Synthesis, Structure, Aggregation‐Induced Emission, Self‐Assembly, and Electron Mobility of 2,5‐Bis(triphenylsilylethynyl)‐3,4‐diphenylsiloles

Abstract

2,5-Bis(triphenylsilylethynyl)-3,4-diphenylsiloles with different 1,1-substituents [XYSi(CPh)(2) (C-C≡C-SiPh(3))(2)] (Ph=phenyl) were synthesized in high yields by the Sonogashira coupling of 2,5-dibromo-3,4-diphenylsiloles with triphenylsilylacetylene, and two of these were characterized crystallographically. Crystal structures and theoretical calculations showed that the new silole molecules had higher conjugation than 2,5-diarylsiloles. They possessed low HOMO and LUMO energy levels due to the electron-withdrawing effect of the triphenylsilylethynyl groups. Cyclic voltammetry analysis revealed low electron affinities, which were comparable to those of perfluoroarylsiloles. B3LYP/6-31* calculations demonstrated that the new siloles possessed large reorganization energies for electron and hole transfers and high electron mobilities. A mobility of up to 1.2×10(-5) cm(2) V(-1) s(-1) was obtained by the transient electroluminescence method, which was about fivefold higher than that of tris(8-hydroxyquinolinato)aluminum, a widely used electron-transport material, under the same conditions. All of the silole molecules possessed high thermal stability. Although, their solutions were weakly emissive, their nanoparticle suspensions and thin films emitted intense blue-green light upon photoexcitation, demonstrating a novel feature of aggregation-induced emission (AIE). Polarized emissions were observed in the silole crystals. The addition of solvents, which did not dissolve the silole molecules, into silole-containing solutions caused self-assembly of the molecules, which produced macroscopic fibrils with strong light emissions.

Aggregation-induced emission of siloles

“…27 While their emission efficiencies in the solution state are comparable to those of siloles with trialkylylsilyl groups, their solid-state emission efficiencies are lower (18.1–34.6%) than those of siloles with branched trialkylsilyl groups, such as the triisopropylsilyl ones (57.1–99.9%). This is because although the large-sized triphenylsilyl groups can prevent close stacking of the central silole ring, their phenyl rings could alternatively lead to π–π stacking in the aggregated state, which decreases the emission efficiency.…”

Solvatochromism, Reversible Chromism and Self‐Assembly Effects of Heteroatom‐Assisted Aggregation‐Induced Enhanced Emission (AIEE) Compounds

“…[8] The fall-known aggregation-inducede mission (AIE) or aggregation-induced enhanced emission (AIEE) phenomena reported by Tang and co-workers in 2001 effectively overcome the interference of ACQ, and have becomep opulart opics in many materials fields. [9] To date, abundant AIE/AIEE materials have been reported, [10] such as hexaphenylsilole (HPS), [11] tetraphenylethene (TPE), [12] distyrylanthracene (DSA) [13,14] and their derivatives. The AIE/AIEE materials possess amazing properties, for instance, high quantum yields, controlled self-assembly effects and photostabilities, [15][16][17] which result in potential applications in organic light-emitting diodes( OLEDs) materials, [18] label-free bioprobes, [19,20] bioimaging [21] and so on.…”

Synthesis of Siloles (and Germoles) that Exhibit the AIE Effect

“…As the bulk of the R group in the silole increased the l em was blue shifted [42]. A later study of the same series as thin films but with Ph 3 SiC À À À À À À CÀ À substituents gave lower F PL values of 18.1% (SiPh 2 ), 28.3% (SiPhMe), and 34.6% (SiMe 2 ), the reverse of the order reported in the previous study by Tang's group [43]. An earlier study with a more complex 2,5-alkynyl substituent with phenyleneethynylene strands with up to three aromatic rings and a total of three alkynes also provided quantum yields for the solid state, but the values were less that 15% (the solid-state form was not specified) [44].…”

“…A second cross-coupling route utilizes the reaction of the 2,5-ZnCl substituents with Br 2 or N-bromosuccinimide (NBS) to give a 2,5-dibromosilole, which may or may not be isolated [36]. Isolation of three dibromides with different sets of substituents at the 1,1-position (Me 2 , MePh, Ph 2 ) [37] was recently reported and earlier, isolation of three dibromides of Ph 2 Br 2 C 4 SiR 2 where R ¼ Et, i Pr, Hex was described [34a]. A very detailed account of the preparation of 2,5-dibromo-1,1-dimethyl-3,4-diphenyl-1H-silole was published in Organic Synthesis [38].…”

“…A very detailed account of the preparation of 2,5-dibromo-1,1-dimethyl-3,4-diphenyl-1H-silole was published in Organic Synthesis [38]. The 2,5-dibromosilole is useful for cross-coupling reactions (particularly with terminal alkynes [37,39]). Reaction conditions for the lithiation of one of the two bromides to give the intermediate monolithio intermediate (Ph 2 BrLiC 4 SiEt 2 ) was reported by Tamao et al [34a].…”