Cyano-substituted tetracenes (5,11-dicyano-6,12-diphenyltetracene, Tet) undergo exoergic singlet fission (SF), a spin-allowed photophysical process that generates a pair of triplet excitons from one singlet exciton. To elucidate substituent effects on SF, we have measured the SF dynamics and triplet yields of thin films, formed by Tet bearing hydrogen (H), methyl (Me), fluoro (F), and trimethylsilyl (TMS) substituents on the p-phenyl positions and on the 3 and 9 positions of the tetracene core, by time-resolved spectroscopy in the vis-NIR and IR regions. The H-, Me-, and F-Tet display strong intramolecular electronic coupling (π–π distances <4 Å), and SF gives high triplet exciton yields up to 200% (quantitative). In addition, a charge-transfer state mediates SF in F-Tet films, while H-Tet and Me-Tet show no evidence for such a state. Correlations between the SF yields and the crystal structure show that chromophore slippage along both their short and long axes allows efficient SF and that a large degree of π contact between the chromophores is not necessary for rapid and efficient SF in the solid state. As expected, the large interchromophore distance in TMS-Tet (>4 Å) reduces its SF triplet yield to about 60%.

中文翻译：

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取代基对氰基取代的二芳基四环素多晶薄膜中单重态激子裂变的影响

氰基取代的四碳烯（5,11-二氰基-6,12-二苯并四苯，Tet）经历放热单线裂变（SF），这是一种自旋允许的光物理过程，可以从一个单重态激子产生一对三重态激子。为了阐明取代基对SF的影响，我们测量了由Tet在对苯基上带有氢（H），甲基（Me），氟（F）和三甲基甲硅烷基（TMS）取代基的Tet形成的薄膜的SF动态和三重态收率。通过在vis-NIR和IR区域中进行时间分辨光谱分析，发现并四苯芯的3个位置和3个位置和9个位置。该^ h - ，我- ，和F-春节显示出强分子内电子耦合（π-π距离<4Å），而SF给出高达200％（定量）的高三重态激子产率。另外，电荷转移状态介导了F-Tet膜中的SF ，而H-Tet和Me-Tet没有显示出这种状态的证据。SF收率与晶体结构之间的相关性表明，生色团沿其短轴和长轴的滑动允许有效的SF，发色团之间的大量π接触对于固态的快速高效的SF是不必要的。如所预期的，TMS-Tet中较大的发色团距离（> 4Å ）将其SF三重态收率降低至约60％。