Hillier Bethany K, de Clercq Damon M, Bortolussi Stephen D S, Capomolla Simona S, Nielsen Michael P, Młodzikowska-Pieńko Katarzyna, Gershoni-Poranne Renana, Schmidt Timothy W, Peeks Martin D
School of Chemistry, UNSW Sydney NSW 2052 Australia
School of Photovoltaics and Renewable Energy Engineering, UNSW Sydney NSW 2052 Australia.
Chem Sci. 2025 May 20;16(25):11331-11338. doi: 10.1039/d5sc01676b. eCollection 2025 Jun 25.
The unusual [3]radialene motif at the centre of triquino[3]radialene permits exceptional electronic conjugation between the three quinone arms of the molecule, giving rise to a remarkably low-energy and intense absorption spectrum. Since triquino[3]radialene's initial synthesis in the 1970s, questions have been posed around the molecule's potential diradical(oid) character. In this work we present new synthetic approaches to triquino[3]radialene and a thorough spectroscopic and computational evaluation of its properties. Despite broad UV-visible absorption, the triquino[3]radialene is non-emissive. An investigation by transient absorption spectroscopy reveals that the initially-formed excited state of triquino[3]radialene decays to a triplet state with a lifetime of 0.82 μs. Using computational chemistry, we compare triquino[3]radialene to Yang's biradical and galvionxyl, with which it is structurally similar. DFT reveals insights into the role of aromaticity in the photoexcited triplet state, where quinoidal rings become more aromatic. MCSCF and CIPT2 calculations reproduce the experimental spectra and reveal a diradical character of = 0.05 in triquino[3]radialene.
三醌[3]并环戊二烯中心的异常[3]并环戊二烯 motif 使得分子的三个醌臂之间能够实现特殊的电子共轭，从而产生显著低能量且强烈的吸收光谱。自20世纪70年代首次合成三醌[3]并环戊二烯以来，围绕该分子潜在的双自由基（类）特性提出了诸多问题。在这项工作中，我们展示了合成三醌[3]并环戊二烯的新方法，并对其性质进行了全面的光谱和计算评估。尽管三醌[3]并环戊二烯在紫外可见光谱范围内有广泛吸收，但它不发光。通过瞬态吸收光谱研究发现，三醌[3]并环戊二烯最初形成的激发态衰变为三重态，寿命为0.82 μs。利用计算化学，我们将三醌[3]并环戊二烯与结构相似的杨双自由基和加维奥克西尔进行了比较。密度泛函理论（DFT）揭示了光激发三重态中芳香性的作用，其中醌型环的芳香性增强。多组态自洽场（MCSCF）和完全活性空间二阶微扰理论（CIPT2）计算重现了实验光谱，并揭示了三醌[3]并环戊二烯的双自由基特征值为0.05。
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