Development of radical initiator based on o-imino-isourea capable of photo/thermal polymerization.

Using o-imino isourea, three photo- and thermal dual-responsive radical initiators dicyheDCC, CyheDCC, and BnDCC were systematically developed and synthesized. By adding an aromatic ring to the free radical initiators, the ultraviolet-visible absorption was redshifted, and the absorption coefficient was increased. Compared with other initiators, BnphDCC exhibited an exceptional photoinitiation rate under photo-differential scanning calorimetry (DSC) and a high absorption coefficient (ε = 15 420 M-1 cm-1). Therefore, it is an appropriate potential photoinitiator. DicyheDCC, which was composed of a cyclic hydrocarbon, exhibited rapid thermal initiation (Tpeak = 82 °C) during thermal DSC, making it a valuable thermal radical initiator. Because of the low stiffness of the N-O link in radical initiators, density functional theory predicts that the aliphatic ring has a significantly lower enthalpy than the aromatic ring. Moreover, in this study, CyhephDCC and BnphDCC, as dual-responsive radical initiators, indicated the potential for a photo- and heat dual-curing system through the universal free-radical polymerization of acrylates. These significant discoveries may be useful for developing efficient and diversified polymer network systems that require synergistic photo- and thermal effects.

Naphthalene diimide-based random terpolymers with axisymmetric and asymmetric electron acceptors for controllable morphology and enhanced fill factors in all-polymer solar cells.

All-polymer solar cells (all-PSCs), based on p-type polymer donors and n-type acceptors as the active layer, offer exceptional promise because of excellent thermal stability, superior film formation, and good mechanical stress as a unique bulk heterojunction (BHJ) solar cell combination. Therefore, tuning the molecular composition between polymers is crucial for optimizing power conversion efficiency (PCE) in these all-PSC systems. In this study, we synthesized a series of naphthalene diimide (NDI)-based random terpolymers P(NDI-BDD10), P(NDI-TPD10), P(NDI-TT10), and P(NDI-2FQ10) with axisymmetric (BDD, TPD) and asymmetric (TT, 2FQ) electron acceptors. Compared with the blend morphology of PBDB-T:N2200, their diverse effects due to the addition of trace amounts of axisymmetric and asymmetric components were comprehensively investigated using physical and surface analyses and structural simulations. Consequently, most of our polymer acceptors demonstrated improved fill factors (FFs) in the optimal morphology. P(NDI-BDD10)-based devices achieved the highest PCE of 6.80% and FF of 69.1%, while the architecturally most asymmetric P(NDI-TT10)-based devices reached the lowest PCE of 4.52% despite an enhanced FF of 65.4%. As a result, the appropriate molecular arrangement is crucial for obtaining the desired morphology and improved PCE. Our findings give novel molecular design insight into the distinctions between axisymmetric and asymmetric electron acceptors and seem significant for achieving improved morphological features and efficiency.

Enhanced ferroelectric switching speed of Si-doped HfO2 thin film tailored by oxygen deficiency.

Investigations concerning oxygen deficiency will increase our understanding of those factors that govern the overall material properties. Various studies have examined the relationship between oxygen deficiency and the phase transformation from a nonpolar phase to a polar phase in HfO2 thin films. However, there are few reports on the effects of oxygen deficiencies on the switching dynamics of the ferroelectric phase itself. Herein, we report the oxygen- deficiency induced enhancement of ferroelectric switching properties of Si-doped HfO2 thin films. By controlling the annealing conditions, we controlled the oxygen deficiency concentration in the ferroelectric orthorhombic HfO2 phase. Rapid high-temperature (800 °C) annealing of the HfO2 film accelerated the characteristic switching speed compared to low-temperature (600 °C) annealing. Scanning transmission electron microscopy and electron energy-loss spectroscopy (EELS) revealed that thermal annealing increased oxygen deficiencies, and first-principles calculations demonstrated a reduction of the energy barrier of the polarization flip with increased oxygen deficiency. A Monte Carlo simulation for the variation in the energy barrier of the polarization flipping confirmed the increase of characteristic switching speed.

Dual Monitoring of Cracking and Healing in Self-healing Coatings Using Microcapsules Loaded with Two Fluorescent Dyes.

We report the development of an extrinsic, self-healing coating system that shows no fluorescence from intact coating, yellowish fluorescence in cracked regions, and greenish fluorescence in healed regions, thus allowing separate monitoring of cracking and healing of coatings. This fluorescence-monitoring self-healing system consisted of a top coating and an epoxy matrix resin containing mixed dye loaded in a single microcapsule. The dye-loaded microcapsules consisted of a poly(urea-formaldehyde) shell encapsulating a healing agent containing methacryloxypropyl-terminated polydimethylsiloxane (MAT-PDMS), styrene, a photo-initiator, and a mixture of two dyes: one that fluoresced only in the solid state (DCM) and a second that fluoresced dramatically in the solid than in the solution state (4-TPAE). A mixture of the healing agent, photo-initiator, and the two dyes was yellow due to fluorescence from DCM. On UV curing of this mixture, however, the color changed from yellow to green, and the fluorescence intensity increased due to fluorescence from 4-TPAE in the solid state. When a self-healing coating embedded with microcapsules containing the DCM/4-TPAE dye mixture was scratched, the damaged region exhibited a yellowish color that changed to green after healing. Thus, the self-healing system reported here allows separate monitoring of cracking and healing based on changes in fluorescence color.

