Impact of iodine-substitution on the symmetry and room-temperature phosphorescence behavior of thienyl diketone skeleton.

IF 3.1 2区 化学 Q3 CHEMISTRY, PHYSICAL
Daiki Shikichi, Takumi Ehara, Mao Komura, Ken Onda, Kiyoshi Miyata, Yosuke Tani
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Abstract

Introducing heavy atoms, or replacing atoms with heavier ones, is a routine approach for accelerating spin-flipping photophysical processes. However, predicting its impact on phosphorescence efficiency is not straightforward. Herein, we report an unexpected consequence of bromine-to-iodine substitution in a bromothienyl diketone derivative, TIPS-BrTn, that exhibits outstanding room-temperature phosphorescence (RTP) in cyclohexane solution. Contrary to our expectation, the iodo-congener TIPS-ITn exhibited feeble photoluminescence, which we confirmed as RTP by ultrafast spectroscopy. Further experimental and theoretical studies revealed that, in the T1 state, an excited-state symmetry breaking occurred on TIPS-ITn while TIPS-BrTn preserved the centrosymmetric geometry. We identified the driving force for the symmetry breaking as an intramolecular two-center three-electron bonding interaction between iodine and carbonyl oxygen in the (n,π*) excited state. Consequently, while the direct T1-S0 spin-orbit coupling (SOC) in TIPS-BrTn is symmetry-forbidden and zero, that of TIPS-ITn is non-zero due to the loss of centrosymmetry, thereby accelerating nonradiative T1-S0 decay to diminish the RTP. Importantly, the phosphorescence rate constant is not solely dictated by the direct T1-S0 SOC; instead, it can be rationalized by the intensity borrowing from higher singlet states. Thus, our work highlights the importance of controlling molecular symmetry, which could suppress the direct T1-S0 SOC and lead to a preferential acceleration of radiative decay over nonradiative decay for achieving efficient RTP.

碘取代对噻吩基二酮骨架对称性和室温磷光行为的影响。
引入重原子,或者用更重的原子代替原子,是加速自旋翻转光物理过程的常规方法。然而,预测其对磷光效率的影响并不简单。在此,我们报道了溴-碘取代溴噻吩基二酮衍生物TIPS-BrTn在环己烷溶液中表现出突出的室温磷光(RTP)的意想不到的结果。与我们的预期相反,碘同系物TIPS-ITn表现出微弱的光致发光,我们通过超快光谱证实了这是RTP。进一步的实验和理论研究表明,在T1态下,TIPS-ITn发生了激发态对称性破缺,而TIPS-BrTn保持了中心对称的几何结构。我们确定了对称破缺的驱动力是碘和羰基氧在(n,π*)激发态下的分子内二中心三电子键相互作用。因此,虽然TIPS-BrTn中的直接T1-S0自旋轨道耦合(SOC)是对称禁止的零,但TIPS-ITn的自旋轨道耦合(SOC)由于中心对称性的丧失而非零,从而加速了T1-S0的非辐射衰变,从而降低了RTP。重要的是,磷光速率常数并不完全由直接的t1 - so0 SOC决定;相反,它可以通过从更高的单重态中借用强度来合理化。因此,我们的工作强调了控制分子对称性的重要性,这可以抑制直接t1 - so0 SOC,并导致辐射衰变优先于非辐射衰变加速,以实现有效的RTP。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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来源期刊
Journal of Chemical Physics
Journal of Chemical Physics 物理-物理:原子、分子和化学物理
CiteScore
7.40
自引率
15.90%
发文量
1615
审稿时长
2 months
期刊介绍: The Journal of Chemical Physics publishes quantitative and rigorous science of long-lasting value in methods and applications of chemical physics. The Journal also publishes brief Communications of significant new findings, Perspectives on the latest advances in the field, and Special Topic issues. The Journal focuses on innovative research in experimental and theoretical areas of chemical physics, including spectroscopy, dynamics, kinetics, statistical mechanics, and quantum mechanics. In addition, topical areas such as polymers, soft matter, materials, surfaces/interfaces, and systems of biological relevance are of increasing importance. Topical coverage includes: Theoretical Methods and Algorithms Advanced Experimental Techniques Atoms, Molecules, and Clusters Liquids, Glasses, and Crystals Surfaces, Interfaces, and Materials Polymers and Soft Matter Biological Molecules and Networks.
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