Photophysical properties of heteroaromatic ring-fused (di)benzosiloles

Abstract

Benzosiloles fused to heterocycles such as thiophene, benzothiophene, and benzofuran, and indole-and benzosilole-fused dibenzosiloles were prepared by palladium-catalyzed intramolecular coupling of the corresponding 2-(arylsilyl)aryl triflates in good to high yields. Molecular and crystal structures of 5,7-dihydro-5,5,7,7-tetrakis(1-methylethyl)bis[1]benzosilolo-[2,3-b:3', 2'-d]thiophene, 6-methyl-12,12-diisopropyl-12H-indololo[3,2-b][1]silafluorene, and 5,5,11,11-tetraisopropyl-5,11H-benzosilolo[3,2-c]silafluorene were determined by X-ray diffraction analysis. The UV absorption spectra of the (di)benzosilole derivatives in cyclohexane red-shifted when compared to 1,1-diisopropyldibenzosilole, indicating that replacing a benzene ring of dibenzosilole by the heterocycles as well as fusion of indole and benzosilole moieties onto dibenzosilole narrowed the HOMO-LUMO gaps of the -conjugation system. The thiophene-fused benzosiloles were faintly fluorescent in solution and in the solid state, whereas the dibenzosiloles exhibited luminescence with moderate and high quantum yields in cyclohexane and in microcrystals, respectively. In other words, aggregation-induced emission was observed for the dibenzosiloles. Notably,5,5,11,silafluorene in microcrystals exhibited violet fluorescence ( max = 396 nm) with a quantum yield of 0.70. Density functional theory (DFT) calculations of the prepared (di)benzosiloles were also performed. absorption, benzosilole, fluorescence, silicon, solid-state emission

Dibenzosiloles and 12H‐Indololo[3,2‐d]naphtho[1,2‐b][1]siloles: Exploration of Organic Chromophores Exhibiting Efficient Solid‐State Fluorescence

“…The photophysical properties of 15c – 15f are summarized in Table , along with those of 3‐methoxy‐ and 3‐dimethylamino‐substituted dibenzosiloles 15a and 15b [18a]. As seen in Figure , the absorption maxima redshifted significantly when D was switched from methoxy to dimethylamino (compare 15a and 15b ) and from dimethylamino to diphenylamino (compare 15c and 15d ), and the electron‐withdrawing nature of A increased (compare 15d , 15e , and 15f ).…”

“…In contrast, 3‐D‐7‐A‐substituted dibenzosiloles, which could be regarded as the silicon analogues of the D‐π‐A‐type fluorenes, remained unexplored, probably due to the lack of facile synthetic methods for such unsymmetrical dibenzosiloles. However, the development of the palladium‐catalyzed cyclization of 2‐[3‐(diorganoamino)phenylsilyl]‐4‐cyanophenyl triflates, which gave 15c and 15d in excellent yields as single regioisomers, enabled access to the D‐π‐A‐type dibenzosiloles 15c – 15f , and allowed us to explore the potential of 15 as functional materials (Figure ) [18a]. The formyl and dicyanoethenyl derivatives 15e and 15f were easily obtained by diisobutylaluminum hydride reduction of 15d and Knoevenagel condensation of 15e with CH 2 (CN) 2 .…”

“…Then, we developed a palladium‐catalyzed intramolecular coupling of 2‐(arylsilyl)aryl triflates 10 as a novel approach to silicon‐bridged biaryls 11 [17]. This novel cyclization allowed us to synthesize symmetrical and unsymmetrical dibenzosiloles, and also various heteroaromatic ring‐fused benzosiloles, in good to excellent yields, most of which were difficult to obtain through conventional methods [18]. In addition, we found that, when 2‐(2‐indolylsilyl)aryl triflates 12 were subjected to similar reaction conditions, intramolecular direct arylation proceeded with accompanying 1,2‐migration of a silylene tether, giving rise to [1]benzosilolo[3,2‐ b ][1]indoles 13 that were intensely blue emissive in the solid state [19].…”

Silicon-Bridged Biaryls: Molecular Design, New Synthesis, and Luminescence Control

“…41 During our study of the intramolecular coupling reaction, we found that 9q and 9r, originally prepared to demonstrate the reaction scope, exhibited intense violet fluorescence in the solid state, with high quantum yields of 0.51 and 0.70, respectively ( Figure 9). 42,43 The crystal packing of 9q and 9r showed that the molecules in each crystal were well separated from one another, presumably due to the steric bulkiness of isopropyl groups. No p-p stacking, which leads to severe fluorescence quenching, was observed between adjacent molecules.…”

From China to the world: Science China Chemistry celebrates the International Year of Chemistry

“…In other words, aggregationinduced emission was observed for the dibenzosiloles. Notably, 5,5,11,11-tetraisopropyl-5,11H-benzosilolo[3,2-c]silafluorene in microcrystals exhibited violet fluorescence ( max = 396 nm) with a quantum yield of 0.70" [25]. Jingzhi Sun, Ben Zhong Tang, and coworkers reported post-functionalization of disubstituted polyacetylenes via click chemistry [26].…”