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<p>Developing metal-free triplet-triplet annihilation upconversion systems that operate under far-red excitation and produce efficient blue emission is challenging due to an inherent trade-off between a large anti-Stokes shift and a high upconversion quantum yield. Here we show that introducing electron-withdrawing groups at the meso-position of a pentamethine cyanine scaffold narrows the singlet-triplet energy gap, suppresses photoisomerization, and promotes the&#xa0;intersystem crossing. These meso-electron-withdrawing pentamethine cyanines possess higher triplet state energy levels than their meso-unsubstituted counterparts. In particular, the meso-hemicyanine-derived sensitizer exhibits characteristic low-temperature phosphorescence. When paired with perylene, it extends the excitation wavelength to 721 nm and yields blue emission at 470 nm, yielding an upconversion quantum yield of 9.6% (upper limit 50%). This study demonstrates that molecular engineering of pentamethine cyanines via meso-position electron-withdrawing substitution effectively reduces the singlet-triplet energy gap, enabling the design of organic triplet-triplet annihilation upconversion materials and advancing their utility in photonics and biophotonics.</p>

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Meso-electron-withdrawing pentamethine cyanines achieve large anti-Stokes blue-emitting triplet-triplet annihilation upconversion

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年7月7日

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  • Zihui Zhang,
  • Ming-Yu Zhang,
  • Lin-Han Jiang,
  • Ying-Ze Li,
  • Dong-Xue Guo,
  • Yu-Qian Yang,
  • Ling Huang

摘要

Developing metal-free triplet-triplet annihilation upconversion systems that operate under far-red excitation and produce efficient blue emission is challenging due to an inherent trade-off between a large anti-Stokes shift and a high upconversion quantum yield. Here we show that introducing electron-withdrawing groups at the meso-position of a pentamethine cyanine scaffold narrows the singlet-triplet energy gap, suppresses photoisomerization, and promotes the intersystem crossing. These meso-electron-withdrawing pentamethine cyanines possess higher triplet state energy levels than their meso-unsubstituted counterparts. In particular, the meso-hemicyanine-derived sensitizer exhibits characteristic low-temperature phosphorescence. When paired with perylene, it extends the excitation wavelength to 721 nm and yields blue emission at 470 nm, yielding an upconversion quantum yield of 9.6% (upper limit 50%). This study demonstrates that molecular engineering of pentamethine cyanines via meso-position electron-withdrawing substitution effectively reduces the singlet-triplet energy gap, enabling the design of organic triplet-triplet annihilation upconversion materials and advancing their utility in photonics and biophotonics.