回転するサンプルホルダーが新しいタイプの中性子実験を可能にする Rotating sample holder enables new types of neutron experiments
2024-05-28 オークリッジ国立研究所(ORNL)
＜関連情報＞
- https://www.ornl.gov/news/sample-materials-can-now-take-tumble
- https://pubs.acs.org/doi/10.1021/acs.jpclett.3c02343
- https://pubs.aip.org/aip/rsi/article-abstract/94/8/085102/2905596/Photochemistry-sample-sticks-for-inelastic-neutron?redirectedFrom=fulltext
テトラセンにおける有利な一重項核分裂のための分子間励起状態ジオメトリーの測定 Measuring Intermolecular Excited State Geometry for Favorable Singlet Fission in Tetracene
Daniel Vong, Farahnaz Maleki, Eric C. Novak, Luke L. Daemen, and Adam J. Moulé
The Journal of Physical Chemistry Letters Published:January 25, 2024
DOI:https://doi.org/10.1021/acs.jpclett.3c02343
Abstract
Singlet fission (SF) is the process of converting an excited singlet to a pair of excited triplets. Harvesting two charges from a single photon has the potential to increase photovoltaic device efficiencies. Acenes, such as tetracene and pentacene, are model molecules for studying SF. Despite SF being an endoergic process for tetracene and exoergic for pentacene, both acenes exhibit near unity SF quantum efficiencies, raising questions about how tetracene can overcome the energy barrier. Here, we use recently developed instrumentation to measure inelastic neutron scattering (INS) while optically exciting the model molecules using two different excitation energies. The spectroscopic results reveal intermolecular structural relaxation due to the presence of a triplet excited state. The structural dynamics of the combined excited state molecule and surrounding tetracene molecules are further studied using time-dependent density functional theory (TD-DFT), which shows that the singlet and triplet levels shift due to the excited state geometry, reducing the uphill energy barrier for SF to within kT.
中性子非弾性散乱用光化学サンプルスティック Photochemistry sample sticks for inelastic neutron scattering
Daniel Vong;Eric C. Novak;Adam J. Moulé;Luke L. Daemen
Review of Scientific Instruments Published:August 04 2023
DOI:https://doi.org/10.1063/5.0154605
Every material experiences atomic and molecular motions that are generally termed vibrations in gases and liquids or phonons in solid state materials. Optical spectroscopy techniques, such as Raman, infrared absorption spectroscopy, or inelastic neutron scattering (INS), can be used to measure the vibrational/phonon spectrum of ground state materials properties. A variety of optical pump probe spectroscopies enable the measurement of excited states or elucidate photochemical reaction pathways and kinetics. So far, it has not been possible to study photoactive materials or processes in situ using INS due to the mismatch between neutron and photon penetration depths, differences between the flux density of photons and neutrons, cryogenic temperatures for INS measurements, vacuum conditions, and a lack of optical access to the sample space. These experimental hurdles have resulted in very limited photochemistry studies using INS. Here we report on the design of two different photochemistry sample sticks that overcome these experimental hurdles to enable in situ photochemical studies using INS, specifically at the VISION instrument at Oak Ridge National Laboratory. We demonstrate the use of these new measurement capabilities through (1) the in situ photodimerization of anthracene and (2) the in situ photopolymerization of a 405 nm photoresin using 405 nm excitation as simple test cases. These new measurement apparatus broaden the science enabled by INS to include photoactive materials, optically excited states, and photoinitiated reactions.
