Intrinsic optical transitions of lower Davydov excitons in thiophene/phenylene co-oligomer ͑TPCO͒ crystals were investigated. Lower Davydov excitons are either optically allowed or forbidden depending on the number of thiophene rings constituting the TPCOs. The TPCO molecules are orientated nearly parallel to each other like H aggregates and are aligned in herringbone fashion within a crystalline layer. The transition selection rules are dominated by the components of the molecular transition dipole moments lying in the herringbone planes of the respective crystals. The selection rules at the exciton band bottoms of the TPCOs differ from those of oligothiophenes in spite of these two compounds having similar molecular structures. The selection rules vary drastically with the molecular alignment because of the H aggregation. TPCO and oligothiophene crystals are treated as H aggregates as a first approximation. This treatment is very useful for understanding the optical transitions of conjugated materials.
SUMMARYRecently, a new type of infinite elements which uses r-' decay was proposed. They were applied to exterior wave problems and good results were obtained. In two-dimensional problems, however, it was necessary to move the origin of the r -l decay in order to model the outgoing wave more accurately, because it decays roughly as r-'/'. In this paper, the mapped infinite elements with r-ll' decay and the necessary numerical integration procedure are presented. These elements d o not require any artificial movement of the origin.Several example problems are solved. The results show that the infinite elements with r -''* decay here give much more accurate values than the infinite elements with exponential decay and any damper elements.
Intracellular pH is one of the key factors for understanding various biological processes in biological cells. Plasmonic gold and silver nanoparticles (NPs) have been extensively studied for surface-enhanced Raman scattering (SERS) applications for pH sensing as a local pH probe in a living cell. However, the SERS performance of NPs depends on material, size, and shape, which can be controlled by chemical synthesis. Here, we synthesized 18 types of gold and silver NPs with different morphologies such as sphere, rod, flower, star, core/shell, hollow, octahedra, core/satellites, and chainlike aggregates, and quantitatively compared their SERS performance for pH sensing. The SERS intensity from the most commonly utilized SERS probe molecule (para-mercaptobenzoic acid, p-MBA) for pH sensing was measured at the single nanoparticle level under the same measurement parameters such as low laser power (0.5 mW/μm2), short integration time (100 ms) at wavelengths of 405, 488, 532, 584, 676, and 785 nm. In our measurement, the Ag chain, Ag core/satellites, Ag@Au core/satellites, and Au core/satellites nanoassemblies showed efficient pH sensing at the single particle level. By using p-MBA-conjugated Au@Ag core/satellites, we performed time-lapse pH measurements during apoptosis of HeLa cells. These experimental results confirmed that the pH measurement using p-MBA-conjugated Au@Ag core/satellites can be applied for long-term measurements of intracellular pH during cellular events.
Photoluminescence ͑PL͒ and optical gain measurements have been performed for single crystals of thiophene/phenylene co-oligomer at room and low temperatures. Broad PL bands are transformed to be an ensemble of several spectrally narrower vibronic peaks with decreasing temperature. Very sharp lines as narrow as ϳ3 meV are observed at 10 K under weak excitation. Intensities of sharp emission lines superlinearly increased at 10 K under intense excitation, showing the amplified spontaneous emission ͑ASE͒. The ASE bands were clearly identified to the sidebands of B 1 and A 1 + B 1 vibronic modes. The ASE is also observed at room temperature under the intense excitation. Spectroscopic investigation at varied temperatures enabled us to identify the origin of the ASE band to the vibronic sidebands of the electronic transition of the thiophene/phenylene co-oligomer crystals. In addition, highly polarized optical gains ϳ50 cm −1 were obtained for the two ASE bands at room temperature.
Visualizing live-cell uptake of small-molecule drugs is paramount for drug development and pharmaceutical sciences. Bioorthogonal imaging with click chemistry has made significant contributions to the field, visualizing small molecules in cells. Furthermore, recent developments in Raman microscopy, including stimulated Raman scattering (SRS) microscopy, have realized direct visualization of alkyne-tagged small-molecule drugs in live cells. However, Raman and SRS microscopy still suffer from limited detection sensitivity with low concentration molecules for observing temporal dynamics of drug uptake. Here, we demonstrate the combination of alkyne-tag and surface-enhanced Raman scattering (SERS) microscopy for the real-time monitoring of drug uptake in live cells. Gold nanoparticles are introduced into lysosomes of live cells by endocytosis and work as SERS probes. Raman signals of alkynes can be boosted by enhanced electric fields generated by plasmon resonance of gold nanoparticles when alkyne-tagged small molecules are colocalized with the nanoparticles. With time-lapse 3D SERS imaging, this technique allows us to investigate drug uptake by live cells with different chemical and physical conditions. We also perform quantitative evaluation of the uptake speed at the single-cell level using digital SERS counting under different quantities of drug molecules and temperature conditions. Our results illustrate that alkyne-tag SERS microscopy has a potential to be an alternative bioorthogonal imaging technique to investigate temporal dynamics of small-molecule uptake of live cells for pharmaceutical research.
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