||Ryoichi Ishimatsu, Hirosato Shintaku, Yuto Kage, Misaki Kamioka, Soji Shimizu, Koji Nakano, Hiroyuki Furuta, Toshihiko Imato, Efficient Electrogenerated Chemiluminescence of Pyrrolopyrrole Aza-BODIPYs in the Near-Infrared Region with Tripropylamine
Involving Formation of S2 and T2 States, Journal of the American Chemical Society, 10.1021/jacs.9b05245, 141, 30, 11791-11795, 2019.07, Efficient electrogenerated chemiluminescences (ECLs) of three pyrrolopyrrole aza-BODIPYs in the near-infrared region by using tripropylamine as a coreactant are reported. Kinetic analysis based on Marcus theory indicates the direct formation of S2 and T2 states through the electron transfer reaction, which affects the ECL efficiencies..
||Ryoichi Ishimatsu, Shigeyuki Matsunami, Takashi Kasahara, Jun Mizuno, Tomohiko Edura, Chihaya Adachi, Koji Nakano, Toshihiko Imato, Electrogenerated chemiluminescence of donor-acceptor molecules with thermally activated delayed fluorescence, Angewandte Chemie - International Edition, 10.1002/anie.201402615, 53, 27, 6993-6996, 2014.07, The electrochemistry and electrogenerated chemiluminescence (ECL) of four kinds of electron donor-acceptor molecules exhibiting thermally activated delayed fluorescence (TADF) is presented. TADF molecules can harvest light energy from the lowest triplet state by spin up-conversion to the lowest singlet state because of small energy gap between these states. Intense green to red ECL is emitted from the TADF molecules by applying a square-wave voltage. Remarkably, it is shown that the efficiency of ECL from one of the TADF molecule could reach about 50 %, which is comparable to its photoluminescence quantum yield. Donor-acceptor molecules with thermally activated delayed fluorescence (TADF) at room temperature can emit efficient electrogenerated chemiluminescence (ECL). Efficient spin up-conversion from triplet to singlet excited states through thermal activation is required to break through the theoretical limitation according to spin statistics (25 % of the quantum yield of photoluminescence). The ECL efficiency one TADF molecule reached about 50 %..
||Ryoichi Ishimatsu, Shigeyuki Matsunami, Katsuyuki Shizu, Chihaya Adachi, Koji Nakano, Toshihiko Imato, Solvent effect on thermally activated delayed fluorescence by 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene, Journal of Physical Chemistry A, 10.1021/jp404120s, 117, 27, 5607-5612, 2013.07, Thermally activated delayed fluorescence (TADF) is fluorescence arising from a reverse intersystem crossing (RISC) from the lowest triplet (T 1) to the singlet excited state (S1), where these states are separated by a small energy gap (ΔEst), followed by a radiative transition to the ground state (S0). Rate constants relating TADF processes in 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN) were determined at four different solvent polarities (toluene, dichloromethane, ethanol, and acetonitrile). We revealed that the rate constant of RISC, kRISC, which is the most important factor for TADF, was significantly enhanced by a reduced ΔEst in more polar solvents. The smaller ΔEst was mainly attributable to a stabilization of the S1 state. This stabilization also induced a Stokes shift in fluorescence through a relatively large change of the dipole moment between S1 and S0 states (17 D). Despite of this factor, we observed a negative correlation between ΔEst and efficiency of the delayed fluorescence (pd). This was ascribed to a lower intersystem crossing rate, kISC, and increased nonradiative decay from S1, knrs, in polar solvents..
||Mei Shen, Ryoichi Ishimatsu, Jiyeon Kim, Shigeru Amemiya, Quantitative imaging of ion transport through single nanopores by high-resolution scanning electrochemical microscopy, Journal of the American Chemical Society, 10.1021/ja3023785, 134, 24, 9856-9859, 2012.06, Here we report on the unprecedentedly high resolution imaging of ion transport through single nanopores by scanning electrochemical microscopy (SECM). The quantitative SECM image of single nanopores allows for the determination of their structural properties, including their density, shape, and size, which are essential for understanding the permeability of the entire nanoporous membrane. Nanoscale spatial resolution was achieved by scanning a 17 nm radius pipet tip at a distance as low as 1.3 nm from a highly porous nanocrystalline silicon membrane in order to obtain the peak current response controlled by the nanopore-mediated diffusional transport of tetrabutylammonium ions to the nanopipet-supported liquid-liquid interface. A 280 nm × 500 nm image resolved 13 nanopores, which corresponds to a high density of 93 nanopores/μm 2. A finite element simulation of the SECM image was performed to assess quantitatively the spatial resolution limited by the tip diameter in resolving two adjacent pores and to determine the actual size of a nanopore, which was approximated as an elliptical cylinder with a depth of 30 nm and major and minor axes of 53 and 41 nm, respectively. These structural parameters were consistent with those determined by transmission electron microscopy, thereby confirming the reliability of quantitative SECM imaging at the nanoscale level..
