Lo Pik Kwan, Li King Fai, Wong Man Shing, Cheah Kok Wai
Department of Chemistry, Hong Kong Baptist University, Kowloon Tong, Hong Kong SAR, China.
J Org Chem. 2007 Aug 31;72(18):6672-9. doi: 10.1021/jo070607z. Epub 2007 Aug 4.
A novel series of monodisperse, multi-dipolar zigzag oligoaryleneethynylenes DA(n) and D-Ar-A(n), bearing electron-donating dibenzothiophene and electron-accepting dibenzothiophene dioxide as arenes, with up to six charge-transfer (dipolar) units have been designed and synthesized by palladium-catalyzed Sonogashira coupling reactions. The linear and nonlinear optical properties of these multi-dipolar oligoaryleneethynylenes can easily be modified or enhanced by incorporating/extending with various central aryleneethynyl moieties such as phenylethynyl, oligo(9,9-dibutylfluorenyl)ethynyl, and oligothienylethynyl within the donor-acceptor units. Interestingly, the absorption and emission of these zigzag oligoaryleneethynylenes are not dependent on the number of covalently linked dipolar chromophores; however, the fluorescence quantum efficiencies consistently decrease with increased number of covalently linked dipolar units. These zigzag oligoaryleneethynylenes exhibit a linear increase in the two-photon absorption (TPA) cross-sections with increased number of covalently linked dipolar units without red-shifting the absorption and emission spectra. In addition, very large TPA cross-sections in the femtosecond regime (sigma(800) = 1306 GM in DMF or sigma(750) = 1522 GM in CH(2)Cl(2)) were obtained for D-TF-A(4) despite the moderate strength of the donor-acceptor pair. Our results suggest that the TPA properties of these zigzag oligoaryleneethynylenes including TPA wavelength and TPA cross-section can easily be tuned by means of modifying the central aryleneethynylene units and increasing the number of dipolar units, respectively. This approach provides an alternative means to tune or enhance the TPA cross-section at a specific wavelength.
通过钯催化的Sonogashira偶联反应，设计并合成了一系列新型的单分散、多偶极锯齿形低聚亚芳基乙炔DA(n)和D-Ar-A(n)，它们以给电子的二苯并噻吩和吸电子的二苯并噻吩二氧化物作为芳烃，含有多达六个电荷转移（偶极）单元。通过在供体-受体单元中引入/扩展各种中心亚芳基乙炔部分，如苯乙炔基、低聚（9,9-二丁基芴基）乙炔基和低聚噻吩乙炔基，可以轻松地改变或增强这些多偶极低聚亚芳基乙炔的线性和非线性光学性质。有趣的是，这些锯齿形低聚亚芳基乙炔的吸收和发射并不依赖于共价连接的偶极发色团的数量；然而，荧光量子效率随着共价连接的偶极单元数量的增加而持续降低。这些锯齿形低聚亚芳基乙炔的双光子吸收（TPA）截面随着共价连接的偶极单元数量的增加呈线性增加，而吸收和发射光谱没有红移。此外，尽管供体-受体对的强度适中，但对于D-TF-A(4)，在飞秒范围内获得了非常大的TPA截面（在DMF中σ(800)=1306 GM，或在CH₂Cl₂中σ(750)=1522 GM）。我们的结果表明，通过分别修饰中心亚芳基乙炔单元和增加偶极单元的数量，可以轻松调节这些锯齿形低聚亚芳基乙炔的TPA性质，包括TPA波长和TPA截面。这种方法提供了一种在特定波长下调节或增强TPA截面的替代手段。