An Ultrahigh Mobility in Isomorphic Fluorobenzo[c][1,2,5]thiadiazole-Based Polymers.

To understand the effects rendered on the relevant basic physical properties and device function by controlling the regiochemistry of the cyclopenta[1,2-b:5,4-b']dithiophene-fluorobenzo[c][1,2,5]thiadiazole polymer (hereafter referred to as the CDT-FBT polymer), two polymers, the regiorandom polymer (RA) and regioregular version (RR), respectively, are synthesized and characterized. In addition, an efficient route for synthesizing a key monomer for RR using various synthesis scope and optimizing the reaction conditions is discussed. Although RA exhibits optical, electrochemical, and morphological properties similar to RR, it shows better field-effect transistor (FET) performance. Surprisingly, by employing a capillarity-mediated sandwich-casting process on a nanogrooved substrate, an unprecedented mobility of 17.8 cm2 V-1 s-1 is obtained for RA-based FETs; this mobility value is almost twofold greater than those of the corresponding RR-based FETs. For the first time, this study challenges previously reported results in that high carrier mobility is related to the high degree of polymer order induced by the backbone regioregularity.

A roundabout approach to control morphological orientation and solar-cell performance by modulating side-chain branching position in benzodithiophene-based polymers.

To be meaningful to guide the rational design of novel high-performance conjugated semiconductors, we prepared three benzo[1,2-b:4,5-b']dithiophene (BDT)-based polymers by systematically moving the branching point of the alkyl chain. The effect of side-chain engineering was thoroughly investigated by a range of techniques. We demonstrate that a subtle change in the branching position in the BDT core can have a critical impact on polymer packing and preferential backbone orientation in thin films; copolymers made from BDT and thieno[3,4-c]pyrrole-4,6-dione units (TPD) adopt more of a face-on orientation as the branching point is shifted closer to the backbone, which can be correlated with a dramatic difference in solar-cells performance. The high short-circuit current density (11.6 mA cm(-2) ) for the copolymer with one carbon atom between the alkoxylated oxygen atom and the branching point results from its predominantly face-on orientation and smoother surface in thin films, which results in power conversion efficiencies as high as 4.56 %.

Benzodipyrrolidone (BDP)-based polymer semiconductors containing a series of chalcogen atoms: comprehensive investigation of the effect of heteroaromatic blocks on intrinsic semiconducting properties.

In order to determine the effects of actual 'chalcogen atoms' on semiconducting properties for application in a variety of optoelectronic devices, a class of donor (D)-acceptor (A) polymer semiconductors, namely PBDP-Fu, PBDP-Th, and PBDP-Se, containing the recently formulated benzodipyrrolidone (BDP) accepting unit and furan (Fu), thiophene (Th), or selenophene (Se) as a donating unit has been synthesized, characterized, and used in an active layer of organic field-effect transistors (OFETs). With the LUMO levels being comparatively consistent for all three polymers (-3.58 to -3.60 eV) due to the dominant BDP contribution to the polymer backbone, the HOMO energies are somewhat sensitive to the structurally distinctive feature of the donor counits used. Utilizing a combination of X-ray diffraction (XRD) and atomic force microscopy (AFM), it is apparent that further crystalline domains occur with edge-on orientation for the polymers (PBDP-Th and PBDP-Se) with relatively heavier chalcogen atoms such as Th and Se, compared with PBDP-Fu which has a rather amorphous nature. Investigation of their OFET performance indicates that all the polymers show well balanced ambipolar operations. The desirable morphological structures of both the PBDP-Th and PBDP-Se result in higher mobilities in OFETs than those of PBDP-Fu. In particular, 200 °C annealed PBDP-Se OFETs results in ambipolarity being mobile for both holes of up to 1.7 × 10(-2) cm(2)/V·s and electrodes of up to 1.9 × 10(-2) cm(2)/V·s. In addition, OFETs with PBDP-Th show nearly equivalent charge carrier mobilities for both holes (µ(h) = 1.2 × 10(-2) cm(2)/V·s) and electrons (µ(e) = 1.1 × 10(-2) cm(2)/V·s). Consequently, we systematically demonstrate how the manipulation of existing heteroaromatics can modulate the electronic properties of conjugated D-A polymers, elucidating structure-property relationships that are desirable for the rational design of next generation materials.