Institute of Chemistry, The Hebrew University of Jerusalem, Edmond J. Safra Campus, Jerusalem 91904, Israel.
Org Lett. 2020 Oct 16;22(20):7809-7813. doi: 10.1021/acs.orglett.0c02666. Epub 2020 Sep 23.
The use of polyaromatic hydrocarbons to capture and release singlet oxygen is of considerable importance in materials chemistry, synthesis, and photodynamic therapy. Here we studied the ability of a series of tethered twistacenes, possessing different degrees of backbone twist, to capture and release singlet oxygen via the reversible Diels-Alder reaction. When the twistacene acts as both a sensitizer and a diene, the photo-oxidation rate depends on the extinction coefficient of the irradiation wavelength. However, when the twistacenes function solely as a diene, the rate of photo-oxidation increases with increasing twist. The rate of the reverse reaction, the singlet oxygen release, also increases with increasing twist. The calculated transition state energy decreases with increasing twist, which can explain the observed trend. The presence of the tether significantly increases the reversibility of the reaction, which can proceed in repeated forward and reverse cycles in very high yield under mild conditions, as required for molecular switches.
多环芳烃用于捕获和释放单线态氧在材料化学、合成和光动力疗法中具有重要意义。在这里，我们研究了一系列连接的扭曲并苯，它们具有不同程度的骨架扭曲，通过可逆的 Diels-Alder 反应来捕获和释放单线态氧。当扭曲并苯既作为敏化剂又作为二烯时，光氧化速率取决于辐照波长的消光系数。然而，当扭曲并苯仅作为二烯时，光氧化速率随扭曲程度的增加而增加。反向反应，即单线态氧的释放，也随扭曲程度的增加而增加。计算得到的过渡态能量随扭曲程度的增加而降低，这可以解释所观察到的趋势。连接基团的存在显著增加了反应的可逆性，这使得反应能够在温和条件下以非常高的产率在正向和反向循环中重复进行，这是分子开关所需要的。
