Probing ultrafast ππ*/nπ* internal conversion in organic chromophores via K-edge resonant absorption.,Nature Communications

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Probing ultrafast ππ*/nπ* internal conversion in organic chromophores via K-edge resonant absorption.
Nature Communications ( IF 14.7 ) Pub Date : 2017-06-22 , DOI: 10.1038/s41467-017-00069-7
T J A Wolf ₁ , R H Myhre _{1,

2} , J P Cryan ₁ , S Coriani _{3,

4} , R J Squibb ₅ , A Battistoni ₁ , N Berrah ₆ , C Bostedt _{7,

8,

9} , P Bucksbaum _{1,

10} , G Coslovich ₇ , R Feifel ₅ , K J Gaffney _{1,

11} , J Grilj ₁₂ , T J Martinez _{1,

13} , S Miyabe _{1,

13,

14} , S P Moeller ₇ , M Mucke ₁₅ , A Natan ₁ , R Obaid ₆ , T Osipov ₇ , O Plekan ₁₆ , S Wang ₁ , H Koch _{1,

2} , M Gühr _{1,

17}

Affiliation

Stanford PULSE Institute, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, CA, 94025, USA.
Department of Chemistry, Norwegian University of Science and Technology, NO-7491, Trondheim, Norway.
Dipartimento di Scienze Chimiche e Farmaceutiche, Università degli Studi di Trieste, Piazzale Europa 1, Trieste, IT-34127, Italy.
Department of Chemistry, Technical University of Denmark, 2800, Kongens Lyngby, Denmark.
Department of Physics, University of Gothenburg, SE-412 96, Gothenburg, Sweden.
Department of Physics, University of Connecticut, 2152 Hillside Road, Storrs, CT, 06269, USA.
Linac Coherent Light Source, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, CA, 94025, USA.
Argonne National Laboratory, 9700 Cass Avenue, Lemont, IL, 60439, USA.
Department of Physics and Astronomy, Northwestern University, 2145 Sheridan Road, Evanston, IL, 60208, USA.
Department of Physics, Stanford University, 382 Via Pueblo Mall, Stanford, CA, 94305, USA.
Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, CA, 94025, USA.
Laboratory of Ultrafast Spectroscopy, Ecole Polytechnique Federal de Lausanne, Lausanne, CH-1015, Switzerland.
Department of Chemistry, Stanford University, 333 Campus Drive, Stanford, CA, 94305, USA.
Laser Technology Laboratory, RIKEN, Wako, Saitama, 351-0198, Japan.
Department of Physics and Astronomy, Uppsala University, Box 516, SE-751 20, Uppsala, Sweden.
Elettra-Sincrotrone Trieste, Strada Statale 14-km 163,5 AREA Science Park, IT-34149, Basovizza, Trieste, Italy.
Institut für Physik und Astronomie, Universität Potsdam, Karl-Liebknecht-Straße 24/25, DE-14476, Potsdam, Germany.

Many photoinduced processes including photosynthesis and human vision happen in organic molecules and involve coupled femtosecond dynamics of nuclei and electrons. Organic molecules with heteroatoms often possess an important excited-state relaxation channel from an optically allowed ππ* to a dark nπ* state. The ππ*/nπ* internal conversion is difficult to investigate, as most spectroscopic methods are not exclusively sensitive to changes in the excited-state electronic structure. Here, we report achieving the required sensitivity by exploiting the element and site specificity of near-edge soft X-ray absorption spectroscopy. As a hole forms in the n orbital during ππ*/nπ* internal conversion, the absorption spectrum at the heteroatom K-edge exhibits an additional resonance. We demonstrate the concept using the nucleobase thymine at the oxygen K-edge, and unambiguously show that ππ*/nπ* internal conversion takes place within (60 ± 30) fs. High-level-coupled cluster calculations confirm the method's impressive electronic structure sensitivity for excited-state investigations.Many photo-induced processes such as photosynthesis occur in organic molecules, but their femtosecond excited-state dynamics are difficult to track. Here, the authors exploit the element and site selectivity of soft X-ray absorption to sensitively follow the ultrafast ππ*/nπ* electronic relaxation of hetero-organic molecules.

中文翻译：

通过 K 边缘共振吸收探测有机发色团中的超快 ππ*/nπ* 内部转换。

许多光诱导过程（包括光合作用和人类视觉）发生在有机分子中，并涉及原子核和电子的耦合飞秒动力学。具有杂原子的有机分子通常具有从光学允许的 ππ* 到暗 nπ* 态的重要激发态弛豫通道。 ππ*/nπ* 内部转换很难研究，因为大多数光谱方法并不完全对激发态电子结构的变化敏感。在这里，我们报告通过利用近边缘软 X 射线吸收光谱的元素和位点特异性来实现所需的灵敏度。当 ππ*/nπ* 内部转换过程中 n 轨道中形成空穴时，杂原子 K 边缘处的吸收光谱表现出额外的共振。我们使用氧 K 边缘处的核碱基胸腺嘧啶证明了这一概念，并明确表明 ππ*/nπ* 内部转换发生在 (60 ± 30) fs 内。高水平耦合簇计算证实了该方法在激发态研究中令人印象深刻的电子结构灵敏度。许多光诱导过程（例如光合作用）发生在有机分子中，但其飞秒激发态动力学很难跟踪。在这里，作者利用软 X 射线吸收的元素和位点选择性来灵敏地跟踪异质有机分子的超快 ππ*/nπ* 电子弛豫。

更新日期：2017-06-26

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