Photo-detrapping of solvated electrons in an ionic liquid

金沢大学理工研究域自然システム学系We studied the dynamics of photo-detrapped solvated electrons in the ionic liquid trimethyl-N-propylammonium bis(trifluoromethanesulfonyl)imide (TMPA-TFSI) using laser flash photolysis. The solvated electrons were produced by the electron photodetachment from iodide via a 248 nm KrF excimer laser. The solvated electron decayed by first-order kinetics with a lifetime of about 240 ns. The spectrum of the solvated electron in the ionic liquid TMPA-TFSI is very broad with a peak around 1100 nm. After the 248 nm pulse, a 532 nm pulse was used to subsequently detrap the solvated electrons. After the detrapping pulse, quasi-permanent bleaching was observed. The relative magnitude of the bleaching in the solvated electron absorbance was measured from 500 to 1000 nm. The amount of bleaching depends on the probe wavelength. The fraction of bleached absorbance was larger at 500 nm than that at 1000 nm, suggesting that there are at least two species that absorb 532 nm light. We discuss the present results from viewpoint of the heterogeneity of ionic liquids. © 2009 Elsevier Ltd

定常蛍光及び時間分解蛍光分光法を用いた分子内プロトン移動反応への溶媒和不均一性効果の研究

京都大学0048新制・課程博士博士(理学)甲第17850号理博第3904号新制||理||1563(附属図書館)30670京都大学大学院理学研究科化学専攻(主査)教授 寺嶋 正秀, 教授 竹腰 清乃理, 准教授 熊﨑 茂一学位規則第4条第1項該当Doctor of ScienceKyoto UniversityDGA

Excitation wavelength dependence of photo-induced intramolecular proton transfer reaction of 4′-N,N-diethylamino-3-hydroxyflavone in various liquids

Excitation wavelength dependence of photo-induced intramolecular excited state proton transfer reaction of 4′-N, N-diethylamino-3-hydroxyflavone in various liquids has been investigated by steady-state and time-resolved fluorescence measurements. It was found that the relative fluorescence intensity of the tautomer excited state to that of the normal excited state significantly decreases in ionic liquids with changing the excitation wavelength from 380 to 470 nm. The initial proton transfer rate excited at 470 nm was different from that obtained at 400 nm excitation. The excitation wavelength dependence was discussed in relation with the inhomogeneous distribution of the solute in the ionic liquids

Feature selection in molecular graph neural networks based on quantum chemical approaches

Feature selection is an important topic that has been widely studied in data science. Recently, graph neural networks (GNNs) and graph convolutional networks (GCNs) have also been employed in chemistry. To enhance the performance characteristics of the GNN and GCN in the field of chemistry, the feature selection should also be discussed in detail from the chemistry viewpoint. Thus, this study proposes a new feature in molecular GNNs based on the quantum chemical approaches and discusses the accuracy, overcorrelation between features, and interpretability. From the overcorrelation and accuracy, the important graph convolution (IGC) with molecular-atomic properties (MAP) proposed herein showed good performance. Moreover, the integrated gradients analysis showed that the machine learning model with the IGC(MAP) explained the prediction outputs reasonably

Interpretable attribution assignment for octanol-water partition coefficient

With the increasing development of machine learning models, their credibility has become an important issue. In chemistry, attribution assignment is gaining relevance in designing molecules and debugging models. However, attention has been paid to which atoms are important in the prediction without considering whether the attribution is reasonable. In this study, we developed a graph neural network model, a high interpretable attribution model in chemistry, and modified the integrated gradients method. The credibility of our approach was confirmed by predicting the octanol--water partition coefficient (logP) and evaluating the three metrics --accuracy, consistency, and stability-- in the attribution assignment

Feature attributions for water-solubility predictions obtained by artificial intelligence methods and chemists

Recently, the field of explainable artificial intelligence has attracted significant research interest, with a particular focus on “feature attribution” in the field of chemistry. However, studies comparing the relationship between artificial-intelligence- and human-based feature attributions when predicting the same outcome are scarce. Hence, the current study aims to investigate this relationship by comparing machine-learning-based feature attributions (graph neural networks and integrated gradients) with those of chemists (Hansch–Fujita method) when predicting water solubility. The findings reveal that the artificial-intelligence-based attributions are similar to those of chemists despite their distinct origins

Excitation Wavelength Dependence of Excited State Intramolecular Proton Transfer Reaction of 4′‑<i>N</i>,<i>N</i>‑Diethylamino-3-hydroxyflavone in Room Temperature Ionic Liquids Studied by Optical Kerr Gate Fluorescence Measurement

Excited state intramolecular proton transfer reactions (ESIPT) of 4′-<i>N</i>,<i>N</i>-diethylamino-3-hydroxyflavone (DEAHF) in ionic liquids have been studied by steady-state and time-resolved fluorescence measurements at different excitation wavelengths. Steady-state measurements show the relative yield of the tautomeric form to the normal form of DEAHF decreases as excitation wavelength is increased from 380 to 450 nm. The decrease in yield is significant in ionic liquids that have cations with long alkyl chains. The extent of the decrease is correlated with the number of carbon atoms in the alkyl chains. Time-resolved fluorescence measurements using optical Kerr gate spectroscopy show that ESIPT rate has a strong excitation wavelength dependence. There is a large difference between the spectra at a 200 ps delay from different excitation wavelengths in each ionic liquid. The difference is pronounced in ionic liquids having a long alkyl chain. The equilibrium constant in the electronic excited state obtained at a 200 ps delay and the average reaction rate are also correlated with the alkyl chain length. Considering the results of the steady-state fluorescence and time-resolved measurements, the excitation wavelength dependence of ESIPT is explained by state selective excitation due to the difference of the solvation, and the number of alkyl chain carbon atoms is found to be a good indicator of the effect of inhomogeneity for this reaction