Conspectus Bis-diimine Cu(I) complexes exhibit strong absorption in the visible region owing to the metal-to-ligand charge transfer (MLCT) transitions, and the triplet MLCT (3MLCT) states have long ...lifetimes. Because these characteristics are highly suitable for photosensitizers and photocatalysts, bis-diimine Cu(I) complexes have been attracting much interest. An intriguing feature of the Cu(I) complexes is the photoinduced structural change called “flattening”. Bis-diimine Cu(I) complexes usually have tetrahedron-like D 2d structures in the ground (S0) state, in which two ligands are perpendicularly attached to the Cu(I) ion. With MLCT excitation, the central Cu(I) ion is formally oxidized to Cu(II), which induces the structural change to the “flattened” square-planar-like structure that is seen for usual Cu(II) complexes. In this Account, we review our recent studies on ultrafast excited-state dynamics of bis-diimine Cu(I) complexes carried out using femtosecond time-resolved optical spectroscopy. Focusing on three prototypical bis-diimine Cu(I) complexes that have 1,10-phenanthroline ligands with different substituents at the 2,9-positions, i.e., Cu(phen)2+ (phen = 1,10-phenanthroline), Cu(dmphen)2+ (dmphen = 2,9-dimethyl-1,10-phenanthroline), and Cu(dpphen)2+ (dpphen = 2,9-diphenyl-1,10-phenanthroline), we examined their excited-state dynamics by time-resolved emission and absorption spectroscopies with 200 fs time resolution, observed the excited-state coherent nuclear motion with 30 fs time resolution and performed complementary theoretical calculations. This combined approach vividly visualizes excited-state processes in the MLCT state of bis-diimine Cu(I) complexes. It was demonstrated that flattening distortion, internal conversion, and intersystem crossing occur on the femtosecond–early picosecond time scale, and their dynamics is clearly identified separately. The flattening distortion predominantly occurs in the S1 state on the subpicosecond time-scale, and the precursor S1 state retaining the initial undistorted structure appears as a metastable state before the structural change. This observation indicates that the traditional understanding based on the Jahn–Teller effect appears irrelevant for realistically discussing the photoinduced structural change of bis-diimine Cu(I) complexes. The lifetime of the precursor S1 state significantly depends on the substituents in the three complexes, indicating that the flattering distortion requires a longer time as the substituents at 2,9-positions of the ligands become bulkier. It is suggested that the substituents are rotated to avoid steric repulsions to achieve the flattened structure at the global minimum of the S1 state, implying the necessity of discussion based on a multidimensional potential energy surface to properly consider this excited-state structural change. After the flattening distortion, the S1 states of Cu(dmphen)2+ and Cu(dpphen)2+, which have bulky substituents, relax to the T1 state by intersystem crossing on the ∼10 ps time scale, while the flattened S1 state of Cu(phen)2+ relaxes directly to the S0 state on the ∼2 ps time scale. This difference is rationalized in terms of the different magnitude of the flattening distortion and relevant changes in the potential energy surfaces. Clear understanding of the ultrafast excited-state process provides a solid basis for designing and using Cu(I) complexes, such as controlling the structural change to efficiently utilize the energy of the MLCT state in solar energy conversion.
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We report our tip-enhanced Raman scattering (TERS) study of a pentacene derivative, where the molecule is adsorbed on the Ag tip of a scanning tunneling microscope (STM) while the facing Ag(111) ...substrate is kept atomically clean. Vibrational Raman features were observed only when the tip was approached to the substrate within the tunneling distance, indicating that the signal enhancement through the localized surface plasmon resonance at the metal nanogap is operative with this “inverted TERS” configuration. It was found that the Raman signal exhibits on/off intensity blinking repeatedly on the time scale of tens of minutes, suggesting a diffusional motion of the single adsorbate on the tip surface even at the sample temperature of 81 K. In addition to frequency fluctuations observed for particular bands, the observed spectrum occasionally showed the appearance/disappearance of bands that are assignable to infrared-active modes. This observation is rationalized by considering loss of the inversion symmetry associated with hybridization of the molecular orbitals through electronic interaction with the nonflat surface of the Ag tip. On the basis of the TERS spectral data and their temporal changes, we discuss dynamic aspects of the orbital overlap and resultant electron transfer interaction, which is expected to provide a clue to understanding the general mechanism underlying the properties and reactivity of adsorbates on realistic metal surfaces.
