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41287-B1
Synthesis of Silole-Substituted Molecules and Polymers Toward Novel Electronic and Optical Materials
Siloles, or 1-silacyclopenta-2,4-dienes, are molecules that have potential as useful luminescent materials. Siloles have a small HOMO-LUMO gap compared to other heterocyclopentadienes and thus may have properties conducive to using them as electron transports and emissive layers in organic light-emitting diodes (OLEDs). The most common substituent on the four carbons of the silacyclopentadiene ring is the phenyl group because of easy access to inexpensive starting materials and thoroughly developed synthetic methods. The focus of the current research is the synthesis and physical properties of novel siloles, especially with various substituents on or in the phenyl groups attached to the silole ring.
Siloles can be synthesized from the reaction of diphenylacetylene with lithium metal in diethyl ether and subsequent trapping with a variety of dichlorosilanes to give the product silole. Attempts to reduce bis(4-trimethylsilylphenyl)acetylene with both stoichiometric (1:1) and excess amounts of lithium metal and subsequent trapping with dimethyl sulfate did not result in the desired silole product.
We changed our approach and utilized a nickel catalyst to react bis(4-trimethylsilylphenyl)acetylene in a 2:1 stoichiometric ratio with 1,1,2,2-tetramethyldisilane to give the desired silole in 91% yield. (TOC picture) An X-ray crystal structure was obtained. (nugget)
The newly synthesized silole was also studied by solution-state UV-vis and fluorescence spectroscopy. The trimethylsilyl-substituted silole was compared to the parent silole (with no groups on the phenyl rings). The parent silole had two major absorption bands at 249 and 356 nm, whereas the trimethylsilyl-substituted silole had absorption bands at 230 and 362 nm. When excited at 360 nm, the parent silole showed a broad emission band at 477 nm and a quantum yield of FPL = 3.1x10-4. Under the same conditions, the trimethylsilyl-substituted silole displayed a significant blue-shift to 411 nm and more strikingly, an order of magnitude larger quantum yield of FPL = 5.0x10-3.
