Live-cell Raman imaging based on bioorthogonal Raman probes with distinct signals in the cellular Raman-silent region (1800–2800 cm−1) has attracted great interest in recent years. We report here a class of water-soluble and biocompatible polydiacetylenes with intrinsic ultrastrong alkyne Raman signals that locate in this region for organelle-targeting live-cell Raman imaging. Using a host-guest topochemical polymerization strategy, we have synthesized a water-soluble and functionalizable master polydiacetylene, namely poly(deca-4,6-diynedioic acid) (PDDA), which possesses significantly enhanced (up to ~104 fold) alkyne vibration compared to conventional alkyne Raman probes. In addition, PDDA can be used as a general platform for multi-functional ultrastrong Raman probes. We achieve high quality live-cell stimulated Raman scattering imaging on the basis of modified PDDA. The polydiacetylene-based Raman probes represent ultrastrong intrinsic Raman imaging agents in the Raman-silent region (without any Raman enhancer), and the flexible functionalization of this material holds great promise for its potential diverse applications.
The conductivity (dark and photo) and the short-circuit photocurrent in symmetrical thin-layer cells containing zinc octakisw-decoxyethy1)porphyrin (ZnODEP) were determined as functions of temperature with the ZnODEP in the solid, liquid crystal, and isotropic liquid states. ZnODEP, a discotic liquid crystal, organizes to form columns, which act as one-dimensional conductors, in the solid and liquid crystal phases. The changes in conductivity and photocurrent are interpreted by changes in structure and disordering (melting) that affect the rate of charge transport and trapping in the ZnODEP layer.
Millimeter-sized organic single-crystal slices of methylpyrroporphyrin XXI ethyl ester (MPPEE) have been prepared by capillary filling at its melting point (∼250°C) between two parallel pieces of glass coated with indium-tin oxide (ITO) and separated by about 2-3 µm. Crystal orientation was characterized with polarized light under an optical microscope. MPPEE single-crystal slices with different orientations appeared as dramatically different colors between two crossed polarizers. The relationship between crystal orientation and optoelectronic properties was investigated by monitoring the photocurrent flow through ITO/MPPEE/ ITO symmetrical sandwich cells. The short-circuit photocurrent strongly depended on crystal orientation, varying by more than 1 order of magnitude. When a light spot (∼150 µm in diameter) was scanned across adjacent MPPEE single-crystal domains with different orientations, short-circuit photocurrents generated at different spots within the same crystal domain were essentially constant, but they changed substantially among different domains. The photocurrent changed abruptly at domain boundaries.
Numerous mechanisms have been proposed for polymerization to provide qualitative and quantitative prediction of how monomers spatially and temporally arrange into the polymeric chains. However, less is known about this process at the molecular level because the ultrafast chemical reaction is inaccessible for any form of microscope so far. Here, to address this unmet challenge, a stimulated Raman scattering microscope based on collinear multiple beams (COMB‐SRS) is demonstrated, which allows label‐free molecular imaging of polymer synthesis in action at speed of 2000 frames per second. The field of view of the developed 2 kHz SRS microscope is 30 × 28 µm2 with 50 × 46 pixels and 7 µs dwell time. By catching up the speed of chemical reaction, COMB‐SRS is able to quantitatively visualize the ultrafast dynamics of molecular vibrations with submicron spatial resolution and sub‐millisecond temporal resolution. The propagating polymer waves driven by reaction rate and persistent UV initiation are observed in situ. This methodology is expected to permit the development of novel functional polymers, controllable photoresists, 3D printing, and other new polymerization technologies.
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