Helicenes Built from Silacyclopentadienes via Ring‐by‐Ring Knitting of the Helical Framework

Despite the apparent diversity of the protocols developed for the synthesis of helicenes, they essentially follow the same strategy: the closure of one, or several, internal rings in a key step. Herein, we report the synthesis of a new family of the heterohelicenes consisting of fused silacyclopentadiene rings formed via a facile and novel process. The treatment of oligo(alkynilydenesilylene) precursors of type H₂C=CH?(SiMe₂?C≡C)_n?R (n=3–7), bearing a vinyl group on the terminal silicon atom, with 9‐borabicyclononane leads first to 1,2‐hydroboration of the terminal double bond which then continues with a cascade of intramolecular 1,1‐carboboration reactions accompanied with the closure of a new silole ring after each step affording the target silahelicenes with, currently, up to seven condensed silole rings and with excellent yields. According XRD analysis, the seven fused silole rings of the heptacyclic compound 11 b form an almost complete turn of a helix. The presented one‐pot sequence of reactions is the first example of ring‐by‐ring knitting of a helical framework starting from easily available linear precursors.     

氟取代噻咯衍生物结构和光电性能的理论研究

采用密度泛函理论在B3LYP/6-31G(d)水平上计算了1,1-二甲基-2,3,4,5-四苯基噻咯(PSP)及其8种氟取代衍生物的几何结构与光电性质. 计算结果表明, 2,5位苯基上氟取代对PSP结构和光电性质的影响主要由氟原子的取代位置决定, 而取代基个数的增加能加强相关影响. 苯基上邻对位氟取代对分子构型影响较大, 导致HOMO-LUMO能隙增大, 光谱显著蓝移; 而间位氟取代显示诱导作用突出, 使2,5位侧链吸电子能力增强, 同时LUMO能级降低, 电子亲和势增大更有利于电子的注入.     

Synthesis of functionalized siloles from Si-tethered diynes

A new synthetic itinerary to silole from Si-tethered diynes is reported. In this protocol, the Si-tethered diyne manifests definitely the reactivity of monoyne to form the lithio silole via zirconacyclopetadiene, 1,4-diiodo-1,3-butadiene, and the corresponding dilithiodiene successively. Lithio siloles thus obtained above could be easily functionalized to give various types of silole derivatives. Complex structure like bridged bis-silole compounds could also be constructed by this process.     

Reactions of dilithiobutadienes with monochlorosilanes: Observation of facile loss of organic groups from silicon

Reactions of 1,4-dilithiobutadienes (from 1,4-diiodo-1,2,3,4-tetraethylbutadiene (1) and 2,2′-dibromobiphenyl (7) with t-BuLi) with Me₃SiCl gave siloles (3 and 9a) as the major products. No evidence for a disilylated butadiene was obtained. Use of higher molecular weight chlorosilanes ((allyl)Me₂SiCl, BnMe₂SiCl, and PhMe₂SiCl) with dibromide 7 gave dimethylsilole 9a and a silane (10a, 10b, or 10c) resulting from trapping of the organic group by the chlorosilane.     

New carbazole-substituted siloles for the fabrication of efficient non-doped OLEDs

New aggregation-induced emission molecules of carbazole-substituted siloles are prepared, based on which efficient non-doped OLEDs are fabricated, offering high external quantum efficiencies of up to 5.63%.     

Disilane- and siloxane-bridged biphenyl and bithiophene derivatives as electron-transporting materials in OLEDs

Optical, electrochemical, and electron-transporting properties of disilane- and siloxane-bridged biphenyl and bithiophene derivatives were investigated, in comparison with those of the monosilane-bridged analogues (siloles). The UV spectra and cyclic voltammograms indicated that elongation of the silicon bridge suppresses the π-conjugation, in accordance with the results of DFT calculations. The DFT calculations indicated also that the disilane-bridged biphenyl and siloxane-bridged bithiophene should have the low-lying HOMOs and LUMOs. The electron-transporting properties were evaluated by the performance of triple-layered OLEDs having vapor-deposited films of the Si-bridged compound, Alq₃, and TPD, as the electron-transport, emitter, and hole-transport, respectively. Of these, the device with a disilane-bridged biphenyl exhibited the high performance with the maximum current density of 590 mA/cm² at the applied electric field of 12 × 10⁷ V/m (applied bias voltage = 13 V) and the maximum luminance of 22 000 cd/m² at 13 × 10⁷ V/m.     

Preparation of 1,1-disubstituted silacyclopentadienes

Several new 1,1-disubstituted siloles containing substituents on the ring carbon atoms have been synthesized. The new siloles: 1,1-dihydrido-2,5-bis(trimethylsilyl)-3,4-diphenylsilole (5), 1,1-dihydrido-2,5-dimethyl-3,4-diphenylsilole (6), 1,1-dimethoxy-2,5-bis(trimethylsilyl)-3,4-diphenylsilole (7), 1,1-bis(4-methoxyphenyl)-2,5-bis(trimethylsilyl)-3,4-diphenylsilole (8), 1,1-dipropoxy-2,5-bis(trimethylsilyl)-3,4-diphenylsilole (9), and 1,1-dibromo-2,5-bis(trimethylsilyl)-3,4-diphenylsilole (13) were prepared from reactions originating from the previously reported, 1,1-bis(diethylamino)-2,5-bis(trimethylsilyl)-3,4-diphenylsilole (1) or 1,1-bis(diethylamino)-2,5-dimethyl-3,4-diphenylsilole (2). In addition, three other new organosilane byproducts were observed and isolated during the current study, bis(4-methoxyphenyl)bis(phenylethynyl)silane (11), bis(4-methoxyphenyl)di(propoxy)silane (12) and 1-bromo-4-bromodi(methoxy)silyl-1,4-bis(trimethylsilyl)-3,4-diphenyl-1,3-butadiene (14). Compounds 13 and 14 were characterized by X-ray crystallography and 14 is the first 1,1-dibromosilole whose solid state structure has been determined.     

4,4,5,5-Tetra(3,5-dibromophenyl)-2,2-diphenyl-1,3-dioxa-2-silole and related compounds as precursors to flame retardant oligomers

Certain strained five-membered heterocycles undergo thermally-induced, carbon-carbon bond homolysis to generate diradicals capable of initiating vinyl polymerization. These compounds usually contain two oxygen atoms and a larger heteroatom (silicon, phosphorus, sulfur) in addition to carbon. If the heterocycle is suitably substituted with halogen (particularly bromine) containing moities it may function as a vehicle to permit incorporation of flame-retarding units into a polymer or oligomer. When an appropriate heterocycle is used as an initiator for radical polymerization each polymer chain formed contains at least one flame-retarding unit. One such heterocycle is 4,4,5,5-tetra(3,5-dibromophenyl)-2,2-diphenyl-1,3-dioxa-2-silole. In instances in which the heterocycle also acts as a monomer, i.e., it is reactive toward chain-propagating radicals, additional flame-retarding activity may be incorporated into the polymer.