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Uterine cervical adenocarcinoma （ADC） has been increasing in its prevalence world widely despite the decrease of squamous cell carcinoma （SCC）. It comprises nearly 20-25% of the all cervical ...malignancy in developed countries. The worse biological behavior had been reported in patients with intermediateand high risk factors after surgery, and in advanced stage over III, radiotherapy （RT） alone and concurrent chemo-radiotherapy （CCRT） with cisplatin was not always effective. As for chemotherapy （CT）, the iaduction CT has not established, as well. Further molecular targeted therapy （MTT） has been studied. The targets of oncogenic driver mutations were vascular endothelial growth factor （VEGF） in SCC, or tyrosine kinase （TK） of endothelial growth factor receptor 2 （EGFR2, Her2/neu）-Ras-MAPK-ERK pathway. Bevacizumab （Bey, anti-VEGF monoclonal antibody） is considered as one of key agent with paclitaxel and carboplatin in SCC, but not for ADC. This article focuses on up-to-date knowledge of biology and possible specific therapeutic directions to explore in the management of cervical ADC.
For the efficient electrochemical glucose oxidation on the electrode modified with redox hydrogel involving Os-tethered polymer and flavin adenine dinucleotide-dependent glucose dehydrogenase ...(FADGDH), the effect of pore size of MgO-templated carbon (MgOC) as an electrode material was studied. The MgOC was modified on glassy carbon electrode by ink-drop-casting technique. The MgOC pore size clearly affected on the current generation efficiency for glucose oxidation. As the pore size increased above 100 nm, a glucose oxidation current density of more than 100 mA cm−2 was achieved with 1000 μg cm−2 of hydrogel loading. Both high specific surface area and macrostructure of MgOC, which does not impede mass transport even if hydrogel loading is increased, are important factors in designing the porous structure of the MgOC layer via the ink-drop-casting process during electrode fabrication.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Photodynamic therapy (PDT) utilizes photoirradiation in the presence of photosensitizers to ablate cancer cells via generation of singlet oxygen (1O2), but it is important to minimize concomitant ...injury to normal tissues. One approach for achieving this is to use activatable photosensitizers that can generate 1O2 only under specific conditions. Here, we report a novel photosensitizer that is selectively activated under hypoxia, a common condition in solid tumors. We found that introducing an azo moiety into the conjugated system of a seleno-rosamine dye effectively hinders the intersystem crossing process that leads to 1O2 generation. We show that the azo group is reductively cleaved in cells under hypoxia, enabling production of 1O2 to occur. In PDT in vitro, cells under mild hypoxia, within the range typically found in solid tumors (up to about 5% O2), were selectively ablated, leaving adjacent normoxic cells intact. This simple and practical azo-based strategy should be widely applicable to design a range of activatable photosensitizers.
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Femtosecond time-resolved absorption measurements were carried out for the dark and signaling states of a BLUF (Blue Light Using FAD) protein, PixD, from the cyanobacterium Synechocystis. When the ...dark state was excited, FAD semiquinone radical (FADH•) was produced from the S1 state, and FADH• led to the signaling state. On the other hand, photoexcitation of the signaling state generated FADH• and FAD anion radical (FAD•–), and they decayed back to the original signaling state. In both cases, FADH• was formed and decayed with a proton-coupled electron transfer (PCET) via the hydrogen-bond network that involves FAD, Gln50, and Tyr8, and hence the kinetics of FADH• directly reflects the hydrogen-bond structure in the FAD-binding sites. It was found that the formation rate of FADH• was significantly different between the dark and signaling states, whereas the decay rate was the same. This indicates that the hydrogen-bond network of FAD–Gln50–Tyr8 in the dark and signaling states is initially different but it becomes indistinguishable after FADH• is formed, implying that the FAD–Gln50–Tyr8 hydrogen-bond network is rearranged during the PCET to generate FADH•. The present results best agree with the model in which the Gln tautomerizes without rotation in the signaling-state formation.
