Developing Quinoidal Fluorophores with Unusually Strong Red/Near-Infrared Emission

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• 作者：Longbin Ren ; Feng Liu ; Xingxing Shen ; Cheng Zhang ; Yuanping Yi ; Xiaozhang Zhu
• 刊名：Journal of the American Chemical Society
• 出版年：2015
• 出版时间：September 9, 2015
• 年：2015
• 卷：137
• 期：35
• 页码：11294-11302
• 全文大小：495K
• ISSN：1520-5126

文摘

Despite the dominant position of aromatic fluorophores, we report herein the design and synthesis of quinoidal fluorophores based on rarely emissive quinoidal bithiophene. Quinoidal bitheno[3,4-b]thiophene, QBTT-C6, consisting of cruciform-fused (E)-1,2-bis(5-hexylthiophen-2-yl)ethene and quinoidal bithiophene, shows a fluorescence quantum yield of 8.5%, 25-fold higher than that of the parent quinoidal QBT chromophore, but its maximum emission is at similar wavelengths. QBTT-Ar鈥檚 featuring intramolecular charge transfer can further shift the maximum emission into the near-infrared region. The intramolecular charge transfer is programmably enhanced by tuning the substituents on the aryl groups from the electron-withdrawing trifluoromethyl to the electron-donating methoxy groups. Unexpectedly, a positive relationship between intramolecular charge transfer and fluorescence quantum yield is observed; as a result, QBTT-FL gives an unprecedentedly high fluorescence quantum yield of up to 53.1% for quinoidal oligothiophenes. With detailed photophysical and theoretical investigations, we demonstrate that the nonradiative intersystem crossing (S₁ 鈫?T₂) is significantly restrained in QBTT-Ar鈥檚, which can be attributed to the faster reverse intersystem crossing (T₂ 鈫?S₁) characteristic of a small activation energy. This work reveals the possibility for developing red/near-infrared fluorophores from the less explored quinoidal molecules because of their intrinsically narrow bandgaps.