Charge-Compensated N-Doped π-Conjugated Polymers: Toward both Thermodynamic Stability of N-Doped States in Water and High Electron Conductivity.

The understanding and applications of electron-conducting π-conjugated polymers with naphtalene diimide (NDI) blocks show remarkable progress in recent years. Such polymers demonstrate a facilitated n-doping due to the strong electron deficiency of the main polymer chain and the presence of the positively charged side groups stabilizing a negative charge of the n-doped backbone. Here, the n-type conducting NDI polymer with enhanced stability of its n-doped states for prospective "in-water" applications is developed. A combined experimental-theoretical approach is used to identify critical features and parameters that control the doping and electron transport process. The facilitated polymer reduction ability and the thermodynamic stability in water are confirmed by electrochemical measurements and doping studies. This material also demonstrates a high conductivity of 10-2  S cm-1  under ambient conditions and 10-1  S cm-1  in vacuum. The modeling explains the stabilizing effects  for various dopants. The simulations show a significant doping-induced "collapse" of the positively charged side chains on the core bearing a partial negative charge. This explains a decrease in the lamellar spacing observed in experiments. This study fundamentally enables a novel pathway for achieving both thermodynamic stability of the n-doped states in water and the high electron conductivity of polymers.

Flexible Pressure Sensors Based on the Controlled Buckling of Doped Semiconducting Polymer Nanopillars.

Mechanically flexible and electrically conductive nanostructures are highly desired for flexible piezoresistive pressure sensors toward health monitoring or robotic skin applications. The popular approach for these sensors is to combine flexible but insulating polymers as a micro- or nanostructural functional medium and conductive materials covering the polymer surface, which could give rise to many practical issues, for example, durability, compatibility, and complicated processing steps. We herein report a piezoresistive pressure sensor with a functional component of nanopillars of a doped semiconducting polymer, operating at low bias voltage with a sensing mechanism based on controlled buckling. Nanopillars of poly(3-hexylthiophene-2,5-diyl) doped with 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane are patterned using anodic aluminum oxide templates. The nanopillars impart reversible current changes in response to the applied pressure over a wide pressure range (0-400 kPa). The sensor exhibits two current response regimes. Below 50 kPa, a strongly nonlinear response is observed, and above 50 kPa, a linear pressure response is demonstrated. Euler buckling theory is used to predict the deformation behavior of the nanopillars under pressure and in turn elucidate the sensing mechanism. Our results demonstrate that the contact area between the nanopillars and the top electrode increases with the application of pressure due to their elastic buckling in a two-regime fashion underlining the two electrical current response regimes of the sensor. Independent finite element modeling and scanning electron microscopy measurements corroborated this sensing mechanism. In contrast to many reported pressure sensors, the controlled elastic buckling of the nanopillars enables the detection of pressure over a wide range with good sensitivity, excellent reproducibility, and cycling stability.

Computationally image-corrected dual-comb microscopy with a free-running single-cavity dual-comb fiber laser.

Dual-comb microscopy (DCM), an interesting imaging modality based on the optical-frequency-comb (OFC) mode and image pixel one-to-one correspondence, benefits from scan-less full-field imaging and simultaneous confocal amplitude and phase imaging. However, the two fully frequency-stabilized OFC sources requirement hampers DCM practicality due to the complexity and costs. Here, a bidirectional single-cavity dual-comb fiber laser (SCDCFL) is adopted as a DCM low-complexity OFC source. Although the residual timing jitter in the SCDCFL blurs the image of a static object acquired by DCM, computational image correction significantly suppresses the image blur. Nanometer-order step surface profilometry with a 14.0 nm uncertainty highlights the computationally image-corrected DCM effectiveness. We further discuss a possibility to expand the computational image correction to a dynamic object and demonstrate its preliminary experiment. The proposed method enhances the DCM generality and practicality due to low-complexity OFC source.

Optical image amplification in dual-comb microscopy.

Dual-comb microscopy (DCM), based on a combination of dual-comb spectroscopy (DCS) with two-dimensional spectral encoding (2D-SE), is a promising method for scan-less confocal laser microscopy giving an amplitude and phase image contrast with the confocality. However, signal loss in a 2D-SE optical system hampers increase in image acquisition rate due to decreased signal-to-noise ratio. In this article, we demonstrated optical image amplification in DCM with an erbium-doped fiber amplifier (EDFA). Combined use of the image-encoded DCS interferogram and the EDFA benefits from not only the batch amplification of amplitude and phase images but also significant rejection of amplified spontaneous emission (ASE) background. Effectiveness of the optical-image-amplified DCM is highlighted in the single-shot quantitative nanometer-order surface topography and the real-time movie of polystyrene beads dynamics under water convection. The proposed method will be a powerful tool for real-time observation of surface topography and fast dynamic phenomena.

Horizontal Transmission of Symbiotic Green Algae Between Hydra Strains.

Some hydra strains belonging to the vulgaris group show a symbiotic relationship with green algae Chlorococcum sp. The symbiotic green algae can escape from the host polyps and can form swimming zoospores (which have two flagella) in culture solution. We observed that co-culture with the symbiotic polyps caused horizontal transmission of the symbionts into some non-symbiotic hydra strains that have no symbionts in nature and that belong not only to the vulgaris group but also to other hydra species groups. Although most of the horizontal transmission has ended in transient symbioses, a newly formed symbiosis between the symbiotic Chlorococcum sp. and strain 105 of Hydra vulgaris (Hydra magnipapillata) has been sustained for more than five years and has caused morphological and behavioral changes in the host polyps. We named this strain 105G. The asexual proliferation rate by budding increased under light conditions, although the feeding activity decreased and the polyp size was reduced in strain 105G. This new symbiosis between Chlorococcum sp. and strain 105G of H. vulgaris provides us with an intriguing research system for investigating the origin of symbiosis.

Probing DNA mismatched and bulged structures by using 19F NMR spectroscopy and oligodeoxynucleotides with an 19F-labeled nucleobase.

In this study, DNA local structures with bulged bases and mismatched base pairs as well as ordinary full-matched base pairs by using (19)F NMR spectroscopy with (19)F-labeled oligodeoxynucleotides (ODNs) were monitored. The chemical shift change in the (19) F NMR spectra allowed discrimination of the DNA structures. Two types of ODNs possessing the bis(trifluoromethyl)benzene unit (F-unit) at specified uridines were prepared and hybridized with their complementary or noncomplementary strands to form matched, mismatched, or bulged duplexes. By using ODN F1, in which an F-unit was connected directly to a propargyl amine-substituted uridine, three local structures, that is, full-matched, G-U mismatch, and A-bulge could be analyzed, whereas other structures could not be discriminated. A molecular modeling study revealed that the F-unit in ODN F1 interacted little with the nucleobases and sugar backbone of the opposite strand because the linker length between the F-unit and the uridine base was too short. Therefore, the capacity of ODN F1 to discriminate the DNA local structures was limited. Thus, ODN F2 was designed to improve this system; aminobenzoic acid was inserted between the F-unit and uridine base so the F-unit could interact more closely with the opposite strand. Eventually, the G-bulge and T-U mismatch and the three aforementioned local structures could be discriminated by using ODN F2. In addition, the dissociation processes of these duplexes could be monitored concurrently by (19)F NMR spectroscopy.