||Ryoichi Ishimatsu, Anahita Izadyar, Benjamin Kabagambe, Yushin Kim, Jiyeon Kim, Shigeru Amemiya, Electrochemical mechanism of ion-ionophore recognition at plasticized polymer membrane/water interfaces, Journal of the American Chemical Society, 10.1021/ja207297q, 133, 40, 16300-16308, 2011.10, Here, we report on the first electrochemical study that reveals the kinetics and molecular level mechanism of heterogeneous ion-ionophore recognition at plasticized polymer membrane/water interfaces. The new kinetic data provide greater understanding of this important ion-transfer (IT) process, which determines various dynamic characteristics of the current technologies that enable highly selective ion sensing and separation. The theoretical assessment of the reliable voltammetric data confirms that the dynamics of the ionophore-facilitated IT follows the one-step electrochemical (E) mechanism controlled by ion-ionophore complexation at the very interface in contrast to the thermodynamically equivalent two-step electrochemical-chemical (EC) mechanism based on the simple transfer of an aqueous ion followed by its complexation in the bulk membrane. Specifically, cyclic voltammograms of Ag +, K+, Ca2+, Ba2+, and Pb 2+ transfers facilitated by highly selective ionophores are measured and analyzed numerically using the E mechanism to obtain standard IT rate constants in the range of 10-2 to 10-3 cm/s at both plasticized poly(vinyl chloride) membrane/water and 1,2-dichloroethane/water interfaces. We demonstrate that these strongly facilitated IT processes are too fast to be ascribed to the EC mechanism. Moreover, the little effect of the viscosity of nonaqueous media on the IT kinetics excludes the EC mechanism, where the kinetics of simple IT is viscosity-dependent. Finally, we employ molecular level models for the E mechanism to propose three-dimensional ion-ionophore complexation at the two-dimensional interface as the unique kinetic requirement for the thermodynamically facilitated IT..
||Ryoichi Ishimatsu, Jiyeon Kim, Ping Jing, Christopher C. Striemer, David Z. Fang, Philippe M. Fauchet, James L. McGrath, Shigeru Amemiya, Ion-selective permeability of an ultrathin nanoporous silicon membrane as probed by scanning electrochemical microscopy using micropipet-supported ITIES tips, Analytical Chemistry, 10.1021/ac1005052, 82, 17, 7127-7134, 2010.09, We report on the application of scanning electrochemical microscopy (SECM) to the measurement of the ion-selective permeability of porous nanocrystalline silicon membrane as a new type of nanoporous material with potential applications in analytical, biomedical, and biotechnology device development. The reliable measurement of high permeability in the molecularly thin nanoporous membrane to various ions is important for greater understanding of its structure-permeability relationship and also for its successful applications. In this work, this challenging measurement is enabled by introducing two novel features into amperometric SECM tips based on the micropipet-sup-ported interface between two immiscible electrolyte solutions (ITIES) to reveal the important ion-transport properties of the ultrathin nanopore membrane. The tip of a conventional heat-pulled micropipet is milled using the focused ion beam (FIB) technique to be smoother, better aligned, and subsequently, approach closer to the membrane surface, which allows for more precise and accurate permeability measurement. The high membrane permeability to small monovalent ions is determined using FIB-milled micropipet tips to establish a theoretical formula for the membrane permeability that is controlled by free ion diffusion across water-filled nanopores. Moreover, the ITIES tips are rendered selective for larger polyions with biomedical importance, i.e., polyanionic pentasaccharide Arixtra and polycationic peptide protamine, to yield the membrane permeability that is lower than the corresponding diffusion-limited permeability. The hindered transport of the respective polyions is unequivocally ascribed to electrostatic and steric repulsions from the wall of the nanopores, i.e., the charge and size effects..
||Ryoichi Ishimatsu, Fumiko Shigematsu, Takuma Hakuto, Naoya Nishi, Takashi Kakiuchi, Structure of the electrical double layer on the aqueous solution side of the polarized interface between water and a room-temperature ionic liquid, tetrahexylammonium bis(trifluoromethylsulfonyl)imide, Langmuir, 10.1021/la0623073, 23, 2, 925-929, 2007.01, The structure of the electrical double layer on the aqueous solution side has been studied by measuring electrocapillary curves at the polarized interface between a room-temperature ionic liquid (RTIL), tetrahexylammonium bis(trifluoromethylsulfonyl)imide, and water (W) at different concentrations of LiCl. Thermodynamic analysis of the electrocapillary curves indicates that Li+ ions negatively adsorb at the point of zero charge. The adsorption of Li+ and Cl- ions in the polarized potential window of about 200 mV can be explained by the Gouy's double layer model, and the specific adsorption of Li+ and Cl- ions at the RTIL|W interface is negligible within the polarized potential window..