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The photoinduced structural change of a prototype metal complex, Cu(dmphen)2+ (dmphen = 2,9-dimethyl-1,10-phenanthroline), was studied by ultrafast spectroscopy with time resolution as high as 30 fs. ...Time-resolved absorption measured with direct S1 excitation clearly showed spectral changes attributable to the D 2d (perpendicular) → D 2 (flattened) structural change occurring in the metal-to-ligand charge transfer singlet excited state (1MLCT) and the subsequent S1 → T1 intersystem crossing. It was confirmed that the two processes occur with time constants of ∼0.8 ps (structural change) and ∼10 ps (intersystem crossing), and their time scales are clearly well-separated. A distinct oscillation of the transient absorption signal was observed in the femtosecond region, which arises from the coherent nuclear motion of the perpendicular S1 state that was directly generated by photoexcitation. This demonstrated that the perpendicular S1 state has a well-defined vibrational structure and can vibrate within its subpicosecond lifetime. In other words, the S1 state stays undistorted in a short period, and the coherent nuclear motion is maintained in this state. Time-dependent density functional theory (TDDFT) calculations gave consistent results, indicating a very flat feature and even a local minimum at the perpendicular structure on the S1 potential energy surface. The vibrational assignments of the S1 nuclear wavepacket motion were made on the basis of the TDDFT calculation. It was concluded that photoexcitation induces a 1 vibrations containing the Cu–ligand bond length change and a b 1 vibration attributed to the ligand-twisting motion that has the same symmetry as the flattening distortion. Ultrafast spectroscopy and complementary quantum chemical calculation provided an overall picture and new understanding of the photoinduced structural change of the prototypical metal complex.
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Real-time observation of chemical bond formation and subsequent nuclear rearrangements is an ultimate goal of chemical science. Yet, such attempts have been hampered by the technical difficulty of ...triggering bond formation at well-defined, desired timing. The trimer of dicyanoaurate complex (Au(CN)2 –3) is an ideal system for achieving this aim because the tight covalent Au–Au bonds are formed upon photoexcitation. Despite the apparent simplicity of the system, however, recent time-resolved studies failed to construct a consistent picture of its ultrafast dynamics. Here, we report femtosecond time-domain Raman tracking of ultrafast structural dynamics of the Au(CN)2 – trimer upon photoinduced Au–Au bond formation. The obtained Raman data reveal that the Au–Au breathing vibration at ∼90 cm–1 exhibits a gradual frequency upshift in a few picoseconds, demonstrating a continuous bent-to-linear structural change on the triplet-state potential energy surface upon the Au–Au bond formation. The comprehensive ultrafast spectroscopic study settles the controversy on this prototypical molecular assembly.
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Green fluorescent protein (GFP) from jellyfish Aequorea victoria, an essential bioimaging tool, luminesces via excited-state proton transfer (ESPT) in which the phenolic proton of the ...p-hydroxybenzylideneimidazolinone chromophore is transferred to Glu222 through a hydrogen-bond network. In this process, the ESPT mediated by the low-frequency motion of the chromophore has been proposed. We address this issue using femtosecond time-resolved impulsive stimulated Raman spectroscopy. After coherently exciting low-frequency modes (<300 cm–1) in the excited state of GFP, we examined the excited-state structural evolution and the ESPT dynamics within the dephasing time of the low-frequency vibration. A clear anharmonic vibrational coupling is found between one high-frequency mode of the chromophore (phenolic CH bend) and a low-frequency mode at ∼104 cm–1. However, the data show that this low-frequency motion does not substantially affect the ESPT dynamics.
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Fluorogenic probes for bioimaging have become essential tools for life science and medicine, and the key to their development is a precise understanding of the mechanisms available for fluorescence ...off/on control, such as photoinduced electron transfer (PeT) and Förster resonance energy transfer (FRET). Here we establish a new molecular design strategy to rationally develop activatable fluorescent probes, which exhibit a fluorescence off/on change in response to target biomolecules, by controlling the twisted intramolecular charge transfer (TICT) process. This approach was developed on the basis of a thorough investigation of the fluorescence quenching mechanism of N-phenyl rhodamine dyes (commercially available as the QSY series) by means of time-dependent density functional theory (TD-DFT) calculations and photophysical evaluation of their derivatives. To illustrate and validate this TICT-based design strategy, we employed it to develop practical fluorogenic probes for HaloTag and SNAP-tag. We further show that the TICT-controlled fluorescence off/on mechanism is generalizable by synthesizing a Si–rhodamine-based fluorogenic probe for HaloTag, thus providing a palette of chemical dyes that spans the visible and near-infrared range.
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