer, at least in the low-temperature limit.…”