Wearable pressure sensors have demonstrated great potential in detecting pulse pressure waves on the skin for the noninvasive and continuous diagnosis of cardiac conditions. However, difficulties lie in positioning conventional single-point sensors on an invisible arterial line, thereby preventing the detection of adequate signal amplitude for accurate pulse wave analysis. Herein, we introduce the spatiotemporal measurements of arterial pulse waves using wearable active-matrix pressure sensors to obtain optimal pulse waveforms. We fabricate thin-film transistor (TFT) arrays with high yield and uniformity using inkjet printing where array sizes can be customizable and integrate them with highly sensitive piezoresistive sheets. We maximize the pressure sensitivity (16.8 kPa −1 ) and achieve low power consumption (10 1 nW) simultaneously by strategically modulating the TFT operation voltage. The sensor array creates a spatiotemporal pulse wave map on the wrist. The map presents the positional dependence of pulse amplitudes, which allows the positioning of the arterial line to accurately extract the augmentation index, a parameter for assessing arterial stiffness. The device overcomes the positional inaccuracy of conventional single-point sensors, and therefore, it can be used for medical applications such as arterial catheter injection or the diagnosis of cardiovascular disease in daily life.
The macroscopic device performance of organic solar cells is governed by interface physics on a nanometer scale. A comb-like bilayer all-polymer morphology featuring a controlled enhancement in donor-acceptor interfacial area is employed as a model system to investigate the fundamental processes of exciton separation and polaron recombination in these devices. The different nanostructures are characterized locally by SEM/AFM, and the buried interdigitating interface of the final device architecture is statistically verified on a large area via advanced grazing incidence X-ray scattering techniques. The results show equally enhanced harvesting of photoexcitons in both donor and acceptor materials directly correlated to the total enhancement of interfacial area. Apart from this beneficial effect, the enhanced interface leads to significantly increased polaron recombination losses both around the open-circuit voltage and maximum power point, which is determined in complement with diode dark current characteristics, impedance spectroscopy, and transient photovoltage measurements. From these findings, it is inferred that a spatially optimized comb-like donor-acceptor nanonetwork alone is not the ideal morphology even though often postulated. Instead, the energetic landscape has to be considered. A perfect morphology for an excitonic solar cell must be spatially and energetically optimized with respect to the donor-acceptor interface.
We investigated unsubstituted poly(para-phenylene) (PPP), a long-desired prototype of a conjugated polymer semiconductor. PPP was accessed via thermal aromatization of a precursor polymer bearing kinked, solubility-inducing dimethoxycyclohexadienylene moieties. IR spectroscopy and Vis ellipsometry studies revealed that the rate of conversion of the precursor to PPP increases with temperature and decreases with film density, indicating a process with high activation volume. The obtained PPP films were analyzed in thin-film transistors to gain insights into the interplay between the degree of conversion and the resulting p-type semiconducting properties. The semiconducting behavior of PPP was further unambiguously proven through IR and transistor measurements of molybdenum trioxide p-doped films.
The synthesis of unsubstituted, structurally perfect poly(para-phenylene) (PPP) has remained elusive for many decades. By modifying our previously reported precursor route towards PPP, we were able to simplify and optimize the precursor polymer synthesis and yields, the thermal conversion process to PPP, and the resulting material properties. We describe the synthesis of unprecedented anti-dialkoxycyclohexadienylenes, polymerized via Suzuki coupling to yield linear PPP precursor polymers. Changing the geometry and overall shape of the precursor viz upon going from syn-to anti-configuration of the monomer has two important consequences: (i) formation of the precursor polymer becomes more selective since cyclization of the monomer is no longer possible and (ii) the precursor polymer adopts a "stretched" geometry and becomes more similar to the rigid-rod of PPP, impacting the aromatization process and material properties. Films of the precursor polymers are thermally aromatized via dealkoxylation to yield structurally perfect and highly ordered, insoluble PPP. Long-range ordering within the thin films, not observed for its syn-analog, is induced as evidenced by atomic force microscopy, X-ray scattering, and IR and UV−vis/photoluminescence spectroscopy. The aromatization temperature, now feasible for fabrication of plastic devices, is significantly lowered from previously reported 300 °C to below 250 °C. The kinetics of the aromatization process were monitored via time-dependent IR measurements at different annealing temperatures, showing much faster quantitative aromatization for thin layers.
π-conjugated gels are potentially useful for organic electronic applications. We present a π-conjugated ion gel, composed of substituted poly(para-phenyleneethynylene) (PPE) and an ionic liquid. This combination is well suited as an active material in a light-emitting electrochemical cells (LECs). The nanosegregated structure of the gels achieves a large interface between the polymer and ionic liquid (IL) and allowsby nature of its structurefacile ion conduction and continuous electrical conduction paths. Efficient doping significantly improves the response time. This concept should be applicable to other π-conjugated gels, and it allows the construction of gel-LECs.
For cost-efficient organic electronic devices, the consecutive deposition of active layers by solution-based processes is a key benefit. We report a synthetic approach enabling solubility reduction of bis(cyclopentadienyl)-substituted polyfluorenes as emissive layers in organic light-emitting diodes (OLEDs). Thermally induced retro-Diels–Alder reaction liberates free cyclopentadiene as “protecting group” and pending cyclopentadienyl units, which cross-link the polymer strands upon cooling via [4+2] cycloadditions. The activation temperature is tuned in the range of 180–250 °C through alkyl, alkoxy, or ester linkages. Ultimately, macrocyclic self-protected bis(cyclopentadienylene) moieties avoid extrusion of volatile cyclopentadiene during activation. The solvent resistance of the emissive layers after cross-linking is examined by absorption spectroscopy and white light scanning interferometry. The influence of the desolubilization procedure on the performance of solution-processed OLEDs is investigated.
The fabrication of electronic, photonic, and metamaterial-based devices, or tissue engineering requires the controlled deposition and patterning of materials. Electron-beam lithography (EBL) offers unprecedented miniaturization of those devices because of its high resolution. We present a concept to induce a classic photochemical reaction in condensed matter via EBL. We investigate the response of a tetrameric cinnamate monomer in thin films toward photon and electron radiation. In the solid state, photoexcitation and electron bombardment similarly induce [2 + 2] cycloadditions, forming insoluble truxilic acid esters, as shown via IR spectroscopy measurements. Subsequently, we employed the investigated material as an electron-beam resist, showing resistance against wet-chemical etchants. Structures with resolution down to 60 nm were obtained, not achievable with conventional photolithography, proving that [2 + 2] cycloaddition of cinnamic acid containing compounds is suitable for applications in the field of EBL.
The synthesis of unsubstitutedo ligo-para-phenylenes (OPP)e xceeding para-hexaphenylene-in the literature often referredt oasp-sexiphenyl-has long remained elusive due to their insolubility.W er eport the first preparationo f unsubstituted para-nonaphenylenes (9PPs) by extending our precursor route to poly-para-phenylenes(PPP)t oadiscrete oligomer.T wo geometric isomerso fm ethoxylated syn-a nd anti-cyclohexadienylenes were synthesized,f rom which 9PP was obtained via thermal aromatization in thin films. 9PP was characterized via optical,i nfrared and solid-state 13 CNMR spectroscopy as well as atomicf orce microscopy and mass spectrometry,a nd compared to polymeric analogues. Due to the lack of substitution, para-nonaphenylene, irrespectiveo ft he precursor isomer employed, displays pronounced aggregationi nt he solid state. Intermoleculare xcitonic coupling leads to formation of H-typea ggregates, redshiftinge mission of the films to greenish. 9PP allows to study the structure-property relationship of para-phenylene oligomers and polymers, especiallys ince the opticalp roperties of PPP depend on the molecular shapeo ft he precursor.
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